chapter 9, Alternative Uncooled Long-Wavelength IR Photodetectors

Excerpt

As alternatives to the current market-dominant HgCdTe, a number of II–VI and III–V semiconductor systems have been proposed, including Hg_1−xZn_xTe (HgZnTe), Hg_1−xMn_xTe (HgMnTe), InAs_1−xSb_x (InAsSb), InSb_1−xBi_x (InSbBi), In_1−xTl_xSb (InTlSb), and InAs-GaSb type-II superlattices.

The wide body of information concerning different methods of crystal growth and physical properties is gathered in Chapter 3. This chapter concentrates on the technology and performance of IR detectors fabricated from Hg-based and III–V materials.

9.1 HgZnTe and HgMnTe Detectors

The technology for HgZnTe IR detectors has benefitted greatly from the HgCdTe device technology base. In comparison with HgCdTe, HgZnTe detectors are easier to prepare due to their relatively higher hardness. The development of device technology requires reproducible high-quality, electronically-stable interfaces with a low interface state density. It was found that the tendency to form surface inversion layers on HgZnTe by anodization is considerably lower than that of HgCdTe. Also, fixed charges at the anodic oxide-HgZnTe interface (2×10¹⁰cm⁻² at 90 K) are lower. Additionally, it has been observed that the anodic oxide-HgZnTe interface is more stable under thermal treatment than the anodic-HgCdTe interface.

The first HgZnTe photoconductive detectors were fabricated by Nowak in the early 1970s. Because of their early stage of development, the performance of these devices was inferior to that of HgCdTe. Then Piotrowski et al. demonstrated that p-type Hg_0.885Zn_0.115Te can be used as a material for high-quality ambient 10.6-μm photoconductors. These photoconductors, working at 300 K, can achieve 10⁸ cm Hz^1/2W⁻¹ detectivity with optimized composition, doping, and geometry. (Aspects of theoretical performance for both photoconductive and photovoltaic detectors are discussed in Refs. 1–3 and 20–23.)