Effect of Dislocations on VLWIR HgCdTe Photodiodes

Abstract

The effects of dislocations on very-long-wavelength infrared (VLWIR) HgCdTe photodiodes (cutoff wavelength >14 lm at 40 K) have been determined experimentally and analyzed. The photodiodes are in the back-illuminated configuration, fabricated from HgCdTe p-on-n double-layer heterostructure (DLHJ) films grown at BAE Systems by liquid phase epitaxy (LPE) onto lattice-matched (111) CdZnTe substrates. Arrays were hybridized to silicon ROICs to form focal plane arrays (FPAs). After characterization for dark current and response, the arrays were dehybridized and stripped of their metals and passivation layers. Dislocations were revealed using a Hä hnert and Schenk (H&S) etch. Pixel traceability was maintained throughout the analysis, permitting one-to-one correlation between photodiode performance and dislocation density measured within that photodiode. We found that response and dark current were correlated to etch pit density (EPD), which we assumed to be equal to dislocation density. Our results support earlier dislocation studies on larger-bandgap HgCdTe, which showed response was only weakly impacted by EPD, while dark current was strongly affected by EPD. Measured EPD values ranged from low 10 5 to low 10 7 cm -2 . Potential causes for this range in EPD are discussed.

Effect of Cycle Annealing Parameters on Dislocation Density Reduction for HgCdTe on Si

“…[1][2][3] However, their use in long-wavelength focal-plane arrays is limited by large dislocation densities, which are two orders of magnitude greater than for HgCdTe grown on lattice-matched CdZnTe substrates. 4,5 The increased dislocation density leads to higher dark currents in devices and poor performance in focal-plane arrays.…”

Dislocation Reduction of HgCdTe/Si Through Ex Situ Annealing

“…[1][2][3][4][5][6][7][8] However, the goal of advancing this material technology to the long-wavelength (LWIR) regime has been hampered by the one to two orders of magnitude increase in dislocation density with respect to HgCdTe grown on lattice-matched bulk CdZnTe substrates. This deficiency in dislocation density has been shown to limit lifetimes, 9,10 lower mobility of carriers, 11 lead to larger dark currents in longwavelength detectors, 12,13 and ultimately reduce focal-plane array operability. 9,14 Current growth methods of HgCdTe/Si result in a dislocation density of mid 10 6 cm À2 to low 10 7 cm À2 .…”

Molecular Dynamics Simulation of MBE Growth of CdTe/ZnTe/Si

“…22 These defects play a significant role in limiting HgCdTe device performance, especially in the long wavelength infrared (LWIR) and very long wavelength infrared (VLWIR) regimes. [23][24][25][26][27] Significant efforts have been mounted by many research and development groups to reduce the dislocation density in the CdTe epilayers, yet it remains in the low 10 5 cm À2 at best. 28 The use of an As monolayer on the Si substrate and a ZnTe buffer layer before the CdTe growth has resulted in some improvements.…”