Beam Epitaxy Growth Of HgCdTe Research Articles

Recent Progress in MBE Growth of CdTe and HgCdTe on (211)B GaAs Substrates

Alternate substrates for molecular beam epitaxy growth of HgCdTe including Si, Ge, and GaAs have been under development for more than a decade. MBE growth of HgCdTe on GaAs substrates was pioneered by Teledyne Imaging Sensors (TIS) in the 1980s. However, recent improvements in the layer crystal quality including improvements in both the CdTe buffer layer and the HgCdTe layer growth have resulted in GaAs emerging as a strong candidate for replacement of bulk CdZnTe substrates for certain infrared imaging applications. In this paper the current state of the art in CdTe and HgCdTe MBE growth on (211)B GaAs and (211) Si at TIS is reviewed. Recent improvements in the CdTe buffer layer quality (double crystal rocking curve full-width at half-maximum ≈ 30 arcsec) with HgCdTe dislocation densities of ≤106 cm−2 are discussed and comparisons are made with historical HgCdTe on bulk CdZnTe and alternate substrate data at TIS. Material properties including the HgCdTe majority carrier mobility and dislocation density are presented as a function of the CdTe buffer layer quality.

HgCdTe Research at FFI: Molecular Beam Epitaxy Growth and Characterization

This paper presents results from recent work on molecular beam epitaxy growth of HgCdTe at the Norwegian Defence Research Establishment (FFI), including studies of material properties and fabrication of photodiodes and nanostructures. Systematic studies of defect morphology in HgTe and Hg1� xCdxTe have revealed that there is a minimum in the area covered by defects just below the onset of Te precipitation. The shape and density of microvoids in HgTe can be used to determine the deviation from the optimal growth temperature. This can be further related to the optimal growth temperature of Hg1� xCdxTe with any Cd mole fraction by thermodynamic calculations. A mechanism for the formation of microvoids and needles has been presented. Photoluminescence (PL) has been used to study layers without doping and with Hg vacancy, Ag, and In doping. Planar photodiodes with high dynamic resistance and good quantum efficiency were fabricated by ion-milling vacancy-doped mid-wave and long-wave infrared layers. Quantum wells (QWs) with good crystallinity and high PL light output have been grown. Surface patterning has been found to enhance light emission from HgCdTe thin-film and QW samples by � 30%. Single-crystal HgTe and segmented HgTe/Te nanowires have been grown, and the resistivity of the nanowires has been measured by conductive atomic force microscopy (AFM), where the AFM tip has been used as a mobile electrode.

Real-time mass spectroscopy of reflected fluxes during molecular beam epitaxy growth of HgCdTe

The interaction between molecular beams present in the growth of HgCdTe was studied using reflection mass spectroscopy (REMS). The incident Hg flux was found to strongly influence the amount of Te and Cd reflected from the growth surface, and also, the incident Te flux influences the amount of Cd reflected from the surface. Based on these observations, it appears that the CdTe growth rate is influenced by the amount of excess Te and/or Hg available at the growth surface. A technique to control accurately the layer mole fraction by measuring the ratio of Cd to Cd+Te fluxes during growth has been investigated. The results of the postgrowth layer characterization by secondary ion mass spectroscopy and infrared transmission indicate a strong correlation between the REMS ratio and the mole fraction of the resulting layer. This technique has successfully been used to correct for long term and short term drifts in effusion cell output.

Molecular beam epitaxy growth of HgCdTe for high performance infrared photon detectors

Significant progresses have been made in the molecular beam epitaxy (MBE) growth of HgCdTe for high performance infrared photon detectors with the aid of in situ and ex situ characterization techniques. Superlattice interfacial layers compensate in part for the influence of non-ideal CdZnTe substrates and hence improved the material quality as well as yield. They result in photoconductive carrier recombination lifetimes approaching theoretical limits set by the intrinsic radiative and Auger recombination mechanisms for 8–14μm long-wavelength infrared HgCdTe. Very high composition and thickness uniformities have also been achieved. However, the Urbach tail energy, which is associated with structural disorder, was found to be non-uniform for both large wafer (up to 20×20mm2) and very small area (down to 200×200μm2). After several years of improvements in MBE HgCdTe growth techniques, substrates once again have become a bottleneck to further improvements.

Molecular beam epitaxy growth of HgCdTe on Ge for third-generation infrared detectors

The Leti-Lir has studied II–VI compounds for infrared (IR) detection for more than 20 years. The need to reduce the production cost of IR focal plane arrays (FPAs) sparked the development of heteroepitaxy on large-area substrates. Germanium has been chosen as the heterosubstrate for the third generation of IR detectors. First, we report on the progress achieved in HgCdTe growth on 3-in. and 4-in. (211)B CdTe/Ge. Then, we discuss the choice of a new machine for larger size and better homogeneity. Finally, we present the latest results on third-generation IR multicolor and megapixel devices. First-time results regarding a middle wavelength infrared (MWIR) dual-band FPA, with a reduced pitch of 25 µm, and a MWIR 1,280×1,024 FPA will be shown. Both detectors are based on molecular beam epitaxy (MBE)-grown HgCdTe on Ge. The results shown validate the choice of Ge as the substrate for third-generation detectors.