256×256 focal plane array midwavelength infrared camera based on InAs/GaSb short-period superlattices

Abstract

An infrared camera based on a 256 ϫ 256 focal plane array (FPA) for the second atmospheric window (3-5 µm) has been realized for the first time with InAs/GaSb short period superlattices (SLs). The SL detector structure with a broken gap type-II band alignment was grown by molecular beam epitaxy on GaSb substrates. Effective bandgap and strain in the superlattice were adjusted by varying the thickness of the InAs and GaSb layers and the controlled formation of InSb-like bonds at the interfaces. The FPAs were processed in a full wafer process using optical lithography, chemical-assisted ion beam etching, and conventional metallization technology. The FPAs were flip-chip bonded using indium solder bumps with a read-out integrated circuit and mounted into an integrated detector cooler assembly. The FPAs with a cutoff wavelength of 5.4 µm exhibit quantum efficiencies of 30% and detectivity values exceeding 10 13 Jones at T ϭ 77 K. A noise equivalent temperature difference (NETD) of 11.1 mK was measured for an integration time of 5 ms using f/2 optics. The NETD scales inversely proportional to the square root of the integration time between 5 ms and 1 ms, revealing background limited performance. Excellent thermal images with low NETD values and a very good modulation transfer function demonstrate the high potential of this material system for the fabrication of future thermal imaging systems.

MBE grown type-II MWIR and LWIR superlattice photodiodes

“…For example, Fuchs and co-workers from the Fraunhofer Institute have demonstrated type-II InAs/GaInSb photodiodes having cutoff wavelengths ranging from 7.5 to 12 lm with performance characteristics similar to those obtained from HgCdTe-based diodes and argued that improvements in material and device quality would significantly enhance device performance [5]. Recent works have demonstrated high-performance superlattice based imaging arrays [8] and high temperature operation [9] in the 3-5 lm region as well as performance rivaling MCT in the 7-12 lm region [10].…”

InAs/GaSb type‐II superlattices for single‐ and dual‐color focal plane arrays for the mid‐infrared spectral range

“…Finally, the detector hybrid is anti-reflection coated and mounted into a stand-alone camera system with a 1 W linear Stirling cooler. Figure 2a shows the excellent image quality delivered from the first InAs/GaSb SL mid-IR camera realized with this technology in 2004 [4]. The fine structure of the clothing proves the very good MTF and the low cross talk between neighboring detector elements in the FPA.…”

Comparative Study of HgCdTe Etchants: An Electrical Characterization

“…With proper theoretical designs different types of emitters and detectors have been studied and many of them have been fabricated. [1][2][3][4][5] During the last few years, there has been tremendous research effort devoted to various aspects of surface treatments, which results in evolution of new surface treatments along the years. 6,7 While sophisticated focal plane arrays of sizes as large as 1,024 · 1,024 and more are now well under the manufacturing phase, there remain many unanswered questions about the nature of HgCdTe surface, answers to which would improve the performance, yield and stability of the focal plane arrays.…”