Planar n-on-p HgCdTe FPAs for LWIR and VLWIR Applications

Abstract

Mainly driven by space applications, mercury cadmium telluride (MCT) focal-plane arrays (FPAs) have been successfully developed for very long wavelengths (k CO > 14 lm at 55 K). For this purpose, the standard n-on-p technology based on MCT grown by liquid-phase epitaxy (LPE) and involving vacancy doping has been modified to extrinsic doping by a monovalent acceptor. Due to the planar diode geometry obtained by ion implantation, most of the carrier generation volume is located in the p-type region with a thickness of approximately 8 lm. According to our understanding, the Shockley-Read centers connected with the Hg vacancies are thus significantly reduced. This situation should lead to longer minority-carrier lifetimes and smaller generation rates under equilibrium conditions, therefore yielding lower dark current. We indeed observe a reduction by a factor of approximately 15 by using extrinsic doping. Recent dark current data obtained in the temperature range from 55 K to 85 K on 288 9 384 FPAs with k CO (60 K) = 12 lm, either intrinsically or extrinsically doped, corroborate this finding. These data, new results on a 112 9 112 pixel demonstrator array with k CO (55 K) = 14.4 lm, and earlier measurements are compared with Tennant's Rule 07 established for p-on-n technology.

Infrared detectors for space applications

“…An optimized readout scheme is implemented to reach 4.8 kHz frame rate for the 128 × 128 subframe using 16 video outputs. Advanced VLWIR HgCdTe (MCT) material is used, based on extrinsically doped liquid-phase epitaxy (LPE) grown absorber layers for low-dark-current applications [10].…”

Below Rule’07 low dark current LWIR and VLWIR MCT 2D focal plane detector arrays from AIM

“…In recent years, high-operation temperature (HOT) detector applications in the mid-wave infrared spectral range (MWIR) have widely attracted attention [1,2]. In the LWIR and VLWIR spectral ranges, an increase in operating temperature while keeping the detector performance obtained at lower temperatures proved to be significantly more difficult.…”

Characterization and Simulation of p-Type Ion Implantation in MCT

“…In fact, the core element of MCT-based infrared detectors is typically a photodiode based on p-n junction structure, generating a photogenerated potential under the excitation of infrared photons. The p-n junction can be formed either on the p-type absorbing layer or on the n-type absorbing layer, corresponding to n-on-p device [2,3] and p-on-n device [4], respectively. In the traditional n-on-p device, the in-situ p-type doping can be achieved by Hg vacancy doping [5] and Au or Cu incorporation [6] during epitaxy growth; the n-type doping can be acquired by boron ion implantation.…”