Fabrication and Characterization of Small Unit-Cell Molecular Beam Epitaxy Grown HgCdTe-on-Si Mid-Wavelength Infrared Detectors

Abstract

Small 15 lm unit-cell mid-wavelength infrared (MWIR) detectors have been fabricated and characterized at Raytheon Vision Systems (RVS) to enable the development of high resolution, large format, infrared imaging systems. The detectors are fabricated using molecular beam epitaxy (MBE) grown 4-in. HgCdTe-on-Si wafers with a p-on-n double layer heterojunction (DLHJ) device architecture. Advanced fabrication processes, such as inductively coupled plasma (ICP) etching, developed for large format MBE-on-Si wafers and 20 lm unit-cell two-color triple layer heterojunction (TLHJ) focal plane arrays (FPAs) have been successfully extended and applied to yield high performance 15 lm unit-cell single color detectors that compare favorably with state-of-theart detectors with larger pitch. The measured 78 K MWIR cut-off wavelength for the fabricated detectors is near 5.5 lm, and the current-voltage characteristics of these devices exhibit strong reverse breakdown and RoA performance as a function of temperature with diffusion limited performance extending to temperatures down to 120 K.

Third-generation infrared photodetector arrays

“…29 Recently, the first large-format MWIR FPAs with pixel dimension of 15 m have been demonstrated. 30,31 It will be an extreme challenge to deploy a two-or three-color detector structure into a small pixel such as 18ϫ 18 m 2 . Current two-color simultaneous mode pixels with two indium bumps per pixel have not been built with pixels smaller than 25 m on a side.…”

Recent progress in third generation infrared detectors

“…The band gap of the SL is determined by the energy difference between the electron miniband and the first heavy hole state at the Brillouin zone center. As is described in [8], the InAs/Ga 1Àx In x Sb SLSs material system can have some advantages over bulk HgCdTe.…”

“…Recently, the first large format MWIR FPAs with pixel dimension of 15 mm have been demonstrated [7,8]. It will be an extreme challenge to deploy a two-or three-color detector structure into a small pixel such as 18 Â 18 mm 2 .…”

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.…”