Arsenic - Selenium - Tellurium alloys

Sample preparation

AsSeTe alloy films were deposited on silicon substrate by thermal evaporation (Pressure < 2.10 -5 Torr, deposition rate ~ 100 Å/s). They were annealed for 2 hours at 180 oC under vacuum before measurements. We studied four different compositions: As40Se50Te 10 , As40Se45Te15, As40Se 40 Te20 and As30Se50Te20, which were synthesized in our laboratory by Dr. Mehmet Bayindir and Nicholas Orf.

Measurement and analysis

We performed a three-angle measurement (at 72, 73 and 74 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 fits were equal to 8.10 -4, 5.10-4, 4.10-4 and 4.10 -4 and the corresponding film’s thicknesses were equal to 198 nm, 277 nm, 230 nm and 840 nm for As40Se50 Te10, As40Se45Te15 , As 40Se40Te20 and As30Se50 Te20, respectively. The n-k curves reveal that the edge of the absorption band due to the material large electronic bandgap is around 1.38 eV, 1.33 eV, 1.22 eV and 0.9 eV for As40Se 50Te10 , As40Se45Te15 , As40Se40T20 and As30Se 50Te20, respectively. No significant absorption was measured above 2 microns.

Results

 

Note: The dispersion relation for As40Se60 is plotted on the graph for comparison (darkest blue curve for n and dark brown curve for k) while the dispersion relation for As30Se50Te20 is only plotted in the two inserts as black dots for clarity. As40Se50 Te10, As40Se45Te15 and As 40Se40Te20 correspond to the three other curves for each n and k, lighter colors corresponding to higher Te contents.
  
 
As40Se50
Te10

As40Se45
Te15

As40Se40
Te20

As30Se50
Te20

Wavelength (microns)
 n k
 Wavelength (microns)
 n
 k
 Wavelength (microns)
 n
 k
 Wavelength (microns)
 n
 k
0.25
 0.264
 0.278
 0.292
 0.306
 0.32
 0.334
 0.348
 0.362
 0.376
 0.39
 0.404
 0.418
 0.432
 0.446
 0.46
 0.474
 0.488
 0.502
 0.516
 0.53
 0.544
 0.5585
 0.574
 0.5895
 0.605
 0.6205
 0.636
 0.6515
 0.667
 0.6825
 0.698
 0.7135
 0.729
 0.7445
 0.76
 0.7755
 0.791
 0.8065
 0.822
 0.8375
 0.853
 0.8685
 0.884
 0.8995
 0.915
 0.9305
 0.946
 0.9615
 0.977
 0.9925
 1.008
 1.0235
 1.039
 1.0545
 1.07
 1.0855
 1.101
 1.1165
 1.132
 1.1475
 1.163
 1.1785
 1.194
 1.2095
 1.225
 1.2405
 1.256
 1.2715
 1.287
 1.3025
 1.318
 1.3335
 1.349
 1.3645
 1.38
 1.3955
 1.411
 1.4265
 1.442
 1.4575
 1.473
 1.4885
 1.504
 1.5195
 1.535
 1.5505
 1.566
 1.5815
 1.597
 1.6125
 1.628
 1.6435
 1.659
 1.6745
 1.69
 1.7055
 1.721
 1.7365
 1.752
 1.7675
 1.783
 1.7985
 1.814
 1.8295
 1.845
 1.8605
 1.876
 1.8915
 1.907
 1.9225
 1.938
 1.9535
 1.969
 1.9845
 2
 1.987
 2.106
 2.253
 2.399
 2.547
 2.681
 2.795
 2.918
 3.033
 3.124
 3.195
 3.264
 3.319
 3.366
 3.406
 3.446
 3.467
 3.466
 3.482
 3.504
 3.516
 3.516
 3.523
 3.510
 3.489
 3.462
 3.433
 3.402
 3.371
 3.341
 3.312
 3.284
 3.258
 3.234
 3.211
 3.190
 3.171
 3.153
 3.136
 3.120
 3.105
 3.092
 3.079
 3.067
 3.056
 3.046
 3.037
 3.028
 3.019
 3.011
 3.004
 2.997
 2.990
 2.984
 2.978
 2.973
 2.968
 2.963
 2.958
 2.954
 2.949
 2.945
 2.942
 2.938
 2.935
 2.931
 2.928
 2.925
 2.923
 2.920
 2.917
 2.915
 2.912
 2.910
 2.908
 2.906
 2.904
 2.902
 2.900
 2.898
 2.897
 2.895
 2.893
 2.892
 2.890
 2.889
 2.888
 2.886
 2.885
 2.884
 2.883
 2.881
 2.880
 2.879
 2.878
 2.877
 2.876
 2.875
 2.874
 2.873
 2.873
 2.872
 2.871
 2.870
 2.869
 2.869
 2.868
 2.867
 2.867
 2.866
 2.865
 2.865
 2.864
 2.863
 2.863
 2.862
1.794
 1.783
 1.796
 1.800
 1.784
 1.748
 1.699
 1.648
 1.559
 1.484
 1.414
 1.341
 1.258
 1.171
 1.098
 1.022
 0.951
 0.878
 0.810
 0.735
 0.664
 0.589
 0.521
 0.439
 0.365
 0.302
 0.249
 0.204
 0.167
 0.136
 0.110
 0.0893
 0.0718
 0.0575
 0.0457
 0.0360
 0.0280
 0.0215
 0.0163
 0.0120
 0.00851
 0.00575
 0.00356
 0.00186
 0.00055
 0.000093
 0.000005
 0.000002
 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
 0
 0
 0
 0
 0
 0
 0
 0
0.25
 0.264
 0.278
 0.292
 0.306
 0.32
 0.334
 0.348
 0.362
 0.376
 0.39
 0.404
 0.418
 0.432
 0.446
 0.46
 0.474
 0.488
 0.502
 0.516
 0.53
 0.544
 0.56
 0.575
 0.59
 0.605
 0.62
 0.635
 0.65
 0.665
 0.68
 0.695
 0.71
 0.725
 0.74
 0.755
 0.77
 0.785
 0.8
 0.815
 0.83
 0.845
 0.86
 0.875
 0.89
 0.905
 0.92
 0.935
 0.95
 0.965
 0.98
 0.995
 1.01
 1.025
 1.04
 1.055
 1.07
 1.085
 1.1
 1.115
 1.13
 1.145
 1.16
 1.175
 1.19
 1.205
 1.22
 1.235
 1.25
 1.265
 1.28
 1.295
 1.31
 1.325
 1.34
 1.355
 1.37
 1.385
 1.4
 1.415
 1.43
 1.445
 1.46
 1.475
 1.49
 1.505
 1.52
 1.535
 1.55
 1.565
 1.58
 1.595
 1.61
 1.625
 1.64
 1.655
 1.67
 1.685
 1.7
 1.715
 1.73
 1.745
 1.76
 1.775
 1.79
 1.805
 1.82
 1.835
 1.85
 1.865
 1.88
 1.895
 1.91
 1.925
 1.94
 1.955
 1.97
 1.985
 2
2.104
 2.066
 2.221
 2.380
 2.523
 2.648
 2.771
 2.892
 3.006
 3.097
 3.181
 3.253
 3.311
 3.369
 3.412
 3.450
 3.480
 3.508
 3.534
 3.538
 3.558
 3.566
 3.572
 3.573
 3.574
 3.566
 3.551
 3.534
 3.506
 3.475
 3.444
 3.412
 3.380
 3.350
 3.321
 3.293
 3.267
 3.242
 3.219
 3.198
 3.178
 3.159
 3.142
 3.126
 3.112
 3.098
 3.086
 3.074
 3.063
 3.054
 3.044
 3.036
 3.028
 3.021
 3.015
 3.008
 3.003
 2.998
 2.993
 2.988
 2.984
 2.980
 2.976
 2.973
 2.970
 2.967
 2.964
 2.961
 2.959
 2.956
 2.954
 2.952
 2.950
 2.948
 2.947
 2.945
 2.943
 2.942
 2.940
 2.939
 2.938
 2.936
 2.935
 2.934
 2.933
 2.932
 2.931
 2.930
 2.929
 2.928
 2.927
 2.926
 2.925
 2.925
 2.924
 2.923
 2.922
 2.922
 2.921
 2.920
 2.920
 2.919
 2.918
 2.918
 2.917
 2.917
 2.916
 2.916
 2.915
 2.914
 2.914
 2.913
 2.913
 2.913
 2.912
 2.912
 2.911
 2.911
 2.910
1.805
 1.821
 1.831
 1.838
 1.815
 1.789
 1.747
 1.692
 1.620
 1.561
 1.490
 1.408
 1.327
 1.257
 1.194
 1.117
 1.056
 0.991
 0.917
 0.852
 0.793
 0.734
 0.655
 0.576
 0.520
 0.458
 0.400
 0.338
 0.282
 0.234
 0.191
 0.154
 0.123
 0.0960
 0.0732
 0.0578
 0.0485
 0.0398
 0.0332
 0.0266
 0.0206
 0.0160
 0.0115
 0.00808
 0.00496
 0.00254
 0.00109
 0.000299
 0.000053
 0.000009
 0.000005
 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
 0
 0
 0
 0
 0
 0
 0
 0
0.25
 0.264
 0.278
 0.292
 0.306
 0.32
 0.334
 0.348
 0.362
 0.376
 0.39
 0.404
 0.418
 0.432
 0.446
 0.46
 0.474
 0.488
 0.502
 0.516
 0.53
 0.544
 0.558
 0.572
 0.586
 0.6
 0.614
 0.628
 0.642
 0.65
 0.6635
 0.677
 0.6905
 0.704
 0.7175
 0.731
 0.7445
 0.758
 0.7715
 0.785
 0.7985
 0.812
 0.8255
 0.839
 0.8525
 0.866
 0.8795
 0.893
 0.9065
 0.92
 0.9335
 0.947
 0.9605
 0.974
 0.9875
 1.001
 1.0145
 1.028
 1.0415
 1.055
 1.0685
 1.082
 1.0955
 1.109
 1.1225
 1.136
 1.1495
 1.163
 1.1765
 1.19
 1.2035
 1.217
 1.2305
 1.244
 1.2575
 1.271
 1.2845
 1.298
 1.3115
 1.325
 1.3385
 1.352
 1.3655
 1.379
 1.3925
 1.406
 1.4195
 1.433
 1.4465
 1.46
 1.4735
 1.487
 1.5005
 1.514
 1.5275
 1.541
 1.5545
 1.568
 1.5815
 1.595
 1.6085
 1.622
 1.6355
 1.649
 1.6625
 1.676
 1.6895
 1.703
 1.7165
 1.73
 1.7435
 1.757
 1.7705
 1.784
 1.7975
 1.811
 1.8245
 1.838
 1.8515
 1.865
 1.8785
 1.892
 1.9055
 1.919
 1.9325
 1.946
 1.9595
 1.973
 1.9865
 2
1.869
 2.064
 2.211
 2.373
 2.523
 2.644
 2.767
 2.883
 3.000
 3.087
 3.173
 3.241
 3.305
 3.351
 3.396
 3.429
 3.454
 3.469
 3.477
 3.476
 3.479
 3.475
 3.479
 3.480
 3.490
 3.506
 3.525
 3.548
 3.558
 3.567
 3.580
 3.575
 3.565
 3.539
 3.504
 3.468
 3.433
 3.402
 3.373
 3.346
 3.321
 3.298
 3.277
 3.257
 3.239
 3.222
 3.207
 3.192
 3.179
 3.167
 3.156
 3.145
 3.135
 3.126
 3.118
 3.110
 3.103
 3.096
 3.090
 3.084
 3.078
 3.073
 3.067
 3.063
 3.058
 3.053
 3.049
 3.044
 3.040
 3.036
 3.032
 3.028
 3.024
 3.020
 3.017
 3.013
 3.009
 3.006
 3.002
 2.999
 2.996
 2.993
 2.990
 2.987
 2.984
 2.982
 2.979
 2.976
 2.974
 2.971
 2.969
 2.966
 2.964
 2.961
 2.959
 2.958
 2.957
 2.956
 2.955
 2.954
 2.953
 2.952
 2.951
 2.951
 2.950
 2.949
 2.949
 2.948
 2.947
 2.947
 2.946
 2.946
 2.946
 2.945
 2.945
 2.945
 2.944
 2.944
 2.944
 2.944
 2.943
 2.943
 2.943
 2.943
 2.943
 2.943
 2.943
 2.943
 2.943
 2.943
1.715
 1.814
 1.818
 1.828
 1.804
 1.784
 1.739
 1.717
 1.647
 1.582
 1.516
 1.434
 1.365
 1.276
 1.215
 1.154
 1.077
 1.009
 0.936
 0.867
 0.838
 0.757
 0.704
 0.650
 0.606
 0.558
 0.521
 0.467
 0.418
 0.397
 0.345
 0.299
 0.247
 0.202
 0.154
 0.118
 0.0953
 0.0751
 0.0634
 0.0532
 0.0448
 0.0396
 0.0333
 0.0275
 0.0219
 0.0184
 0.0137
 0.00973
 0.00720
 0.00488
 0.00289
 0.00183
 0.00120
 0.000851
 0.000572
 0.000356
 0.000185
 0.000054
 0.000009
 0.000005
 0.000002
 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
 0
 0
 0
 0
 0
 0
 0
 0
 0
0.25
 0.2585
 0.267
 0.2755
 0.284
 0.2925
 0.301
 0.3095
 0.318
 0.3265
 0.335
 0.3434
 0.3519
 0.3604
 0.3689
 0.3774
 0.3859
 0.3944
 0.4029
 0.4114
 0.4199
 0.4284
 0.4369
 0.4454
 0.4539
 0.4624
 0.4709
 0.4794
 0.4879
 0.4964
 0.5049
 0.5133
 0.5218
 0.5303
 0.5388
 0.5473
 0.5558
 0.5643
 0.5728
 0.5813
 0.5898
 0.5983
 0.6068
 0.6153
 0.6238
 0.6323
 0.6408
 0.6493
 0.6578
 0.6663
 0.6748
 0.6833
 0.6917
 0.7002
 0.7087
 0.7172
 0.7257
 0.7342
 0.7427
 0.7512
 0.7597
 0.7682
 0.7767
 0.7852
 0.7937
 0.8022
 0.8107
 0.8192
 0.8277
 0.8362
 0.8447
 0.8532
 0.8617
 0.8701
 0.8786
 0.8871
 0.8956
 0.9041
 0.9126
 0.9211
 0.9296
 0.9381
 0.9466
 0.9551
 0.9636
 0.9721
 0.9806
 0.9891
 0.9976
 1.0061
 1.0146
 1.0231
 1.0316
 1.04
 1.0485
 1.057
 1.0655
 1.074
 1.0825
 1.091
 1.0995
 1.108
 1.1165
 1.125
 1.1335
 1.142
 1.1505
 1.159
 1.1675
 1.176
 1.1845
 1.193
 1.2015
 1.21
 1.2184
 1.2269
 1.2354
 1.2439
 1.2524
 1.2609
 1.2694
 1.2779
 1.2864
 1.2949
 1.3034
 1.3119
 1.3204
 1.3289
 1.3374
 1.3459
 1.3544
 1.3629
 1.3714
 1.3799
 1.3884
 1.3968
 1.4053
 1.4138
 1.4223
 1.4308
 1.4393
 1.4478
 1.4563
 1.4648
 1.4733
 1.4818
 1.4903
 1.4988
 1.5073
 1.5158
 1.5243
 1.5328
 1.5413
 1.5498
 1.5583
 1.5667
 1.5752
 1.5837
 1.5922
 1.6007
 1.6092
 1.6177
 1.6262
 1.6347
 1.6432
 1.6517
 1.6602
 1.6687
 1.6772
 1.6857
 1.6942
 1.7027
 1.7112
 1.7197
 1.7282
 1.7367
 1.7451
 1.7536
 1.7621
 1.7706
 1.7791
 1.7876
 1.7961
 1.8046
 1.8131
 1.8216
 1.8301
 1.8386
 1.8471
 1.8556
 1.8641
 1.8726
 1.8811
 1.8896
 1.8981
 1.9066
 1.915
 1.9235
 1.932
 1.9405
 1.949
 1.9575
 1.966
 1.9745
 1.983
 1.9915
 2
 2
 2.18
 2.36
 2.54
 2.72
 2.9
 3.08
 3.26
 3.44
 3.62
 3.8
 3.98
 4.16
 4.34
 4.52
 4.7
 4.88
 5.06
 5.24
 5.42
 5.6
 5.78
 5.96
 6.14
 6.32
 6.5
 6.68
 6.86
 7.04
 7.22
 7.4
 7.58
 7.76
 7.94
 8.12
 8.3
 8.48
 8.66
 8.84
 9.02
 9.2
 9.38
 9.56
 9.74
 9.92
 10.1
 10.28
 10.46
 10.64
 10.82
 11
 11.18
 11.36
 11.54
 11.72
 11.9
 12.08
 12.26
 12.44
 12.62
 12.8
 12.98
 13.16
 13.34
 13.52
 13.7
 13.88
 14.06
 14.24
 14.42
 14.6
 14.78
 14.96
 15.14
 15.32
 15.5
 15.68
 15.86
 16.04
 16.22
 16.4
 16.58
 16.76
 16.94
 17.12
 17.3
 17.48
 17.66
 17.84
 18.02
 18.2
 18.38
 18.56
 18.74
 18.92
 19.1
 19.28
 19.46
 19.64
 19.82
 20
 		1.847
 1.924
 2.024
 2.127
 2.192
 2.278
 2.369
 2.456
 2.540
 2.613
 2.689
 2.765
 2.833
 2.910
 2.973
 3.025
 3.080
 3.126
 3.173
 3.215
 3.247
 3.285
 3.315
 3.345
 3.373
 3.392
 3.413
 3.430
 3.451
 3.461
 3.476
 3.487
 3.495
 3.499
 3.503
 3.513
 3.519
 3.522
 3.524
 3.522
 3.520
 3.515
 3.509
 3.509
 3.503
 3.500
 3.494
 3.484
 3.474
 3.458
 3.444
 3.430
 3.415
 3.397
 3.380
 3.363
 3.346
 3.331
 3.316
 3.302
 3.288
 3.275
 3.263
 3.251
 3.240
 3.229
 3.218
 3.208
 3.199
 3.190
 3.181
 3.173
 3.165
 3.157
 3.149
 3.142
 3.135
 3.129
 3.122
 3.116
 3.110
 3.104
 3.099
 3.093
 3.088
 3.083
 3.078
 3.074
 3.069
 3.065
 3.061
 3.056
 3.052
 3.048
 3.045
 3.041
 3.037
 3.034
 3.031
 3.027
 3.024
 3.021
 3.018
 3.015
 3.012
 3.010
 3.007
 3.004
 3.002
 2.999
 2.997
 2.994
 2.992
 2.990
 2.988
 2.985
 2.983
 2.981
 2.979
 2.977
 2.975
 2.973
 2.972
 2.970
 2.968
 2.966
 2.965
 2.963
 2.961
 2.960
 2.958
 2.956
 2.957
 2.953
 2.951
 2.951
 2.951
 2.948
 2.948
 2.948
 2.946
 2.945
 2.944
 2.942