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					             Theoretical study of the quaternary GaInAsN based lasers
                    for the 1.3 and 1.55 m wavelength range


                               H.Mebtouche a, M.E.H.Louhibi a, H.Abid b
                                             a) ICEP Laboratory
                                      b) Applied Materials Laboratory
                        Research Center, University of Djillali-liabes of Sidi-Bel-Abbes,
                                            22000 Sidi bel abbes

         The development of a novel materials system, GaInAsN lattice-matched to GaAs, for long-wavelength
semiconductor lasers were studied. The GaInAsN quantum well and multi-quantum wells have shown promising
potential in the fabrication of long-wavelength vertical cavity surface emitting lasers, which are very important
devices for broadband optical networks. Important issues concerning the performance of GaInAsN quantum
wells, such as the annealing on threshold current density and emission wavelength will be discussed in this
paper. In order to make the optimisation for some parameters of GaInAsN material, under certain condition, can
be well described by a small number of parameters that can be extracted from small signal and used for furher
optimisation.

I Introduction                                             Furthermore, GaInAsN exhibits a large conduction
          As the personal computer becomes                 band offset, allowing for better thermal performance
pervasive in this world, so does the demand for            for VCSELs [3].
network access. Moore’s Law states that                             There are significant challenges for
microprocessors will halve in price and double in          GaInAsN before its realization in reliable, useful
computing power every eighteen months. As a                VCSELs. The threshold current density and the
consequence of computing growth and greater                lasing threshold of GaInAsN remain high. This paper
affordability for users, Gilder’s Law states that the      will report on the current methods for performance
bandwidth of voice and data communications                 enhancement in (1.3 and 1.55 m) long-wavelength
systems will triple every twelve months. The               GaInAsN quantum well and double quantum wells
recourse in response to the exponentially increasing       VCSELs, including the threshold current density of
network demand is the development of optical               two structures, and to see the difference in order to be
fiber[1] network infrastructures. Light propagation        able to make the good choice.
in optical fibers has zero dispersion and minimal
attenuation at wavelengths of 1.3 m and 1.55 m,          II Active region
respectively. Thus, long-wavelength (1.3 and 1.55                    The short optical length of the gain medium
m) vertical cavity surface emitting lasers (VCSELs)       in a VCSEL is partly compensated by the very high
are ideal light sources for fiber optic communication      reflectivity of the Bragg mirros. Despite this the
systems.                                                   active medium must still be capable of producing
          Conventional long wavelength VCSELs              considerable gain, this is why quantum wells are used
have been fabricated using the quaternary compound         as active material in VCSELs.
GaInAsP grown on an InP substrate. It is, however,                   The structure of a QW is similar to that of a
not without its disadvantages. The GaInAsP/InP             DH except that in the former case the thickness of the
system exhibits poor electron confinement and as a         active region is kept much smaller. Figure I shows
result, a low level of thermal conductivity and low        the typical structure of a GaInAsN/GaAs quantum
characteristic temperature. The refractive index of the    well.
GaInAsP/InP material system is small (~0.25).
Consequently, it is impractical to grow distributed
Bragg reflectors (DBRs), which are fundamental to
the functionality of a VCSEL, on InP using lattice-
matched GaInAsP/InP materials.
          Initially reported by a group from Hitachi
[2], GaInAsN has been shown to be a viable
alternative. GaInAsN, grown on a GaAs substrate,
has better electron confinement and higher thermal            FigureI :Structure of a GaInAsN/GaAs
conductivity than GaInAsP/InP. Since GaInAsN is               quantum well.
grown on GaAs, technically matured GaAs/AlGaAs
                                                                    Electron and holes are confined to the
DBRs can be used in the GaInAsN VCSELs. The
                                                           central well region by the band structure at the
GaAs/AlGaAs bi-layer has a larger index difference
                                                           interface. If the length of region is made small
(~0.7) than the GaInAsP/InP combination. This
                                                           enough (determined by de Broglie equation), the
allows for easier fabrication of DBRs for GaInAsN.
confinement of the carriers in one direction will
result in energy sub-bands.
          The relation between the energy of the first                                                       Dconf(A°)                       100         200      300           400    500    600
sub-band and the QW width is given by the following                                                            (La=80A°)                    0.019 0.028 0.034 0.037 0.038 0.037
expression:
                                                                                                                                            0.036 0.043 0.046 0.047 0.046 0.044
                                           2 2
                                 E  Eg                                 (Eq-1)                              (La=100A°)
                                          2mr l 2                                                                                           0.081 0.091 0.094 0.094 0.091 0.087

Where Eg is the bandgap of the material and mr is                                                            (La=200A°)

the reduced electron-hole pair mass.
          The main advantages of quantum well                                                                   TableI :the confinement factor for differents
compared to a bulk material are increased material                                                              widths of GaIn0.38 As N0.015 system in GaAs.
gain for equivalent current density, and increased
differential gain.                                                                                         III-2 Effect of width of quantum well and height
          The use of strained QW will further increase                                                     of barrier
the differential gain and reduce the transparency
carrier density [4].                                                                                                 The figure III show the evolution of density
          Our active region consists of two                                                                of current of threshold with the width La of quantum
GaIn0..38 AsN0.015 quantum wells (with a thickness of                                                      well in GaInAsN when the width of confinement
around 7 nm) separated by a 15 nm GaAs barrier.                                                            layer is: 400, 500, and 600 A°.
                                                                                                           It appears that:
                                                                                                            -The density of current has a minimum for La is of
III. Quantum well structure                                                                                value of 40 A° for GaIn0.38 As N0.015 structure. It
                                                                                                           increases when La is higher than 40 A°.
III-1 Effect of width of barrier dconf                                                                      -The structure with dconf=0.04 m , 0.05 m , and
                            -1
                                                                                                           0.06 m has the weakest threshold, which confirms
                      1,0x10                                                                 0
                      9,5x10
                            -2

                            -2
                                                                                   La=80A
                                                                                          0
                                                                                                           the preceding results, the value optimal of thickness
                      9,0x10                                                       La=100A
                      8,5x10
                            -2

                            -2                                                     La=200A
                                                                                          0                dconf can be deduced directly from the variation of
                      8,0x10
                      7,5x10
                            -2

                            -2
                                                                                                           the confinement factor.
                      7,0x10
 Confinement factor




                            -2
                      6,5x10
                            -2
                      6,0x10                                                                                                     1
                      5,5x10
                            -2                                                                                              5,4x10
                      5,0x10
                            -2                                                                                                             dconf=400
                      4,5x10
                            -2
                                                                                                                                 1
                                                                                                                            5,4x10
                                                                                                                                           dconf=500
                      4,0x10
                            -2                                                                                                             dconf=600
                            -2
                      3,5x10
                            -2                                                                                                   1
                      3,0x10                                                                                                5,4x10
                            -2
                      2,5x10
                            -2
                      2,0x10                                                                                                     1
                                                                                                             Jseui(A/cm )




                            -2                                                                                              5,4x10
                                                                                                             2




                      1,5x10
                            -2
                      1,0x10
                            -3
                      5,0x10                                                                                                     1
                                                                                                                            5,4x10
                                  0,0        -8
                                        5,0x10
                                                       -7
                                                  1,0x10    1,5x10
                                                                    -7        -7
                                                                         2,0x10
                                                                                        -7
                                                                                   2,5x10
                                                                                                      -7
                                                                                                 3,0x10
                                                                                                                                 1
                                                                0                                                           5,4x10
                                                       dconf(A )
                                                                                                                                 1
                                                                                                                            5,4x10


          FigureII : the variation of confinement factor
                                                                                                                                 1
                                                                                                                            5,4x10

          in function of dconf thickness of SCH.                                                                                     0,0         -7
                                                                                                                                            5,0x10
                                                                                                                                                           -6     -6       -6     -6    -6    -6     -6
                                                                                                                                                      1,0x10 1,5x10 2,0x10 2,5x10 3,0x10 3,5x10 4,0x10
                                                                                                                                                                       0
                                                                                                                                                                  La(A )

                                                                                                            Figure III : Influence of width of quantum well
The figure II show the influence of dconf thickness                                                          in the density of current of threshold of SCH
of confinement layer adjacent with the                                                                      structure for values of dconf 400,500 and 600 A°.
GaIn0.38 As N0.015 quantum well.
          The confinement factor present a maximum
in function of dconf parameter who is located                                                                       The optimal width of quantum well is
between 400 and 500A° for different thickness of                                                           located in all the cases in the range 40-70A°, the
GaIn0.38 As N0.015 quantum   well   structure.  The                                                        behavior of the density of current of threshold, being
variation of confinement factor is all the more                                                            similar for the tree values studied heights of barrier.
marked that the well is broad.                                                                                      In addition, it appears in figure III that the
                                                                                                           density of current of threshold is all the more weak
                                                                                                           since the height of barrier is less low.
La(A°)                                                20          30           40                50       60                                      -1
                                                                                                                                            2,0x10                                                                 0
                                                                                                                                            1,9x10
                                                                                                                                                  -1
                                                                                                                                                                                                         La=80A
J seuil                                               53.880      53.796 53.775                  53.770 53.770                              1,8x10
                                                                                                                                                  -1
                                                                                                                                                                                                         La=100A
                                                                                                                                                                                                                       0
                                                                                                                                                  -1
                                                                                                                                            1,7x10
(d conf 100 A / cm )                                                                                                                             -1                                                                   0
                                          2                                                                                                 1,6x10                                                       La=200A
                                                                                                                                                  -1
                                                                                                                                            1,5x10




                                                                                                                       Confinement factor
                                                                                                                                                  -1
                                                                                                                                            1,4x10
J seuil                                               53.798      53.777 53.772                  53.773 53.776                              1,3x10
                                                                                                                                                  -1

                                                                                                                                                  -1
                                                                                                                                            1,2x10
(d conf 300 A / cm 2 )
                                                                                                                                                  -1
                                                                                                                                            1,1x10
                                                                                                                                                  -1
                                                                                                                                            1,0x10
                                                                                                                                                  -2
                                                                                                                                            9,0x10
J seuil                                               53.885      53.800 53.779                  53.774 53.775                              8,0x10
                                                                                                                                                  -2

                                                                                                                                                  -2
                                                                                                                                            7,0x10
(d conf  400 A / cm
                                                                                                                                                  -2
                                              2                                                                                             6,0x10
                                                                                                                                                  -2
                                                                                                                                            5,0x10
                                                                                                                                                  -2
                                                                                                                                            4,0x10
                                                                                                                                                  -2
                                                                                                                                            3,0x10
                                                                                                                                                  -2
                                                                                                                                            2,0x10
                                                                                                                                                  -2
                                                                                                                                            1,0x10
                   TableII : The threshold current for differents                                                                                      0,0         -8
                                                                                                                                                              5,0x10
                                                                                                                                                                             -7
                                                                                                                                                                        1,0x10    1,5x10
                                                                                                                                                                                          -7        -7
                                                                                                                                                                                               2,0x10
                                                                                                                                                                                                              -7
                                                                                                                                                                                                         2,5x10
                                                                                                                                                                                                                                -7
                                                                                                                                                                                                                           3,0x10
                   width of GaIn0.38 As N0.015 quatum well system.                                                              FigureV : The variation of confinement factor
                                                                                                                                                      dconf(A )
                                                                                                                                                                                      0



                                                                                                                                in function of dconf thickness of double
                                                                                                                                quantum well .

III-3 Modal gain of SCH structure                                                                                            The figure V show the influence of dconf
                                                                                                                   thickness of confinement layer adjacent with the
                                                                                                                   GaIn0.38 As N0.015 double quantum wells structure.
                                   3
                              1,2x10     Jseuil=53.77(A/cm )
                                                                  2          GaIn0.38AsN0.015
                                                                                                                   Dconf(A°)                           100      200       300       400          500       600               700
   Maxiumum modal gain(cm )
  -1




                                                                                                                   
                                   3
                              1,0x10                                                                                                                   0.023 0.056 0.072 0.075 0.073 0.068 0.063

                                   2
                                                                                                                   (La=80A°)
                              8,0x10

                                                                                                                                                      0.074 0.091 0.094 0.091 0.085 0.078 0.072
                                   2
                              6,0x10                                                                               (La=100A°)

                                   2
                              4,0x10
                                                                                                                                                      0.19     0.18      0.17      0.16         0.14      0.13              0.12
                                                                                                                   (La=200A°)
                                   2
                              2,0x10
                                                  2        2           2        2         2           2        2
                                       1,0x10         1,5x10    2,0x10     2,5x10   3,0x10       3,5x10   4,0x10

                                                               Density of current(A/cm )
                                                                                             2
                                                                                                                                TableVI: the confinement factor for differents
                              FigureVI : the modal gain in function of                                                          widths of GaIn0.38 As N0.015 .
                              desity of current of pumping for the optimized
                              structure.
                                                                                                                           The confinement factor present a maximum
                                                                                                                   in function of dconf parameter who is located
          In figure VI, the modal gain increase with                                                               between 100, 300, and 400A° for different thickness
the density of current of pumping for width of                                                                     of GaIn0.38 As N0.015 double quantum well structure.
quantum well 40 A° for the optimized structure in the                                                              The variation of confinement factor is all the more
precedent paragraphs.                                                                                              marked that the well is broad.
          Morever, the modal gain becomes positive
that for the density of current of threshold.
                                                                                                                   VI-2 Effect of width of double quantum well and

                                       Material                              GaIn0.38 As N0.015                    height of barrier
                                                                                                                            The width optimal of double quantum wells
                                       Gain (cm 1)                         764.95
                                                                                                                   is located in all the cases in the range 20-40 A°, the
                                                                                                                   behavior of the density of current of threshold, being
                                       Jseuil (A/ cm 2 )                    53.77                                  similar for the tree values studied heights of barrier.
                                                                                                                            In addition, it appears in figure VI that the
                                                                                                                   density of current of threshold is all the more weak
                          Table III : the values of maximum gain and                                               since the height of barrier is less low.
                          the threshold current.


VI Double quantum wells structure
VI-1 Effect of width of barrier dconf
                                                                                                                                                          In figure VII, the modal gain increase with
                                      2
                                                                                                                                                the density of current of pumping for width of double
                          1,1x10
                                                                           0
                                                                                                                                                quantum well 20 A° for the optimized structure in the
                                      2             dconf=100A                                                                                  precedent paragraphs.
                          1,1x10                               0
                                                    dconf=300A
                          1,1x10
                                      2             dconf=400A
                                                               0
                                                                                                                                                          Morever, the modal gain becomes positive
                                                                                                                                                that for the density of current of threshold.
                                      2
                          1,1x10
Jseuil(A/cm )
2




                                      2
                          1,1x10

                                      2
                                                                                                                                                        Material             GaIn0.38 As N0.015
                          1,1x10


                          1,1x10
                                      2
                                                                                                                                                        Gain (cm 1)        1200
                                      2
                          1,1x10

                                      2                                                                                                                 Jseuil (A/ cm 2 )   42.77
                          1,1x10
                                              0,0           5,0x10
                                                                  -7
                                                                       1,0x10
                                                                                 -6        -6
                                                                                      1,5x10
                                                                                                     -6
                                                                                                2,0x10    2,5x10
                                                                                                                  -6
                                                                                                                       3,0x10
                                                                                                                              -6
                                                                                                                                   3,5x10
                                                                                                                                           -6


                                                                                                 0
                                                                                          La(A )
                                                                                                                                                  TableVI : values of the maxiumum gain and the
           FigureVI : Influence of width of double quantum                                                                                        current of threshold.
           well in the density of current of threshold of SCH
           structure for values of dconf 100,300 and 400 A°.
                                                                                                                                                V Discussion of results
                                                                                                                                                         This study was to make the optimization of a
                                                                                                                                                laser diode with quantum wells and double quantum
                                                                                                                                                wells with a confinement separated between the
                                                                                                                                                electrons and the photons, first we have calculated
La(A°)                                                       20                  30             40            50                60
                                                                                                                                                the threshold transparensy after having calculated the
J seuil                                                      42.770              42.796 42.610 42.700                           53.770          two-dimensional critical density, for the thickness of
(d conf 100 A / cm 2 )                                                                                                                         active zone and d-conf were calculated and
                                                                                                                                                optimized, the values obtained are:
J seuil                                                      42.774              42.772 42.774 42.778                           42.779
                                                                                                                                                 -40 A° and 400 A° for the thickness of active zone
(d conf 300 A / cm )                               2
                                                                                                                                                and d-conf of GaIn0.38 As N0.015 /GaAs quantum well
J seuil                                                      42.880              42.889 42.800 42.805                           42.810          system.
(d conf  400 A / cm 2 )                                                                                                                         -70A° and 600 A° for the thickness of active zone
                                                                                                                                                and d-conf of GaIn0.38 As N0.015 /GaAs double-quantum
                 TableV : the threshold current for differents                                                                                  wells system.
                 width of GaIn0.38 As N0.015 double quatum wells                                                                                         Thus, the threshold current of 53.77 A/cm 2
                 system.                                                                                                                        of quantum wells and 42.77 A/cm 2 of double-
                                                                                                                                                quantum wells were obtained.
                                                                                                                                                          This analysis enables to conclude that the
VI-3                                 Modal gain of double quantum well                                                                          values of the gain can be made very high and a
                                                                                                                                                minimal threshold current by decreasing the
structure                                                                                                                                       thickness of the active zone and to have a good
                                                                                                                                                optical confinement, i.e. the well of potential shows
                                  5,5x10
                                          3
                                                                                                                                                that the movement of the carriers is quantified.
                                               Jseuil=42.77(A/cm )
                                                                                 2
                                                                                           GaIn0.38AsN0.015                                               In addition, the double-quantum wells
                                          3
                                  5,0x10
                                                                                                                                                structure have been found to be in accordance with
       Maxiumum modal gain(cm )
    -1




                                  4,5x10
                                          3
                                                                                                                                                these results, the most adapted structure for the
                                  4,0x10
                                          3                                                                                                     emission of a laser in (1.3-1.55  m) range based on
                                  3,5x10
                                          3                                                                                                     GaIn0.38 As N0.015 material compared with quantum
                                          3
                                                                                                                                                well structure.
                                  3,0x10
                                                                                                                                                IV Conclusion
                                                                                                                                                          Long-wavelength (1.3-1.55  m)VCSELs
                                          3
                                  2,5x10

                                          3
                                  2,0x10
                                                                                                                                                are the light source for fiber optics networks of the
                                  1,5x10
                                          3

                                                        2              2              2          2          2             2            2
                                                                                                                                                future. GaInAsN/GaAs can replace conventional the
                                              1,0x10          1,5x10           2,0x10     2,5x10     3,0x10        3,5x10       4,0x10
                                                                                                              2
                                                                                                                                                GaInAsP/InPsystem in long-wavelength applications,
                                      Density current(A/cm
                     FigureVII : modal gainofin function) of desity of                                                                          especially for making VCSELs, due to its superior
                     current of pumping for the optimized structure.                                                                            electrical and thermal properties. Our results shows
                                                                                                                                                the importance of number of quantum wells as active
                                                                                                                                                region in VCSELs structure.
Reference
[1]: J. Harris, “Tunable Long-Wavelength Vertical-
Cavity Lasers: The Engine of Next Generation
Optical Networks?” IEEE Journal of Selected Topics
in Quantum Electronics, Vol. 6, No. 6, pg. 1145-
1147, November/December 2000.
[2]: M. Kondow, K. Uomi, A. Niwa, T. Kitatani, S.
Watahiki, Y. Yazawa, “GaInNAs: A Novel Material
for Long-Wavelength-Range Laser Diodes with
Excellent High-Temperature Performance,” Japanese
Journal of Applied Physics, Vol. 35, pp. 1273-1275,
1996.
[3]: J. Harris, S. Spruytte, C. Coldren, M. Larson, M.
Wistey, V. Gambin, W. Ha, “GaInNAs: A New
Material in the Race for Long Wavelength VCSELs,”
Stanford University Agilent Seminar, slide 11,
February 14, 2001.
[4]: L.A. Coldren and S.W. Corzine, “Diode lasers
and Photonic integrated Circuits” John Wiley and
Sons, Chapter 4, 1995.

				
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