Enhanced Silicon Light Emission Intensity with Multiple SiGe Quantum

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					Connecting TCAD To Tapeout                                                            A Journal for Process and Device Engineers

                         Enhanced Silicon Light Emission Intensity with
                             Multiple SiGe Quantum Well Structure

      The measured I-V curve from a ten period Si/SiGe
      MQW pin LED fabricated using a UHVCVD system[1]
      is compared with ATLAS simulation results. A sizable
      silicon emission peak is observed at high current injec-
      tion mode at room temperature. This phenomena can
      be explained as follows: because of the hetero-junction
      between the top silicon buffer layer and MQW, when
      bias increases there is a potential barrier formed due to
      band bending. Thus there will be a large accumulation
      of holes in the buffer layer. The recombination rate in
      this layer increases which results in increased silicon
      light intensity.                                                        Figure 1. Sample cross section.

                                                                              for all of the epitaxial layers. After depositing a 25 nm
      The use of silicon germanium (SiGe) for optoelectronic                  undoped Si layer on the n+ substrate, the 10 periods
      components is highly advantageous since SiGe is com-                    consisting of Si/Si0.5Ge0.5 making up the MQW structure
      patible with Si based technologies. Improved growing                    were grown. Each period of the MQW consists of a 3.9
      techniques for heterostructures have also made the                      nm Si0.5Ge0.5 well and a 3nm Si barrier. However, because
      manufacturing of SiGe based devices much easier.                        of the background doping of the UHV-CVD, this region
      Advantages of using SiGe for optoelectronic structures                  was actually lightly p-type doped (NA~1016 cm-3) and de-
      include the low defect density of the material, which                   noted as P- region. After the growth of the MQW, a 24nm
      enhances operation at room temperatures. Also a SiGe                    undoped Si layer was deposited. Finally, a silicon layer
      based device’s operating wavelength can be tuned over                   was deposited on top acting as the buffer layer. The top
      the range of 1.3um to 1.55um making them ideal choices                  layer is heavily doped p-type (NA=1019cm-3) in order to
      for optical fiber communications. Therefore there is wide               form an ohmic contact.
      spread interest in SiGe and SiGe based devices. The de-
      vice studied in this article is a ten period Si/SiGe multi
                                                                              Continued on page 2 ...
      quantum well (MQW) structure. ATLAS is then used to
      simulate the device and the simulated data is compared
      to the measured I-V data. In this way a more physical
      insight into the device operation can be obtained.                         Comparison of 3 Dimensional Quantum
                                                                                  Effect of Nano Device Using BQP
      Preparation                                                                 Model on ATLAS3D................................................ 4
                                                                                 Evaluating of the Avalanche Failure of Power
      The device studied in the article utilizes a p-i-n structure
                                                                                   MOSFETs Using ATLAS .................................... 8
      with a silicon buffer layer. The sample was grown on n-
      Si(001) substrates by a UHV chemical vapor deposition                      Interconnect Parasitic Extraction of BiCMOS
                                                                                   Cell Using Simucad CLEVER .............................. 11
      (UHV-CVD) system at a pressure of 5×10 -9 Torr at 600oC

Volume 16, Number 5, May 2006
      May 2006                                                       Page 1                                                 The Simulation Standard
Figure 2. Simulated (red) and measure (green) IV curve.                Figure 3. Band diagram for the device at zero bias.

The material parameters and the MQW module param-                         nc300=2.8e19 nv300=1.8e19 vsatn=2.4e7
eters used in ATLAS are as following:                                       vsatp=1.775e7 permi=13.95 mun=101.5
mqw ww=0.0039 wb=0.003 nwell=10 nx=5
  ny=240 acceptors=1e16 \                                                 Discussion
    xmin=0 xmax=0.05 ymin=-0.094 ymax=-                                   Figure 1 shows a cross section of the device. Figure 2
  0.022 material=SiGe xcomp=0.5                                           shows the measured and simulated IV curves. Figure 3
material material=silicon EG300=1.12                                      shows the simulated device band diagram at zero bias.
  affinity=4.05 taun0=1e-7 taup0=1e-7                                     The band diagram and corresponding hole distribution
  ni=1e10 \                                                               for three different injection currents are shown in Figure
nc300=2.8e19 nv300=1.8e19 mun=1450                                        4. Figure 5 shows the intensity versus energy for two dif-
  mup=450 vsatn=2.4e7 vsatp=1.65e7 bn=1                                   ferent injection currents. From Figure 5 we see that for low
  bp=0                                                                    injection levels the light intensity has two peaks, one for
                                                                          Si and one for SiGe. Both the peaks are somewhat compa-
material material=sige EG300=0.917
                                                                          rable. As the injection level is increased the peak corre-
  affinity=4.033 taun0=4e-11 taup0=4e-11
                                                                          sponding to SiGe is considerably reduced whilst the peak
  mso=0.1625 ni=1e12 \

Figure 4 The simulation results of band diagram and hole distribution with different currents.

The Simulation Standard                                          Page 2                                                      May 2006
Figure 5. Compared EL intensity (a) injection current=50mA (b) injection current=250mA.

corresponding to the Si material is increased. Even though              light emission is dependent on the radiative recombina-
excellent confinement is achieved by the quantum wells,                 tion and the radiative recombination in turn is propor-
the main component in the optical spectrum at high injec-               tional to the electron - hole product, the Si light emission
tion levels is not from SiGe, as expected, but from Si.                 increases considerably with higher injection currents
                                                                        whilst the SiGe light emission receives little increase.
To try to understand the phenomena simulations were
performed to analyse the electron and hole distributions
in the structure (shown in Figure 6). For initial injec-                Conclusion
tion currents, holes flow into the quantum wells and                    We successfully simulated a MQW SiGe LED which can
are stored in them. This in turn promotes a build up                    enhance Si light emission using ATLAS. This has en-
of the internal electric field at the interface of the QW               abled the underlying physical behaviour of the device to
/ Si buffer regions. This electric field - band bending                 be more thoroughly understood.
forms a barrier to hole flow. Figure 6 shows that the hole
distribution in the quantum well for injection currents                 Reference
of 50mA and 250mA is almost the same, however in the                    [1]   Y. H. Peng, C.H. Hsu, P. S. Chen, M. -J. Tsai, C. H. Kuan, and C. W.
Si buffer region the hole distribution is increased by a                      Liu, Y. W. Suen, “The Electroluminescence Evolution of Ge Quan-
                                                                              tum-Dot Diodes with the Fold Number,” Applied Physics Letters,
factor of almost five for the two injection currents. As the                  Dec. 2004.

Figure 6. Electron and hole distribution.

May 2006                                                       Page 3                                                 The Simulation Standard