Report on PL Kriteshwar Kohli, Gordon Davies, King s College London by armedman1

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									     Report on PL
Kriteshwar Kohli, Gordon Davies,
      King’s College London
           Technical details

• Samples irradiated with 1e12 to 3e16 cm-2
• Etched in HF:water 1:20 for ~20 mins, RT,
  to give surface finish visually like highly
  polished Si surface
• Measured at ~4 K, in liquid helium, looking
  at top few micrometres.
• As-received, and annealed at 80 C & 450 C.
                                                                                                             -1
                                             3 e1 4 , A nn e ale d a t 80 C for 2 4 h rs ( to tal ), 4 c m
                  6 00
                                       789.51168


                  5 00



                  4 00
PL In ten s ity




                  3 00                                              1018.326



                  2 00



                  1 00



                    0


                         6 00   70 0      8 00          90 0        10 00      11 00        12 00

                                                 P h oto n E ne rg y m e V




Example: 789 meV = CiOi, 1018 meV = W (3I ?)
            The technique
• High energy resolution : unique defect
  characterisation for sharp lines...
• …but broad band PL is not identified.
• PL must be seen…
• …defects may be non-radiative (VV) or PL
  quenched by other defects.
            Annealing data
• 7 different fluences (1e12 to 3e16 cm-2)
• Spectra as received and 4 anneals at 80 C
  and one at 450 C
• 42 spectra

• Sample spectra only here
                                         Recovery at 80 C (4 mins)
                                                                                         -1                                                                                                                                  -1
                                                                           3 e1 4 , 4 c m , no a n ne a l                                                               3 e 14 , A n ne al ed at 80 C for 4 m i ns , 4 c m
                   20                                                                                                           75
                                                                                                                                                    789.51168


                                      789.51168
                                                                                                                                50
P L In ten s ity




                                                                                                            P L In te ns i ty
                   10


                                                                                                                                25




                                                                                                                                 0
                    0




                                                                                                                                -25
                        6 00   7 00      8 00        9 00       10 0 0       11 00       12 00                                        60 0   70 0      80 0          900       1 00 0      1 10 0      12 00

                                            P h oto n E ne rg y ( m e V)                                                                                      P ho ton En er gy m e V




                                3e14 cm-2 no anneal                                                                                   3e14 cm-2 annealed 4 mins
                   All samples : No change in spectral shape
                                     Recovery at 80 C (30 mins)
                                                                                                                                                                                                                                -1
                                                                                        -1                                                                    1e 1 3, An n ea le d a t 8 0 C fo r 3 0 m ins ( to tal ), 4 c m
                                                                          1 e1 3, 4 c m , n o a n ne al
                    6
                                                                                                                              1 80                 789.51168
                                     789.51168
                                                                                                                              1 60

                                                                                                                              1 40
                    4
                                                                                                                              1 20




                                                                                                          P L In te n s ity
P L In te n s ity




                                                                                                                              1 00                                                       1096.994 48

                                                                                                                               80
                    2
                                                                                                                               60
                                                                           1092.45663
                                                                                                                               40
                                                                                                                                                                            969.3147 3
                                                                                                                                                                                 1018.326       1149.83689
                                                                                                                               20
                    0
                                                                                                                                0

                                                                                                                              -20
                        60 0   700      80 0          9 00       1 00 0        1 10 0        1 20 0                                  60 0   70 0      80 0           90 0       1 00 0       1 10 0       1 20 0

                                               P ho to n E n er gy m e V                                                                                     P ho ton En e rg y m eV




                               1e14 cm-2 no anneal                                                                                     1e14 cm-2 annealed 30 mins
Lower fluences : Recovery of shallow PL, observation of C iCs
and W
                                        Recovery at 80 C (12 hrs)
                                                                                                              -1                                                                                                                 -1
                                           1e 1 2, An n ea le d a t 8 0 C fo r 1 2 h ou rs (to tal) , 4 c m                                                   1e 1 4, An n ea le d a t 8 0C fo r 1 2 h ou rs (to ta l) , 4 c m
                    20                                                                                                               40
                                                                            1096.99448
                    18                                                                                                                                  789.51168

                    16
                                                                                                                                     30
                    14

                    12




                                                                                                                   PL In ten s ity
P L In te n s ity




                    10                                                                                                               20
                                                                                                                                                                                   101 8.09043
                     8

                     6
                                                                                                                                     10
                     4                                                            1149.83689
                                       789.5 1168
                     2
                                                                                                                                      0
                     0

                    -2
                         6 00   7 00      8 00          9 00       1 00 0      11 0 0      12 0 0                                         600    7 00      8 00          9 00       1 00 0     11 0 0       12 00

                                                 Ph oto n E n er gy m e V                                                                                         Ph o to n E n er gy m e V




                    1e12 cm-2 annealed 12 hrs                                                                                                   1e14 cm-2 annealed 12 hrs

                    Lowest dose: almost complete                                                                                                Higher fluences: CiOi
                    recovery.                                                                                                                   and W but 1e16, 3e16
                                                                                                                                                no change
                                           Recovery at 80 C (24 hrs)
                                                                                                                       -1                                                                                                                  -1
                                                       1 e1 3, A nn e ale d a t 8 0 C for 2 4 h rs ( to tal ), 4 c m                                                     3 e1 6 , A nn ea le d a t 8 0 C fo r 2 4 h rs (to ta l) , 4 c m
                                                                                                                                                60
                  1 00
                                                                                                                                                                                                 1018.326
                                       7 89 .5 11 68                                                                                            50
                   80

                                                                                                                                                40
                                                                                                                                                                    790.70194




                                                                                                                            P L In ten s ity
                   60
PL In ten s ity




                                                                                                                                                30


                   40                                                                                                                           20



                                                                                                                                                10
                   20
                                                                                  1 09 2. 44 42 3
                                                                       1 01 8.0 9 04 3
                                                                                                                                                 0

                    0
                                                                                                                                               -1 0
                                                                                                                                                      6 00   70 0      80 0          90 0       1 00 0       1 10 0        1 20 0
                         6 00   70 0       8 00            90 0         10 00         11 00         12 00
                                                                                                                                                                              P ho ton En e rg y m eV
                                                  P h oto n E ne rg y m e V




                     1e13 cm-2 annealed 24 hrs                                                                                                               3e16 cm-2 annealed 24 hrs
                  CiCs and W , with ratio of PL from W and C iCs increasing with
                  fluence especially at the highest doses.
                                Anneal at 450 C (30 mins)
                                                                                                                                                                                       -1                                                                                                                                                      -1
                                                                                     1 e 14 , a nn e al ed a t 45 0C fo r 3 0 m i n, 4c m                                                                                              3 e1 6, an n ea le d a t 4 50 C fo r 30 m in , 4c m




                                                                                                                          9 91 .3 09 67
                                                                                                                                                                                                              6 00



                                                                                                                                                                                                              5 00
                                                         7 67 .2 68 77




                                                                                                                                                                                                              4 00
P L In te n s ity




                                                                                                                                                                                            PL In ten s ity
                    50

                                                                                                         97 0. 98 85 28                                                                                       3 00




                                                                                                                                                                                                                                                                9 91 .3 09 67
                                                                                                                                   1 00 3. 49 73 9
                                       7 53 .40 72 5 1




                                                                                                                                                     10 39 .8 49 8
                                                                         78 9. 51 16 8




                                                                                                                                                                                                                                                                                10 39 .6 01 83
                                                                                                                                                                                                              2 00




                                                                                                                                                                                                                                                                                                   1 1 01 .06 1 19
                                                                                                                                                                                                                                                                                                                     11 27 .5 93 98
                                                                                                                                                                                                              1 00


                     0
                                                                                                                                                                                                                0


                         6 00   70 0                                     80 0                   90 0               1 0 00                                            1 10 0   1 20 0                                 6 00     70 0   80 0          90 0        10 00                             11 00                                1 2 00

                                                                                         P h oton En e rg y m eV                                                                                                                            P h oto n E ne rg y m e V




1e14 cm-2 and below: broad                                                                                                                                                                                                  3e14 cm-2 and above: broad
band gone                                                                                                                                                                                                                   band persists at increasing
                                                                                                                                                                                                                            expense of sharp lines.
                                                                                                                                                                                                                            Shown is 3e16 cm-2
        Summary of annealing
• As received: low PL intensity, CiOi plus broad
  band
• At 80 C, no change in bandshapes after 4 mins.
• After 30 mins, start of observing weak CiCs and
  W; W continues to increase after 12 hrs and 24
  hrs.
• After 450 C, ‘point defects’ to 1e14 cm-2;
  increasing dominance of broad band at higher
  fluences.
     Problems: 1. Quenching
• From ion-implantation at nominal RT, PL is
  quenched when the mean distance between
  VVs is less than ~50 atoms.
• Assume production rate for VV of 1.3 cm-1.
• At maximum fluence, 3e16 cm-3, the mean
  VV separation is 110 atoms.
• Implies quenching is not important.
      Problems: 2. Mobility of C

•   Cs + I --> Ci Ci + Oi --> CiOi
•   Thermal diffusion of Ci is
•   D = 0.44 exp (-870 meV/kT ) cm2 s-1 , so
•   Random walk in 1 second is by 2e-8 cm at 20 C
•   and by 2e-6 cm at 100 C.
•   Compare: mean separation of carbon of 7e-6 cm.
•   Infra-red absorption data?
                         Carbon interstitials : PL at 856 meV
                           No evidence in as-irradiated state

                                                                                       -1
                                                                        1 e1 5, 4 c m , n o a n ne al


                                       789.51168
                    10
P L In te n s ity




                     5




                     0




                         6 00   7 00      8 00          90 0        10 00      11 00        12 00

                                                 P h oto n E ne rg y m e V
   Problems: 3. Carbon content
• Assume production rates for VV of 1.3 cm-
  1, and VO of 0.7 cm-1 . Possibly for I, R =

  0.7 cm-1 , and for I2 = 1.3 cm-1 ?
• [C] < 2.5e15 cm-3 from SIMS.
• At dose > 3e15 cm-2 , I’s exceed [C]
• Cs + I --> Ci Ci + Oi --> CiOi
• CiOi + I --> ICiOi      (Destruction of CiOi )
                                                           789_4mins

                        20

                        18
                                                                Estimate [C]
                        16

                        14
                                                                from CiOi
                        12
         PL Intensity

                        10

                        8

                        6

                        4

                        2

                        0

                             1E12   1E13   1E14   1E15   1E16
                                           Dose



For 2 MeV electrons, peak 789 meV is when creation of I’s is
0.75 [C]. For a production rate of R = 0.7 cm-1 , peak at (5 to 6)
e14 cm-2 implies [C] ~5e14 cm-3 .
                                                                969_12hrs


                     0.30
                                   unreliable
                     0.25
                                                          Estimate [C] from CiCs
                     0.20
      PL Intensity



                     0.15


                     0.10


                     0.05


                     0.00


                            1E12     1E13       1E14   1E15   1E16
                                                Dose


For 2 MeV electrons, peak 969 meV with [C]<<[O] is when
creation of I’s is ~0.25 [C]. For a production rate of R = 0.7
cm-1 , peak at 2e14 cm-2 implies [C] = 6e14 cm-3 .
           Questions arising
• What is the production rate R of isolated
  I’s?
• Using data from 2 MeV electron
  irradiations at 100 C, with R = 0.7 cm-1 , the
  predicted [C] values are ~5e14 cm-3 , lower
  than SIMS.
• What is the mobility of Ci during the
  irradiations?

								
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