I. V. Sabinina

Molecular-beam epitaxy of mercury-cadmium-telluride solid solutions on alternative substrates

Growth processes were considered for heteroepitaxial structures based on a mercury-cadmium-telluride (MCT) solid solution deposited on GaAs and Si alternative substrates by molecular-beam epitaxy. Physical and chemical processes of growth and defect-generation mechanisms were studied for CdZnTe epitaxy on atomically clean singular and vicinal surfaces of gallium-arsenide substrates and CdHgTe films on CdZnTe/GaAs surfaces. ZnTe single-crystalline films were grown on silicon substrates. Methods for reducing the content of defects in CdZnTe/GaAs and CdHgTe films were developed. Equipment for molecular-beam epitaxy was designed for growing the heteroepitaxial structures on large-diameter substrates with a highly uniform composition over the area and their control in situ. Heteroepitaxial MCT layers with excellent electrical parameters were grown on GaAs by molecular-beam epitaxy.

Defect formation during growth of CdTe(111) and HgCdTe films by molecular beam epitaxy

(111)B CdTe films and (111)B and (112)B HgCdTe films were grown by MBE. The films were examined by optical and transmission electron microscopy. Formation of the microtwins and dislocations was observed in the films. The HgCdTe films contained some complicated defects also. The interaction of partial dislocations in the twinning plane results in the creation of threading dislocations. The increase of twin boundary density leads to an increase of the threading dislocation density in CdTe (111)B films. The existence of the elemental tellurium phase is possible during Hg0.8Cd0.2Te film growth by MBE. This circumstance in combination with the twinning process leads to the avalanche-type multiplication of the structure defects.

Defect structure of HgCdTe films grown by molecular beam epitaxy on Si substrates

An ion milling-assisted study of defect structure of HgCdTe films grown by molecular beam epitaxy on Si substrates was performed. The films appeared to contain initially neutral Te-related defects with concentration of 1017 cm−3, typical of HgCdTe. The concentration of residual donors was found to be quite low ((3–8) × 1014 cm−3). Specific to HgCdTe/Si technology appeared to be a considerable number of stacking faults, which affected the carrier mobility in n-type material. These defects can be annealed in He atmosphere at 230 °C, and after ion milling the electrical parameters of n-type HgCdTe/Si films approach those of high-quality bulk crystals.

HgCdTe Heterostructures on Si (310) Substrates for Midinfrared Focal Plane Arrays

Results of studies of the molecular beam epitaxial growth of HgCdTe alloys on Si substrates as large as 100 mm in diameter are presented. Optimum conditions for obtaining HgCdTe/Si(310) heterostructures of the device quality for the spectral range of 3–5 μm are determined. The results of measurements and discussion of photoelectric parameters of an infrared photodetector of a format of 320 × 256 elements with a step of 30 μm based on a hybrid assembly of a matrix photosensitive cell with a Si multiplexer are presented. A high stability of photodetector parameters to thermocycling from room temperature to liquid-nitrogen temperature is shown.

Defects in the crystal structure of CdxHg1 − xTe layers grown on the Si (310) substrates

Microstructure of the CdTe (310) and CdHgTe (310) layers grown by molecular-beam epitaxy on Si substrates has been studied by the methods of transmission electron microscopy and selective etching. It is established that formation of antiphase domains in the CdHgTe/CdTe/ZnTe/Si(310) is determined by the conditions of formation of the ZnTe/Si interface. Monodomain layers can be obtained by providing conditions that enhance zinc adsorption. An increase in the growth temperature and in the pressure of Te2 vapors gives rise to antiphase domains and induces an increase in their density to the extent of the growth of poly-crystals. It is found that stacking faults exist in a CdHgTe/Si(310) heterostructure; these defects are anisotropically distributed in the bulk of grown layers. The stacking faults are predominantly located in one (111) plane, which intersects the (310) surface at an angle of 68°. The stacking faults originate at the ZnTe/Si(310) interface. The causes of origination of stacking faults and of their anisotropic distribution are discussed.

Effect of low-temperature annealing on electrical properties of n-HgCdTe

The effect of low-temperature isothermal annealing on electrical properties of CdxHg1−xTe (mercury cadmium telluride, MCT) films is investigated. Films of n-type conduction with x=0.21–0.23 were grown on GaAs substrates by MBE. Annealings of 1–1000 h duration were carried out at 90–230°C. The changes in conductivity, the Hall factor, and the lifetime of minority carriers after annealing are explained by the formation of mercury vacancies and egress of Hg atoms from the sample. The effect of various surface coatings on the rate of variation of MCT film electrical properties was investigated. An anodic oxide appeared to be the most efficient coating to stabilize the parameters of n-type films. The analysis of the magnetic-field dependences of the Hall factor and conductivity has shown that the observed modification of parameters upon annealing can be described in terms of a two-layer model with two types of electrons—high and low mobility.

320×256 HgCdTe IR FPA with a built-in shortwave cut-off filter

A photovoltaic detector design based on the graded band gap HgCdTe MBE structure with high conductivity layer (HCL) at interface, which provides photodiodes series resistance and a shortwave cut.off filter is developed. The optimal HCL parameters giving high quantum efficiency and minimal noise equivalent temperature difference were determined by calculations and experimentally confirmed. The hybrid 320×256 IR FPA operating in 8–12 μm spectral range was fabricated. The threshold power responsivity and minimal noise equivalent temperature difference values at wavelength maximum were 1.02×10−7 W/cm2, 4.1×108 V/W and 27 mK, respectively.

Density of dislocations in CdHgTe heteroepitaxial structures on GaAs(013) and Si(013) substrates

Epitaxial layers of CdxHg1–xTe (MCT) on GaAs(013) and Si(013) substrates were grown by molecular beam epitaxy. The introduction of ZnTe and CdTe intermediate layers into the structures made it possible to retain the orientation close to that of the substrate in MCT epitaxial layers despite the large mismatch between the lattice parameters. The structures were investigated using X-ray diffraction and transmission electron microscopy. The dislocation families predominantly removing the mismatch between the lattice parameters were found. Transmission electron microscopy revealed Γ-shaped misfit dislocations (MDs), which facilitated the annihilation of threading dislocations. The angles of rotation of the lattice due to the formation of networks of misfit dislocations were measured. It was shown that the density of threading dislocations in the active region of photodiodes is primarily determined by the network of misfit dislocations formed in the MCT/CdTe heterojunction. A decrease in the density of threading dislocations in the MCT film was achieved by cyclic annealing under conditions of the maximally facilitated nonconservative motion of dislocations. The dislocation density was determined from the etch pits.

High-performance 320 × 256 long-wavelength infrared photodetector arrays based on CdHgTe layers grown by molecular beam epitaxy

This paper gives the parameters of 320 × 256 element long-wavelength infrared photodetectors fabricated by a new improved technology based on heteroepitaxial mercury-cadmium-tellur structures. In these photodetectors, the variation of the photodiode bias voltage over the area of the array is minimized; inefficient photodiode regions related to both hybridization and spike-shaped growth defects of epitaxial films are eliminated; the current-voltage characteristics of the diodes in the resulting photodetectors are homogeneous and are limited by the diffusion current component up to −400 mV. The dark current is 0.25–0.45 nA, and R0A = (0.6–3) · 102 Ω · cm2. The voltage sensitivity, the threshold irradiance, and the average NETD at the maximum sensitivity are 11.8 · 108 V/W, 3.7 · 10−8 W/cm2, and 26.8 mK, respectively. The percentage of defective elements is 1.5%.

Mercury cadmium telluride surface passivation by the thin alumina film atomic-layer deposition

We analyzed the C-V curves of CdхHg1-хTe-based (x ∼ 0.22) MIS structures with Al2O3 as an insulator. Alumina films were deposited on p and n type CdхHg1-хTe by atomic layer deposition. C-V curve specific features at high and low frequencies were found to be a result of the semiconductor-dielectric interface surface state influence. The surface state density was derived from the fitting experimental C-V curves at high and low frequencies with the theoretical model. The calculated curves were obtained by solving Poisson and continuity equations within the drift-diffusion model. The charge exchange between the surface states and permitted bands was supposed to be conducted using the Shockley-Read-Hall mechanism.