Journal of Electronic Material., Vol. 24, No.5, 1995 Special Issue Paper How Dislocations Affect Transport A.T. PAXTON Department of Materials, University of Oxford, OXl3PH, U.K A. SHER, M. BERDING, M. VAN SCHILFGAARDE SRI International, Menlo Park, CA 94025 M.W. MULLER Washington University, St. Louis, MO 63130 Dislocations crossing a junction in HgCdTe have little effect on detector responsivity, but are known to reduce the zero bias impedance RJ\. and increase the leakage current, especially at low temperatures where RoAis dominated by tunneling and generation/recombination processes. We have calculated the Coulomb and piezoelectric fields associated with dislocations in an attempt to interpret their effect on the junction's transport properties. Dislocation electric fields can affect transport since they are superimposed on the built-in and applied junction fields which control the currents. The screening ofthe fields in the neutral region is consistent with the dislocations' small effect on responsiv- ity. Their impact in the space charge region is found to be significant and consistent with the nonlinear dependence ofperformance on dislocation density. The piezoelectric potential of the typical 60° dislocation in a sphalerite crystal, and the Coulomb potential ofa dislocation crossing the junction plane other than normally, are angularly varying in the junction plane. Angular variation of the potentials can be qualitatively interpreted as an angular modulation of the potential barrier. Because of the nonlinear dependence ofjunction currents on the barrier (or the junction potential), the angular variation ofthe currents does not vanish upon averaging. We find that the range of the Coulomb potential is too small to account for a major portion of the experimentally reported perfor- mance degradation but may be responsible for the reduction ofRoAat cryogenic temperatures and low dislocation density, and that the longer range piezoelec- tric potential may be important. We also find that superposing the potentials of neighboring dislocations, because of the nonlinear dependence of junction leakage currents onjunction potentials may account for the observed nonlinearity of performance degradation with dislocation density as measured by etch pit density. Key words: Dislocations, HgCdTe, piezoelectric, transport properties (Received December 21, 1993; revised August 15, 1994) by liquid-phase epitaxy (LPE) on lattice-matched CdZnTe substrates. Typical values of active (n layer) and cap (p layer) compositionsare x =0.2241and x ~ 0.28, respectively. The n layers are typically indium- doped in the growth process, with carrier concen- trations as low as permitted by series resistance and capacitance concerns, but usually realized at > 2 x 1015 cm-3. The cap p+ layers are typically arsenic doped with p ==2X1017cm-3.Themetallurgical p-njunction INTRODUCTION The p-on-n Hg1_",Cd",Te(MCT) double layer heterojunction (DLHJ) mesa-diode-based focal plane arrays (FPAs) shown in Fig. 1 are currently leading the art in long-wave infrared (LWIR) applications. The most effective structures to date are those grown 525