V. S. Varavin

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.

The heteroepitaxy of II–VI compounds on the non-isovalent substrates (ZnTe/Si)

Abstract At a heteroepitaxy of non-isovalent compounds with tetrahedral coordination of bonds it is necessary, that the conditions of epitaxy provided an interface balance of valence electrons applicable to the tetrahedral configuration of bonds. The counting of the number of valence electrons was considered with Si–ZnTe interface formation. For preservation tetrahedral coordination the numbers of bonds of Zn and of Te with silicon should be equal. This condition will not hold for the most orientations of substrate surface. It is also necessary to allow for the presence of surfactants (As), which have a different valency from that of silicon. The arsenic on Si(013) and on Si(113) at temperatures up to 870 K formed adsorption layers close to single monolayers. Tellurium and zinc in contrast to arsenic, are adsorbed at temperatures of ZnTe nucleating and growth (570–670 K) in small numbers (

Acceptor states in heteroepitaxial CdHgTe films grown by molecular-beam epitaxy

The photoluminescence method is used to study acceptor states in CdHgTe heteroepitaxial films (HEFs) grown by molecular-beam epitaxy. A comparison of the photoluminescence spectra of HEFs grown on GaAs substrates (CdHgTe/GaAs) with the spectra of CdHgTe/Si HEFs demonstrates that acceptor states with energy depths of about 18 and 27 meV are specific to CdHgTe/GaAs HEFs. The possible nature of these states and its relation to the HEF synthesis conditions and, in particular, to the vacancy doping occurring under conditions of a mercury deficiency during the course of epitaxy and postgrowth processing are discussed.

Defects in heteroepitaxial CdHgTe/Si layers and their behavior under conditions of implanted p + - n photodiode structure formation

The impurity-defect structure of heteroepitaxial CdxHg1 − xTe/Si (0.35 < x < 0.39) layers grown by molecular beam epitaxy for the creation of arsenic-ion-implanted p+-n junctions has been studied by the photoluminescence method. It is established that full realization of the possibilities of p+-on-n photodiode structures based on the CdHgTe/Si system is hindered by uncontrolled doping of the material that leads to the formation of both shallow (impurity level energy ∼10 meV) and deep (∼50 meV) acceptor levels.

Determining surface recombination rates in epitaxial layers of n-CdxHg1−xTe from measurements of the planar magnetoresistance and relaxation times for nonequilibrium charge carriers

The dependence of the planar magnetoresistance on magnetic field has been measured for epitaxial layers of n-CdxHg1−x (x=0.211, 0.22) at 300 and 77 K. The 77 K measurements were made in electric fields below and above the threshold field for avalanche impact ionization. The measurement results for the planar magnetoresistance and relaxation time of nonequilibrium charge carriers are used to determine surface recombination rates.

Charge-carrier lifetime in Hg1−xCdxTe (x=0.22) structures grown by molecular-beam epitaxy

Measurements of the charge carrier lifetime in epitaxial structures based on narrow-gap Hg1−xCdxTe (x=0.22), grown by molecular-beam epitaxy with pulsed excitation using radiation at different wavelengths, are reported. It is shown that in p-type epitaxial films the lifetime is determined by the Auger recombination mechanism at temperatures corresponding to the impurity conductivity, and for n-type epitaxial films recombination via local centers is characteristic.

A study of galvanomagnetic phenomena in MBE-grown n-CdxHg1−xTe films

The magnetic-field dependences of the Hall coefficient and the conductivity of n-type CdxHg1−xTe epitaxial structures were measured at 77 K. The structures were grown by molecular-beam epitaxy with a prescribed solid solution composition profile across the thickness. A specific feature of the obtained dependences is that the conductivity and the absolute value of the Hall coefficient decrease with an increasing magnetic field. The obtained experimental dependences can only be described in terms of a model including low-mobility electrons. It is shown that anodic oxide deposited onto the CdxHg1−xTe film surface makes the concentration of low-mobility electrons higher and that of anodic fluoride lower. The possible reasons for the appearance of low-mobility electrons are discussed. The most probable sources of such electrons are surface layers and electrical microheterogeneities in CdxHg1−xTe films.

Defects in mercury-cadmium telluride heteroepitaxial structures grown by molecular-beam epitaxy on silicon substrates

Defects in mercury-cadmium-telluride heteroepitaxial structures (with 0.3 to 0.4 molar fraction of cadmium telluride) grown by molecular-beam epitaxy on silicon substrates are studied. The low-temperature photoluminescence method reveals that there are comparatively deep levels with energies of 50 to 60 meV and shallower levels with energies of 20 to 30 meV in the band gap. Analysis of the temperature dependence of the minority carrier lifetime demonstrates that this lifetime is controlled by energy levels with an energy of ∼30 meV. The possible relationship between energy states and crystal-structure defects is discussed.