|
Arsenic triselenide
Sample preparation
As2Se3 films
were
deposited on silicon substrate by thermal evaporation due to the robust
stoichiometry of bonding in this glass (Pressure < 2.10-5 Torr,
deposition rate ~ 100 Å/s). They were annealed for 2
hours at 180 oC under vacuum before measurements. As
2Se3 glasses were synthesized in our laboratory by Dr.
Mehmet Bayindir and Nicholas Orf.
Measurement and analysis
We performed a three-angle measurement at
72, 75 and 78 degree incident angle. To extract the thickness
of the deposited film, the ellipsometric parameters were fitted
using the Levenberg-Marquardt regression method with a Cauchy-like
dispersion relation:
n=A+B/λ2+c/λ4
k=D/λ+E/λ3+F/λ5
where λ is
the wavelength and A,B,C,D,E,F
are fitting parameters. The deduced dispersion relation was
used to generate starting values in the Levenberg-Marquardt regression
method to calculate the n and k values at every wavelength (independently
of any model).
The standard deviation of the fit was ~ 10-3 and the
corresponding film’s thickness equal to 719 nm. The n-k curves reveal
that the edge of the absorption band due to the material large electronic
bandgap is at ~ 1.83 eV (ref.1). The n values are lower by ~ 2.4%
than the literature values (ref.2), which can be attributed to variations
in the glass stoichiometry and/or in the melting and deposition conditions,
resulting in a different density of the film, and tend to 2.734 in
the infra-red. No significant absorption was measured above 0.9 microns
as sometimes exhibited by chalcogenide glasses between 1 and 6 microns
and 8 and 13 microns due to traces of H2O, H2Se and
other oxide impurities (ref.3).
In addition to measuring the refractive index of As2Se
3 by spectroscopic ellipsometry, we also performed
cutback measurements at 633 nm and 514 nm on films of different thicknesses to
get a precise estimate of the k value and carefully measured the amplitude
and the reproducibility of the metastable
photodarkening effect
by spectroscopic ellipsometry at these two wavelengths.
1. Zallen, R. The physics of amorphous solids, John
Wiley & Sons, 1983
2. Handbook of Optics, Fundamentals, Techniques, &
Design, eds. Bass, M., Stryland, E. W. V., Williams, D. R. &
Wolfe, W. L., McGraw-Hill, INC., 1995
3. Savage, J. A., Optical properties of chalcogenide
glasses Journal of Non-Crystalline Solids 47, 101-116 (1982).
Results
Wavelength
(microns)
|
n
|
k
|
0.25
0.26
0.27
0.28
0.29
0.3
0.31
0.32
0.33
0.34
0.35
0.36
0.37
0.38
0.39
0.4
0.41
0.42
0.43
0.44
0.45
0.46
0.47
0.48
0.49
0.5
0.51
0.52
0.53
0.54
0.55
0.56
0.57
0.58
0.59
0.6
0.61
0.62
0.63
0.64
0.65
0.66
0.67
0.68
0.69
0.7
0.71
0.72
0.73
0.74
0.75
0.76
0.77
0.78
0.79
0.8
0.81
0.82
0.83
0.84
0.85
0.86
0.87
0.88
0.89
0.9
0.91
0.92
0.93
0.94
0.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
1.06
1.07
1.08
1.09
1.1
1.11
1.12
1.13
1.14
1.15
1.16
1.17
1.18
1.19
1.2
1.21
1.22
1.23
1.24
1.25
1.26
1.27
1.28
1.29
1.3
1.31
1.32
1.33
1.34
1.35
1.36
1.37
1.38
1.39
1.4
1.41
1.42
1.43
1.44
1.45
1.46
1.47
1.48
1.49
1.5
1.51
1.52
1.53
1.54
1.55
1.56
1.57
1.58
1.59
1.6
1.61
1.62
1.63
1.64
1.65
1.66
1.67
1.68
1.69
1.7
1.71
1.72
1.73
1.74
1.75
1.76
1.77
1.78
1.79
1.8
1.81
1.82
1.83
1.84
1.85
1.86
1.87
1.88
1.89
1.9
1.91
1.92
1.93
1.94
1.95
1.96
1.97
1.98
1.99
2
2.164
2.346
2.528
2.71
2.892
3.074
3.256
3.438
3.62
3.802
3.984
4.166
4.348
4.53
4.712
4.894
5.076
5.258
5.44
5.622
5.804
5.986
6.168
6.35
6.532
6.714
6.896
7.078
7.26
7.442
7.624
7.806
7.988
8.17
8.352
8.534
8.716
8.898
9.08
9.262
9.444
9.626
9.808
9.99
10.172
10.354
10.536
10.718
10.9
11.082
11.264
11.446
11.628
11.81
11.992
12.174
12.356
12.538
12.72
12.902
13.084
13.266
13.448
13.63
13.812
13.994
14.176
14.358
14.54
14.722
14.904
15.086
15.268
15.45
15.632
15.814
15.996
16.178
16.36
16.542
16.724
16.906
17.088
17.27
17.452
17.634
17.816
17.998
18.18
18.362
18.544
18.726
18.908
19.09
19.272
19.454
19.636
19.818
20
|
2.099
2.135
2.252
2.351
2.463
2.558
2.658
2.750
2.834
2.910
2.984
3.064
3.123
3.181
3.231
3.274
3.314
3.355
3.380
3.416
3.429
3.449
3.460
3.470
3.489
3.490
3.489
3.484
3.485
3.472
3.462
3.440
3.424
3.400
3.381
3.358
3.334
3.310
3.287
3.258
3.240
3.221
3.192
3.164
3.140
3.121
3.107
3.088
3.069
3.050
3.050
3.036
3.027
3.018
3.013
3.001
2.984
2.984
2.973
2.967
2.967
2.962
2.950
2.945
2.945
2.933
2.934
2.927
2.922
2.922
2.916
2.910
2.905
2.902
2.899
2.896
2.896
2.894
2.891
2.886
2.886
2.883
2.881
2.875
2.875
2.873
2.870
2.870
2.867
2.867
2.865
2.865
2.862
2.862
2.859
2.859
2.859
2.859
2.857
2.857
2.854
2.854
2.854
2.851
2.849
2.849
2.849
2.848
2.847
2.848
2.843
2.843
2.843
2.841
2.843
2.841
2.841
2.838
2.838
2.836
2.836
2.833
2.833
2.833
2.833
2.830
2.828
2.828
2.825
2.822
2.822
2.822
2.820
2.817
2.817
2.814
2.814
2.812
2.812
2.812
2.812
2.809
2.808
2.807
2.803
2.802
2.802
2.801
2.799
2.798
2.797
2.795
2.794
2.794
2.792
2.790
2.790
2.787
2.787
2.786
2.784
2.784
2.782
2.782
2.780
2.779
2.778
2.776
2.775
2.773
2.772
2.771
2.770
2.769
2.768
2.768
2.763
2.759
2.755
2.752
2.750
2.748
2.746
2.745
2.744
2.743
2.742
2.741
2.741
2.740
2.740
2.739
2.739
2.738
2.738
2.738
2.737
2.737
2.737
2.737
2.737
2.736
2.736
2.736
2.736
2.736
2.736
2.736
2.735
2.735
2.735
2.735
2.735
2.735
2.735
2.735
2.735
2.735
2.735
2.735
2.735
2.735
2.735
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
2.734
|
1.703
1.766
1.781
1.780
1.769
1.758
1.723
1.688
1.643
1.602
1.555
1.489
1.437
1.382
1.318
1.264
1.208
1.139
1.091
1.012
0.969
0.901
0.852
0.788
0.731
0.678
0.627
0.571
0.523
0.472
0.420
0.353
0.293
0.230
0.168
0.132
0.0954
0.0686
0.0517
0.0361
0.0195
0.0123
0.00715
0.00368
0.00309
0.00261
0.00290
0.00129
0.00189
0.00138
0.000945
0.000845
0.000745
0.000645
0.000545
0.000445
0.000345
0.000215
0.000167
0.000053
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000002
0.000002
0.000002
0.000002
0.000002
0.000002
0.000002
0.000002
0.000002
0.000002
0.000002
0.000002
0.000002
0.000002
0.000002
0.000002
0.000002
0.000002
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0.000001
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000001
0.000001
0.000001
0.000002
0.000003
0.000003
0.000004
0.000005
0.000006
0.000007
0.000008
0.000010
0.000012
0.000013
0.000015
0.000018
0.000020
0.000023
0.000026
0.000029
0.000032
0.000035
0.000039
0.000043
0.000048
0.000052
0.000057
0.000062
0.000068
0.000073
0.000080
0.000086
0.000093
0.000100
|
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