Mercury Cadmium Telluride: Growth, Properties and Applications (Wiley Series in Materials for Electronic & Optoelectronic Applications)

Mercury cadmium telluride (MCT) is the third most well-regarded semiconductor after silicon and gallium arsenide and is the material of choice for use in infrared sensing and imaging. The reason for this is that MCT can be 'tuned' to the desired IR wavelength by varying the cadmium concentration. Mercury Cadmium Telluride: Growth, Properties and Applications provides both an introduction for newcomers, and a comprehensive review of this fascinating material. Part One discusses the history and current status of both bulk and epitaxial growth techniques, Part Two is concerned with the wide range of properties of MCT, and Part Three covers the various device types that have been developed using MCT. Each chapter opens with some historical background and theory before presenting current research. Coverage includes: Bulk growth and properties of MCT and CdZnTe for MCT epitaxial growth Liquid phase epitaxy (LPE) growth Metal-organic vapour phase epitaxy (MOVPE) Molecular beam epitaxy (MBE) Alternative substrates Mechanical, thermal and optical properties of MCT Defects, diffusion, doping and annealing Dry device processing Photoconductive and photovoltaic detectors Avalanche photodiode detectors Room-temperature IR detectors Mercury Cadmium Telluride......Page 5 Contents......Page 9 Series Preface......Page 23 Preface......Page 25 Foreword......Page 29 List of Contributors......Page 33 Part One - Growth......Page 37 1.1 Introduction......Page 39 1.2 Phase equilibria......Page 40 1.3 Crystal growth......Page 41 1.3.1 Solid state recrystallization (SSR)......Page 42 1.3.2 Traveling heater method (THM)......Page 45 1.3.3 Bridgman......Page 48 1.3.4 Accelerated crucible rotation technique (ACRT)......Page 49 1.4 Conclusions......Page 54 References......Page 55 2.1 Introduction......Page 57 2.2.1 Cadmium......Page 58 2.3.1 Polycrystal growth......Page 59 2.3.2 VGF single-crystal growth......Page 60 2.4 Wafer processing......Page 77 2.4.1 Process flow......Page 78 2.4.2 Characteristics......Page 80 Acknowledgements......Page 84 References......Page 85 3 Properties of Cd(Zn)Te Relevant to Use as Substrates......Page 87 3.2.1 Ionicity......Page 88 3.2.2 Lattice constant and crystal density......Page 89 3.2.3 Spontaneous ordering......Page 90 3.3.1 Phase diagram......Page 91 3.3.2 Specific heat and Debye temperature......Page 92 3.3.4 Thermal conductivity and diffusivity......Page 93 3.4.2 Microhardness......Page 94 3.4.3 Optical phonon frequency and phonon deformation potential......Page 95 3.5.2 Fröhlich coupling constant......Page 97 3.6.1 Bandgap energy......Page 98 3.6.2 Electron and hole effective masses......Page 100 3.6.3 Electronic deformation potential......Page 101 3.6.4 Heterojunction band offset......Page 102 3.7.1 The reststrahlen region......Page 103 3.7.2 The interband transition region......Page 104 3.7.3 Near or below the fundamental absorption edge......Page 105 3.8.1 Low-field mobility......Page 106 References......Page 107 4 Substrates for the Epitaxial Growth of MCT......Page 111 4.1 Introduction......Page 112 4.2 Substrate orientation......Page 113 4.3.1 Effects of poor thermal conductivity on MCT growth......Page 114 4.3.2 Effects of substrate crystalline defects on MCT growth......Page 115 4.3.4 Effects of nonuniform substrate composition and substrate roughness......Page 116 4.3.6 Characterization and screening of CZT substrates......Page 117 4.4 Si-based substrates......Page 118 4.4.1 Nucleation and growth of CdTe on Si......Page 119 4.4.2 The effects of As and Te monolayers......Page 120 4.4.3 Advantages of CdTe/Si substrates......Page 121 4.4.4 Disadvantages of CdTe/Si substrates......Page 122 4.4.5 Reduction of the dislocation density......Page 123 4.4.6 Passivation of dislocations......Page 124 4.5 Other substrates......Page 125 References......Page 126 5.1 Introduction......Page 131 5.2.1 Introduction......Page 132 5.2.3 LPE growth techniques......Page 134 5.3.1 Composition and thickness......Page 139 5.3.2 Crystal quality and surface morphology......Page 141 5.3.3 Impurity doping and electrical properties......Page 142 5.5 Summary and future developments......Page 144 References......Page 146 6.1 Requirement for epitaxy......Page 149 6.2 History......Page 150 6.3.1 Orientation......Page 151 6.3.2 Material......Page 152 6.4 Reactor design......Page 153 6.5 Process parameters......Page 154 6.6 Metal-organic sources......Page 155 6.8 Reproducibility......Page 156 6.9 Doping......Page 159 6.10 Defects......Page 161 6.12 In situ monitoring......Page 163 References......Page 164 7.1 Introduction......Page 167 7.2 MBE Growth theory and growth modes......Page 168 7.2.2 Quasiequilibrium theories......Page 169 7.2.3 Kinetic theories......Page 170 7.4.1 Reflection high-energy electron diffraction......Page 171 7.4.2 Spectroscopic ellipsometry......Page 172 7.5 MCT nucleation and growth......Page 175 7.6 Dopants and dopant activation......Page 177 7.7.1 Electrical properties......Page 179 7.7.3 Structural properties......Page 180 7.7.4 Surface defects......Page 181 7.8 Conclusions......Page 182 References......Page 183 Part Two - Properties......Page 187 8 Mechanical and Thermal Properties......Page 189 8.1.2 Variation of density with x......Page 190 8.1.3 Variation of density with temperature......Page 191 8.2.2 Variation of lattice parameter with x......Page 194 8.2.3 Variation with temperature......Page 196 8.3.2 Variation with x......Page 198 8.3.3 Variation with temperature......Page 199 8.4.1 Introduction......Page 202 8.4.2 Elastic parameter values......Page 203 8.5.2 Hardness......Page 206 8.5.3 Deformation characteristics of MCT......Page 210 8.5.5 Conclusion......Page 216 8.6.3 Solid phases......Page 217 8.6.4 Quasibinary systems......Page 219 8.6.5 Liquidus, solidus, and solvus surfaces......Page 221 8.6.6 Thermodynamics......Page 222 8.7.2 Temperature variation of kinematic viscosity of the MCT melt......Page 223 8.8.2 Specific heat (Cp)......Page 225 8.8.3 Thermal diffusivity (Dθ)......Page 228 8.8.4 Thermal conductivity (Kθ)......Page 230 References......Page 233 9.1 Introduction......Page 241 9.3 Theory of band to band optical transition......Page 242 9.4 Near band gap absorption......Page 243 9.5 Analytic expressions and empirical formulas for intrinsic absorption and Urbach tail......Page 245 9.6 Dispersion of the refractive index......Page 252 9.7 Optical constants and related van Hover singularities above the energy gap......Page 253 9.8 Reflection spectra and dielectric function......Page 256 9.9 Multimode model of lattice vibration......Page 257 9.10 Phonon absorption......Page 258 9.11 Raman scattering......Page 261 9.12 Photoluminescence spectroscopy......Page 263 References......Page 267 10.1 Introduction......Page 275 10.2 Self-diffusion......Page 276 10.2.3 Te self-diffusion......Page 277 10.2.5 Conclusions......Page 278 10.3.1 Composition: xCd ~ 0.2......Page 279 10.3.3 Cadmium telluride (CdTe)......Page 281 10.3.4 Conclusions......Page 282 10.4 Compositional interdiffusion......Page 283 10.4.1 D from CID profiles of xCd versus x......Page 284 10.4.2 Conclusions......Page 288 10.5 Impurity diffusion......Page 289 10.5.1 Group 1 impurities......Page 290 10.5.2 Group 3 and 5 impurities......Page 292 10.5.3 Group 6 and 7 impurities......Page 294 References......Page 296 11.1 Introduction......Page 299 11.2 Native point defects in zincblende semiconductor......Page 300 11.3 Measurement of native defect properties and density......Page 302 11.4.1 Defect formation energies......Page 304 11.4.2 Electronic excitation energies......Page 305 11.4.4 Prediction of native point defect densities in HgCdgTe......Page 306 References......Page 308 12.1 Introduction......Page 311 12.2.2 Valence band offset......Page 313 12.3.1 k·p theory......Page 315 12.3.2 Hybrid pseudopotential tight-binding method......Page 317 12.4.1 Optical absorption......Page 324 12.4.2 Auger recombination......Page 325 References......Page 329 13.1 Introduction......Page 333 13.2 Native defects in undoped MCT......Page 334 13.3 Native defects in doped MCT......Page 337 13.4 Defect concentrations during cool down......Page 338 13.5.1 CTC by thermal annealing......Page 340 13.6.1 IBM of vacancy-doped MCT......Page 343 13.6.2 Modeling of IBM......Page 345 13.6.4 Stability (relaxation) of CTC layers with respect to time and temperature after IBM......Page 347 13.7.2 CTC with H2/CH4 plasmas......Page 349 13.8 Summary......Page 350 References......Page 351 14 Extrinsic Doping......Page 353 14.1 Introduction......Page 354 14.2 Impurity activity......Page 355 14.2.2 Group II impurities......Page 356 14.2.6 Group VI impurities......Page 357 14.3.1 CdTe......Page 358 14.3.2 LWIR and MWIR MCT......Page 359 14.4 Segregation properties of impurities......Page 360 14.4.1 Segregation in CdTe......Page 361 14.4.2 Segregation in LWIR and MWIR MCT......Page 362 14.5 Traps and recombination centers......Page 363 14.5.2 Reducing the concentrations of SRH centers......Page 364 14.6.1 In......Page 366 14.6.2 Iodine......Page 367 14.6.4 As......Page 368 14.7 Residual defects......Page 370 References......Page 371 15 Structure and Electrical Characteristics of Metal/MCT Interfaces......Page 375 15.1 Introduction......Page 376 15.2.2 In/MCT interface......Page 377 15.2.3 Ag/MCT interface......Page 378 15.2.6 Cr/MCT interface......Page 379 15.3.1 Al/MCT interface......Page 380 15.3.4 Ti/MCT interface......Page 381 15.3.6 Sn/MCT interface......Page 382 15.4.2 Device design and passivation requirements......Page 383 15.4.5 Passivation of MCT with CdTe......Page 384 15.5.2 Metal/MCT contacts......Page 390 15.5.3 Schottky barrier contacts......Page 391 15.6.1 Introduction......Page 392 15.6.3 Recombination velocity at heterointerfaces......Page 393 15.6.5 Gated photodiodes......Page 394 15.7.1 Introduction......Page 395 15.7.2 Surface structure and epitaxial growth......Page 396 15.7.3 RHEED analysis of the (211) surface......Page 397 15.7.4 Reconstruction of the (110) surface......Page 399 15.7.5 Reconstruction of the (100) surface......Page 401 15.7.6 Reconstruction of (111) surfaces......Page 403 References......Page 406 16 MCT Superlattices for VLWIR Detectors and Focal Plane Arrays......Page 411 16.1 Introduction......Page 412 16.2 Why HgTe-based superlattices......Page 413 16.2.1 Advantages of HgTe/CdTe superlattices over MCT alloys......Page 414 16.2.2 Problems with the use of HgTe/CdTe superlattices in VLWIR detectors and FPAs......Page 417 16.2.3 Use of HgTe/CdTe superlattices as buffer layers on CdZnTe before MCT growth......Page 418 16.2.5 HgTe/ZnTe superlattices......Page 419 16.3.1 Normal electronic band structure: band structures and optical absorptivities......Page 420 16.3.2 Inverted electronic band structure: band structure and optical absorptivity......Page 421 16.4 Growth......Page 422 16.4.1 Substrate orientation......Page 423 16.4.2 Doping......Page 424 16.5 Interdiffusion......Page 425 16.5.1 Effect of interdiffusion on the bandgap and optical absorption spectra......Page 426 16.5.2 Measuring interdiffusion by X-ray diffraction......Page 427 16.5.3 Measuring interdiffusion by STEM......Page 429 16.6 Conclusions......Page 431 References......Page 432 17 Dry Plasma Processing of Mercury Cadmium Telluride and Related II–VIs......Page 435 17.1 Introduction......Page 436 17.2 Effects of plasma gases on MCT......Page 437 17.3.1 Physics of plasmas......Page 439 17.3.2 Hydrogen variations......Page 441 17.3.3 Plasma parameters – effects on II–VI semiconductors......Page 444 17.3.4 Plasma parameter change ECR to ICP......Page 446 17.4.1 Surface chemical analysis......Page 447 17.4.3 Ex vacuo atomic force microscopy......Page 449 17.5.1 Etch lag and lateral photoresist etching – ion angular distribution (microloading, RIE lag)......Page 452 17.5.2 Macroloading......Page 454 17.6 Plasma processes in the production of II–VI materials......Page 456 17.6.1 Trench delineation......Page 457 17.6.4 Microlenses and antireflective structures......Page 458 17.7 Conclusions and future efforts......Page 460 References......Page 461 18.1 Introduction......Page 465 18.1.1 Historical perspective and early detectors......Page 466 18.1.3 MCT photoconductive arrays......Page 467 18.2 Applications and sensor design......Page 468 18.3 Photoconductive detectors in MCT and related alloys......Page 470 18.3.1 Introduction to the technology of photoconductor arrays......Page 471 18.3.2 Theoretical fundamentals for LW arrays......Page 472 18.3.4 Nonequilibrium effects in photoconductors......Page 475 18.4.1 Introduction to the SPRITE detector......Page 476 18.4.2 SPRITE operation and performance......Page 477 18.5 Conclusions on photoconductive MCT detectors......Page 480 References......Page 481 Part Three - Applications......Page 483 19 HgCdTe Photovoltaic Infrared Detectors......Page 485 19.3 Applications......Page 486 19.4.1 Ideal photovoltaic devices......Page 487 19.4.2 Nonideal behavior in MCT diodes......Page 488 19.5.1 Thermal diffusion currents in MCT......Page 490 19.5.3 Interband tunnelling......Page 491 19.5.5 Impact ionization......Page 492 19.6 Manufacturing technology for MCT arrays......Page 493 19.6.2 Via-hole technologies using LPE......Page 494 19.6.3 Planar device structures using LPE......Page 495 19.6.4 Double layer heterojunction devices (DLHJ)......Page 496 19.6.5 Wafer-scale processes using vapor phase epitaxy on low-cost substrates......Page 497 19.7.1 Two-color array technology......Page 499 19.7.2 Higher operating temperature (HOT) device structures......Page 500 References......Page 501 20.1 Introduction......Page 505 20.2.1 Introduction and theory......Page 506 20.2.2 Nonequilibrium detectors......Page 509 20.3.1 Introduction......Page 512 20.3.2 Mesa diodes......Page 513 20.3.3 Planar diodes......Page 518 20.3.4 Stacked loophole......Page 519 20.4 Emission devices......Page 520 References......Page 525 21.1 Introduction and applications......Page 529 21.2 The avalanche multiplication effect......Page 530 21.3 Physics of MCT EAPDs......Page 531 21.3.1 Phenomenological model for EAPDs......Page 532 21.3.2 Energy dispersion factor, α(E)......Page 533 21.3.3 Impact ionization threshold energy......Page 535 21.3.4 EAPD diodes at room temperature......Page 537 21.3.5 MCT EAPD dark currents......Page 539 21.4.1 Theoretical foundations for the EAPD device technology......Page 540 21.4.2 Via-hole technology......Page 541 21.5.1 Avalanche gain......Page 542 21.5.3 Dark current......Page 543 21.6 LGI as a practical example of MCT EAPDs......Page 546 References......Page 547 22.1 Introduction......Page 549 22.2.1 Generalized model......Page 550 22.2.2 Reduced volume devices......Page 553 22.2.3 Design of high temperature photodetectors......Page 554 22.3.1 Ultimate performance of HgCdTe devices......Page 555 22.3.2 Non-equilibrium devices......Page 557 22.4 Photoconductive devices......Page 558 22.5.1 PEM detectors......Page 560 22.5.2 Magnetoconcentration detectors......Page 561 22.6 Photodiodes......Page 562 22.6.2 Practical HgCdTe photodiodes......Page 563 References......Page 571 Index......Page 575