LWIR HgCdTe on Si detector performance and analysis

Abstract

We have fabricated a series of 256 pixel 3 256 pixel, 40 mm pitch LWIR focal plane arrays (FPAs) with HgCdTe grown on (211) silicon substrates using MBE grown CdTe and CdSeTe buffer layers. The detector arrays were fabricated using Rockwell Scientific's double layer planar heterostructure (DLPH) diode architecture. The 78 K detector and focal plane array (FPA) performance are discussed in terms of quantum efficiency (QE), diode dark current and dark current operability. The FPA dark current and the tail in the FPA dark current operability histograms are discussed in terms of the HgCdTe epitaxial layer defect density and the dislocation density of the individual diode junctions. Individual diode zero bias impedance and reverse bias current-voltage (I-V) characteristics vs. temperature are discussed in terms of the dislocation density of the epitaxial layer, and the misfit stress in the epitaxial multilayer structure, and the thermal expansion mismatch in the composite substrate. The fundamental FPA performance limitations and possible FPA performance improvements are discussed in terms of basic device physics and material properties.

Relevance of Thermal Mismatch in Large-Area Composite Substrates for HgCdTe Heteroepitaxy

“…Most reports have blamed the large lattice mismatch associated with structural defects, which may reduce device performance. [11][12][13] On the other hand, materials issues including thermal expansion mismatch, could also have an impact on dislocation densities or other important defects in CdTe/Si composite substrates. However, little work has been performed to directly examine the impact of thermal mismatch effects in this epitaxial system.…”

Fast Detection of Precipitates and Oxides on CdZnTe Surfaces by Spectroscopic Ellipsometry

“…The surface film left over by the bromine (Br) and methanol (MeOH) etch was evaporated in situ at 250°C, as is routinely done [5][6][7] prior to HgCdTe growth. The evaporation is confirmed by the changes in the reflection high-energy diffraction and ellipsometric spectra.…”

“…5 However, neither of these solutions yields the anticipated results in the long-wavelength detection range (from 8 to 12 lm), for which bulk, latticematched cadmium-zinc telluride (Cd 1-y Zn y Te) is still indispensable. 6 The preparation of this substrate material and its subsequent characterization are vital to ensure the quality of the epitaxial layers and for a variety of device fabrication steps. [6][7] The most important characteristics that one would like to extract in a nondestructive manner are the surface stoichiometry, the presence of oxides and roughness.…”

“…6 The preparation of this substrate material and its subsequent characterization are vital to ensure the quality of the epitaxial layers and for a variety of device fabrication steps. [6][7] The most important characteristics that one would like to extract in a nondestructive manner are the surface stoichiometry, the presence of oxides and roughness. In order to do so, it is essential to possess a fundamental understanding of the Cd 0.96 Zn 0.04 Te surface chemistry, in particular that of the semiconductor-oxide interface.…”

Characterization of Smooth CdTe(111) Films by the Conventional Close-Spaced Sublimation Technique

“…10 The highest quality epitaxial HgCdTe films have been grown on bulk grown CdZnTe substrates with dislocation densities between 10 4 /cm 2 and mid-10 5 /cm 2 . [10][11][12][13][14] The problem with bulk grown CdZnTe substrates is that properties are not uniform across the surface (composition and lattice constant) and they are not available in large sizes. 10,14 In addition, CdZnTe has a large difference in thermal expansion coefficient with flip-chip bonded complementary metal-oxide semiconductor (CMOS) readout circuits.…”