High-Performance LWIR MBE-Grown HgCdTe/Si Focal Plane Arrays

Abstract

We have been actively pursuing the development of long-wavelength infrared (LWIR) HgCdTe grown by molecular beam epitaxy (MBE) on large-area silicon substrates. The current effort is focused on extending HgCdTe/Si technology to longer wavelengths and lower temperatures. The use of Si versus bulk CdZnTe substrates is being pursued due to the inherent advantages of Si, which include available wafer sizes (as large as 300 mm), lower cost (both for the substrates and number of die per wafer), compatibility with semiconductor processing equipment, and the match of the coefficient of thermal expansion with silicon read-out integrated circuit (ROIC). Raytheon has already demonstrated low-defect, high-quality MBE-grown HgCdTe/Si as large as 150 mm in diameter. The focal plane arrays (FPAs) presented in this paper were grown on 100 mm diameter (211)Si substrates in a Riber Epineat system. The basic device structure is an MBE-grown p-on-n heterojunction device. Growth begins with a CdTe/ZnTe buffer layer followed by the HgCdTe active device layers; the entire growth process is performed in situ to maintain clean interfaces between the various layers. In this experiment the cutoff wavelengths were varied from 10.0 lm to 10.7 lm at 78 K. Detectors with >50% quantum efficiency and R 0 A~1000 Ohms cm 2 were obtained, with 256 · 256, 30 lm focal plane arrays from these detectors demonstrating response operabilities >99%.

Nature of Growth Pits in Lead Salt Epilayers Grown by Molecular Beam Epitaxy

“…Although more than an order of magnitude reduction of the growth pit density has been achieved by using our optimized growth condition, the density is still slightly higher than the macrodefect density of state-of-the-art HgCdTe epilayers grown by MBE on Si substrates. 14 Due to the limited resolution and depth of field associated with Nomarski optical microscopy, it is difficult to obtain clear images of the structures and morphologies of the growth pits. In this section, detailed information about the growth pits in PbSe epilayers will be presented based on SEM observation.…”

Flexibility of p–n Junction Formation from SWIR to LWIR Using MBE-Grown Hg(1–x)Cd x Te on Si Substrates

“…It has to be noted that As doping behaves well after the activation annealing of the layer grown is performed. The quality of the p-n junction is validated by the performances of detectors in the LWIR 12,23,24 and MWIR 3 ranges, as previously reported. Short-wave avalanche photodetector (APD) results were recently obtained and will be published elsewhere.…”

Infrared Detectors for the Future

“…By comparison, HgCdTe epitaxial layers grown by MBE or LPE on bulk CdZnTe have typical EPD values in the 10 4 to mid-10 5 cm −2 range where there is a negligible effect of dislocation density on detector performance. At 77 K, diode performance with cut-off wavelength in LWIR region for HgCdTe on Si is comparable to that on bulk CdZnTe substrates [25].…”