# Optical Properties of Silicon

The optical properties of silicon measure at 300K 1. While a wide range of wavelengths is given here, silicon solar cells typical only operate from 400 to 1100 nm. There is a more up to date set of data in Green 2008 2. It is available in tabulated form from pvlighthouse as and in .

Absorption coefficient of silicon in cm-1 as a function of the wavelength. Silicon is an indirect bandgap semiconductor so there is a long tail in absorption out to long wavelengths. The data is graphed on a log scale. The drop in absorption at the band gap (around 1100 nm) is sharper than might first appear. See also absorption coefficient.

The absorption depth is the inverse of the absorption coefficient. An absoption depth of, for example, 1 um means that the light intensity has fallen to 36% (1/e) of its original value. See also absorption coefficient.

The data for the above graph is given below. As noted above, it is also available in a much more convenient Excel spreadsheet.

W - wavelength
a - absorption coefficient
n - real component of refractive index
k - extinction coefficient
refractive index = n - ik

```W(nm)   a(/cm)     n       k
250   1.84E+06   1.694   3.666
260   1.97E+06   1.800   4.072
270   2.18E+06   2.129   4.690
280   2.36E+06   3.052   5.258
290   2.24E+06   4.426   5.160
300   1.73E+06   5.055   4.128
310   1.44E+06   5.074   3.559
320   1.28E+06   5.102   3.269
330   1.17E+06   5.179   3.085
340   1.09E+06   5.293   2.951
350   1.04E+06   5.483   2.904
360   1.02E+06   6.014   2.912
370   6.97E+05   6.863   2.051
380   2.93E+05   6.548   0.885
390   1.50E+05   5.976   0.465
400   9.52E+04   5.587   0.303
410   6.74E+04   5.305   0.220
420   5.00E+04   5.091   0.167
430   3.92E+04   4.925   0.134
440   3.11E+04   4.793   0.109
450   2.55E+04   4.676   0.091
460   2.10E+04   4.577   0.077
470   1.72E+04   4.491   0.064
480   1.48E+04   4.416   0.057
490   1.27E+04   4.348   0.050
500   1.11E+04   4.293   0.045
510   9.70E+03   4.239   0.039
520   8.80E+03   4.192   0.036
530   7.85E+03   4.150   0.033
540   7.05E+03   4.110   0.030
550   6.39E+03   4.077   0.028
560   5.78E+03   4.044   0.026
570   5.32E+03   4.015   0.024
580   4.88E+03   3.986   0.023
590   4.49E+03   3.962   0.021
600   4.14E+03   3.939   0.020
610   3.81E+03   3.916   0.018
620   3.52E+03   3.895   0.017
630   3.27E+03   3.879   0.016
640   3.04E+03   3.861   0.015
650   2.81E+03   3.844   0.015
660   2.58E+03   3.830   0.014
670   2.38E+03   3.815   0.013
680   2.21E+03   3.800   0.012
690   2.05E+03   3.787   0.011
700   1.90E+03   3.774   0.011
710   1.77E+03   3.762   0.011
720   1.66E+03   3.751   0.010
730   1.54E+03   3.741   0.009
740   1.42E+03   3.732   0.008
750   1.30E+03   3.723   0.008
760   1.19E+03   3.714   0.007
770   1.10E+03   3.705   0.007
780   1.01E+03   3.696   0.006
790   9.28E+02   3.688   0.006
800   8.50E+02   3.681   0.005
810   7.75E+02   3.674   0.005
820   7.07E+02   3.668   0.005
830   6.47E+02   3.662   0.004
840   5.91E+02   3.656   0.004
850   5.35E+02   3.650   0.004
860   4.80E+02   3.644   0.003
870   4.32E+02   3.638   0.003
880   3.83E+02   3.632   0.003
890   3.43E+02   3.626   0.002
900   3.06E+02   3.620   0.002
910   2.72E+02   3.614   0.002
920   2.40E+02   3.608   0.002
930   2.10E+02   3.602   0.002
940   1.83E+02   3.597   0.001
950   1.57E+02   3.592   0.001
960   1.34E+02   3.587   0.001
970   1.14E+02   3.582   0.001
980   9.59E+01   3.578   0.001
990   7.92E+01   3.574   0.001
1000   6.40E+01   3.570   0.001
1010   5.11E+01   3.566   -
1020   3.99E+01   3.563   -
1030   3.02E+01   3.560   -
1040   2.26E+01   3.557   -
1050   1.63E+01   3.554   -
1060   1.11E+01   3.551   -
1070   8.00E+00   3.548   -
1080   6.20E+00   3.546   -
1090   4.70E+00   3.544   -
1100   3.50E+00   3.541   -
1110   2.70E+00   3.539   -
1120   2.00E+00   3.537   -
1130   1.50E+00   3.534   -
1140   1.00E+00   3.532   -
1150   6.80E-01   3.530   -
1160   4.20E-01   3.528   -
1170   2.20E-01   3.526   -
1180   6.50E-02   3.524   -
1190   3.60E-02   3.522   -
1200   2.20E-02   3.520   -
1210   1.30E-02   3.528   -
1220   8.20E-03   3.516   -
1230   4.70E-03   3.515   -
1240   2.40E-03   3.513   -
1250   1.00E-03   3.511   -
1260   3.60E-04   3.510   -
1270   2.00E-04   3.508   -
1280   1.20E-04   3.507   -
1290   7.10E-05   3.506   -
1300   4.50E-05   3.504   -
1310   2.70E-05   3.503   -
1320   1.60E-05   3.501   -
1330   8.00E-06   3.500   -
1340   3.50E-06   3.498   -
1350   1.70E-06   3.497   -
1360   1.00E-06   3.496   -
1370   6.70E-07   3.495   -
1380   4.50E-07   3.493   -
1390   2.50E-07   3.492   -
1400   2.00E-07   3.491   -
1410   1.50E-07   3.490   -
1420   8.50E-08   3.489   -
1430   7.70E-08   3.488   -
1440   4.20E-08   3.487   -
1450   3.20E-08   3.486   -

```