Germanium - Arsenic - Selenium - Tellurium alloys 

Sample preparation

GeAsTeSe 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 three different compositions: Ge5As35 Se 50Te10, Ge10As30Se50 Te 10 and Ge15As25Se15Te 45, which were synthesized in our laboratory by Dr. Mehmet Bayindir and Nicholas Orf.

Measurement and analysis

We performed a three-angle measurement: 74, 75 and 76 degrees for Ge5As35Se50 Te 10, 75.5, 76.5 and 77.5 degrees for Ge10 As 30Se50Te10 and 76, 76.5 and 77 degrees for Ge 15As25Se15Te45. 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 3.10 -4, 7.7.10-4 and 3.10-4 and the corresponding film’s thicknesses were equal to 366 nm, 357 nm, and 322 nm for Ge 5As35Se50Te10, Ge10 As30Se50Te10 and Ge15As 25 Se15Te45, respectively

Results

 

Note: Lighter colors correspond to higher Ge content (for k,  from left to right: Ge5As35 Se50Te10, Ge10As30Se50 Te10 and Ge15As25Se15Te 45 ).

   
Ge5 As35
Se50Te10

Ge10 As30
Se50Te10

Ge15 As25
Se15Te45

Wavelength (microns)
 n
 k
 Wavelength (microns)
 n
 k
 Wavelength (microns)
 n
 k
0.25
0.2646
0.2792
0.2938
0.3083
0.3229
0.3375
0.3521
0.3667
0.3813
0.3959
0.4104
0.425
0.4396
0.4542
0.4688
0.4834
0.498
0.5125
0.5271
0.5417
0.5563
0.5709
0.5855
0.6001
0.6146
0.6292
0.6438
0.6584
0.673
0.6876
0.7021
0.7167
0.7313
0.7459
0.7605
0.7751
0.7897
0.8042
0.8188
0.8334
0.848
0.8626
0.8772
0.8918
0.9063
0.9209
0.9355
0.9501
0.9647
0.9793
0.9939
1.0084
1.023
1.0376
1.0522
1.0668
1.0814
1.096
1.1105
1.1251
1.1397
1.1543
1.1689
1.1835
1.1981
1.2126
1.2272
1.2418
1.2564
1.271
1.2856
1.3002
1.3147
1.3293
1.3439
1.3585
1.3731
1.3877
1.4023
1.4168
1.4314
1.446
1.4606
1.4752
1.4898
1.5044
1.5189
1.5335
1.5481
1.5627
1.5773
1.5919
1.6064
1.621
1.6356
1.6502
1.6648
1.6794
1.694
1.7085
1.7231
1.7377
1.7523
1.7669
1.7815
1.7961
1.8106
1.8252
1.8398
1.8544
1.869
1.8836
1.8982
1.9127
1.9273
1.9419
1.9565
 2.067
2.149
2.294
2.448
2.584
2.705
2.823
2.933
3.032
3.110
3.180
3.239
3.287
3.325
3.355
3.377
3.395
3.407
3.411
3.411
3.404
3.395
3.381
3.367
3.346
3.322
3.293
3.267
3.238
3.211
3.186
3.164
3.143
3.123
3.106
3.089
3.073
3.059
3.046
3.033
3.021
3.010
3.000
2.990
2.981
2.972
2.964
2.956
2.949
2.942
2.936
2.929
2.924
2.918
2.913
2.908
2.903
2.898
2.894
2.889
2.885
2.882
2.878
2.874
2.871
2.868
2.865
2.862
2.859
2.856
2.853
2.851
2.849
2.846
2.844
2.842
2.840
2.838
2.836
2.834
2.832
2.830
2.828
2.827
2.825
2.824
2.822
2.821
2.819
2.818
2.816
2.815
2.814
2.813
2.812
2.810
2.809
2.808
2.807
2.806
2.805
2.804
2.803
2.802
2.801
2.801
2.800
2.799
2.798
2.797
2.796
2.796
2.795
2.794
2.794
2.793
2.792
2.792
 1.674
1.717
1.727
1.708
1.677
1.636
1.578
1.513
1.434
1.359
1.273
1.189
1.112
1.032
0.952
0.871
0.780
0.700
0.630
0.550
0.479
0.403
0.342
0.291
0.248
0.212
0.181
0.155
0.133
0.114
0.0975
0.0838
0.0720
0.0620
0.0534
0.0460
0.0397
0.0342
0.0296
0.0256
0.0222
0.0192
0.0167
0.0146
0.0128
0.0112
0.00993
0.00882
0.00789
0.00712
0.00648
0.00595
0.00553
0.00519
0.00492
0.00472
0.00458
0.00448
0.00442
0.00440
0.00440
0.00444
0.00449
0.00436
0.00425
0.00415
0.00406
0.00397
0.00380
0.00322
0.00259
0.00188
0.00151
0.00126
0.000954
0.000703
0.000342
0.000174
0.000085
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
0.2638
0.2776
0.2914
0.3052
0.319
0.3328
0.3466
0.3604
0.3742
0.388
0.4018
0.4156
0.4294
0.4432
0.4571
0.4709
0.4847
0.4985
0.5123
0.5261
0.5399
0.5537
0.5675
0.5813
0.5951
0.6089
0.6227
0.6365
0.6503
0.6641
0.6779
0.6917
0.7055
0.7193
0.7331
0.7469
0.7607
0.7745
0.7883
0.8021
0.8159
0.8297
0.8435
0.8574
0.8712
0.885
0.8988
0.9126
0.9264
0.9402
0.954
0.9678
0.9816
0.9954
1.0092
1.023
1.0368
1.0506
1.0644
1.0782
1.092
1.1058
1.1196
1.1334
1.1472
1.161
1.1748
1.1886
1.2024
1.2162
1.23
1.2438
1.2577
1.2715
1.2853
1.2991
1.3129
1.3267
1.3405
1.3543
1.3681
1.3819
1.3957
1.4095
1.4233
1.4371
1.4509
1.4647
1.4785
1.4923
1.5061
1.5199
1.5337
1.5475
1.5613
1.5751
1.5889
1.6027
1.6165
1.6303
1.6441
1.6579
1.6718
1.6856
1.6994
1.7132
1.727
1.7408
1.7546
1.7684
1.7822
1.796
1.8098
1.8236
1.8374
1.8512
1.865
 1.499
1.517
1.607
1.710
1.796
1.874
1.962
2.046
2.123
2.200
2.270
2.336
2.401
2.458
2.518
2.565
2.619
2.662
2.704
2.756
2.808
2.852
2.887
2.908
2.912
2.892
2.847
2.805
2.813
2.917
3.034
3.049
3.025
3.003
2.982
2.964
2.946
2.931
2.916
2.903
2.891
2.879
2.869
2.859
2.850
2.841
2.833
2.826
2.819
2.813
2.807
2.801
2.796
2.792
2.789
2.785
2.780
2.780
2.776
2.774
2.773
2.770
2.770
2.768
2.766
2.764
2.764
2.763
2.760
2.761
2.760
2.757
2.755
2.754
2.753
2.753
2.752
2.751
2.749
2.748
2.748
2.747
2.746
2.744
2.744
2.743
2.743
2.742
2.743
2.742
2.741
2.741
2.740
2.738
2.738
2.738
2.736
2.736
2.735
2.735
2.735
2.734
2.733
2.734
2.732
2.730
2.730
2.731
2.731
2.731
2.731
2.731
2.730
2.730
2.728
2.728
2.728
2.728
 1.292
1.300
1.339
1.364
1.381
1.389
1.395
1.393
1.381
1.366
1.346
1.325
1.298
1.268
1.236
1.204
1.163
1.123
1.070
1.025
0.983
0.927
0.878
0.829
0.772
0.723
0.702
0.695
0.660
0.625
0.548
0.365
0.163
0.116
0.101
0.0845
0.0686
0.0573
0.0482
0.0346
0.0278
0.0187
0.0119
0.00958
0.00731
0.00731
0.00731
0.00504
0.00504
0.00504
0.00504
0.00731
0.00504
0.00504
0.00731
0.00731
0.00731
0.00731
0.00504
0.00277
0.00504
0.00277
0.00277
0.00277
0.00277
0.00277
0.00277
0.00504
0.00504
0.00958
0.00731
0.00731
0.00731
0.00504
0.00504
0.00504
0.00504
0.00504
0.00277
0.00277
0.00504
0.00731
0.00504
0.00277
0.001123
0.000731
0.000384
0.000095
0.000054
0.000021
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
 0.25
0.268
0.286
0.304
0.322
0.34
0.358
0.376
0.394
0.412
0.43
0.448
0.466
0.484
0.502
0.52
0.538
0.556
0.574
0.592
0.61
0.628
0.646
0.664
0.682
0.7
0.718
0.736
0.754
0.772
0.79
0.808
0.826
0.844
0.862
0.88
0.898
0.916
0.934
0.952
0.97
0.988
1.006
1.024
1.042
1.06
1.078
1.096
1.114
1.132
1.15
1.168
1.186
1.204
1.222
1.24
1.258
1.276
1.294
1.312
1.33
1.348
1.366
1.384
1.402
1.42
1.438
1.456
1.474
1.492
1.51
1.528
1.546
1.564
1.582
1.6
1.618
1.636
1.654
1.672
1.69
1.708
1.726
1.744
1.762
1.78
1.798
1.816
1.834
1.852
1.87
1.888
1.906
1.924
1.942
1.96
1.978
1.996

 1.758
1.779
1.950
2.093
2.250
2.404
2.545
2.706
2.842
2.969
3.082
3.194
3.293
3.388
3.463
3.529
3.596
3.647
3.714
3.755
3.793
3.832
3.863
3.890
3.919
3.939
3.944
3.938
3.925
3.912
3.913
3.928
3.947
3.966
4.006
4.016
3.866
3.764
3.706
3.651
3.607
3.584
3.591
3.620
3.661
3.702
3.743
3.780
3.824
3.836
3.844
3.789
3.762
3.717
3.645
3.585
3.526
3.477
3.440
3.409
3.382
3.367
3.363
3.350
3.348
3.343
3.337
3.336
3.336
3.336
3.336
3.336
3.336
3.332
3.332
3.332
3.328
3.328
3.324
3.324
3.324
3.324
3.324
3.324
3.324
3.324
3.324
3.324
3.324
3.324
3.324
3.324
3.324
3.324
3.320
3.320
3.316
3.316

 1.673
1.823
1.892
1.945
1.974
1.985
1.994
1.979
1.948
1.916
1.869
1.811
1.752
1.681
1.620
1.556
1.481
1.420
1.324
1.263
1.194
1.123
1.069
1.003
0.928
0.852
0.783
0.719
0.665
0.628
0.595
0.561
0.524
0.480
0.408
0.313
0.126
0.098
0.127
0.165
0.173
0.214
0.266
0.298
0.301
0.296
0.274
0.239
0.205
0.178
0.163
0.152
0.140
0.133
0.129
0.118
0.106
0.102
0.0910
0.0758
0.0606
0.0488
0.0160
0.00342
0.000904
0.0001615
0.000052
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