1 Introduction ................................................. 1
2 IR Detector Performance Criteria ............................. 5
2.1 Photon Detectors ........................................ 5
2.1.1 IR detector operating temperature ................ 5
2.1.2 IR detector sensitivity .......................... 7
2.2 Thermal Detectors ....................................... 9
3 IR Detector Materials: A Technology Comparison .............. 13
3.1 Intrinsic Direct Bandgap Semiconductor ................. 13
3.2 Extrinsic Semiconductor ................................ 16
3.3 Quantum Well IR Photodetectors (QWIPs) ................. 18
3.4 Silicon Schottky Barrier Detectors ..................... 23
3.5 High-Temperature Superconductor ........................ 26
3.6 Conclusions ............................................ 27
4 Intrinsic Direct Bandgap Semiconductors ..................... 31
4.1 Minority Carrier Lifetime .............................. 32
4.1.1 Radiative recombination ......................... 32
4.1.2 Auger recombination ............................. 33
4.1.3 Shockley-Read recombination ..................... 34
4.2 Diode Dark Current Models .............................. 34
4.3 Binary Compounds ....................................... 35
4.3.1 Indium antimonide: InSb ......................... 35
4.4 Ternary Alloys ......................................... 37
4.4.1 Mercury cadmium telluride: Hg1-xCdxTe ............ 37
4.5 Pb1-x SnxTe ............................................. 42
4.5.1 Minority carrier lifetime ....................... 43
4.5.2 Dark currents ................................... 44
4.6 Type III Superlattices ................................. 45
4.6.1 Superlattice bandstructure ...................... 45
4.6.2 Band offsets and strain ......................... 47
4.6.3 Interdiffusion in HgTe/CdTe superlattices ....... 48
4.6.4 Misfit dislocations ............................. 48
4.6.5 Absorption coefficient .......................... 49
4.6.6 Effective mass .................................. 51
4.6.7 Minority carrier lifetime ....................... 52
4.7 Type II Superlattices .................................. 53
4.7.1 Minority carrier lifetime ....................... 54
4.8 Direct Bandgap Materials: Conclusions .................. 57
4.8.1 HgCdTe .......................................... 57
4.8.2 InSb ............................................ 57
4.8.3 PbSnTe .......................................... 58
4.8.4 Type III superlattices .......................... 59
4.8.5 Type II superlattices ........................... 59
4.8.6 Final thoughts .................................. 59
5 HgCdTe: Material of Choice for Tactical Systems ............. 61
5.1 HgCdTe Material Properties ............................. 61
5.1.1 Material growth ................................. 61
5.1.2 HgCdTe annealing ................................ 65
5.1.3 HgCdTe properties ............................... 67
5.2 HgCdTe Device Architectures ............................ 75
5.2.1 DLHJ architecture ............................... 76
5.2.2 Bump-bonded ion implant architecture ............ 77
5.2.3 Vertically integrated photodiode (VIP and
HDVIP) architectures ............................ 77
5.3 ROIC Requirements ...................................... 81
5.3.1 Detector performance: Modeling .................. 82
5.3.2 Dark current in HgCdTe diodes ................... 82
5.3.3 1/ƒ noise ....................................... 87
5.4 Detector Performance ................................... 89
5.5 HgCdTe: Conclusions .................................... 91
6 Uncooled Detection .......................................... 93
6.1 Thermal Detection ...................................... 93
6.2 Photon Detection ....................................... 95
6.2.1 HOT detector theory ............................. 95
6.2.2 HOT detector data .............................. 101
6.2.3 HOT detector contacts .......................... 103
6.2.4 HOT detector options ........................... 103
6.3 Uncooled Photon vs. Thermal Detection Limits .......... 105
6.4 Uncooled Detection: Conclusions ....................... 107
7 HgCdTe Electron Avalanche Photodiodes (EAPDs) .............. 109
7.1 Mclntyre's Avalanche Photodiode Model ................. 110
7.2 Physics of HgCdTe EAPDs ............................... 112
7.2.1 High-energy scattering rates ................... 113
7.2.2 Electron impact ionization rate in HgCdTe ...... 115
7.3 Empirical Model for Electron Avalanche Gain in
HgCdTe ................................................ 121
7.4 Room-Temperature HgCdTe APD Performance ............... 129
7.5 Monte Carlo Modeling .................................. 131
7.6 Conclusions ........................................... 133
8 Future HgCdTe Developments ................................. 135
8.1 Dark Current Model .................................... 135
8.1.1 N-side ......................................... 136
8.1.2 P-side ......................................... 137
8.2 The Separate Absorption and Detection Diode
Structure ............................................. 139
8.3 Multicolor and Multispectral FPAs ..................... 141
8.4 High-Density FPAs ..................................... 143
8.5 Low Background Operation .............................. 143
8.5.1 LWIR 14 μm at 40K .............................. 143
8.5.2 Low background operation at a cutoff of 25
μm ............................................. 144
8.6 Higher Operating Temperatures ......................... 145
8.6.1 High-gain APDs ................................. 147
8.7 Conclusion ............................................ 148
Epilogue ...................................................... 149
Appendix A: Mathcad Program for HgCdTe Diode Dark Current
Modeling .......................................... 151
References .................................................... 165
About the Author .............................................. 169
Index ......................................................... 171
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