K. D. Mynbaev

Modification of Hg1−xCdxTe properties by low-energy ions

We present an overview concerning the modification of properties of HgCdTe solid solutions and related Hg-containing materials under surface treatment with low-energy (60–2000 eV) ion beams. The conditions for conductivity-type conversion in p-material, dose, and time dependences of the depth of the conversion layer are analyzed. The modification of electrical properties of n-type material subjected to ion-beam treatment is discussed. The suggested mechanisms of conductivity-type conversion under low-energy ion treatment of HgCdTe doped with vacancies or acceptor impurities are regarded. Properties of p-n junctions produced by this technique are reviewed, and electrical and photoelectric parameters of HgCdTe IR photodetectors fabricated by low-energy ion treatment are analyzed. Several examples of novel device structures developed with the use of the method are presented.

Doping of epitaxial layers and heterostructures based on HgCdTe

Available publications concerned with doping of epitaxial layers of HgCdTe alloys and heterostructures based on these alloys are reviewed. The main changes in technology of HgCdTe doping, which occurred when device structures fabricated on the basis of bulk material were replaced by those based on epitaxial layers are analyzed. The specific features of the doping of HgCdTe epitaxial layers in the course of the growth of these layers by the liquid-phase epitaxy, metal-organic chemical vapor deposition, and molecular-beam epitaxy are considered. The electrical properties of the doped material are analyzed. The current concepts of the intrinsic defects in HgCdTe and the effect of these defects on the properties of HgCdTe are briefly considered.

Defect study in molecular beam epitaxy-grown HgCdTe films with activated and unactivated arsenic

A defect study was performed on molecular beam epitaxy-grown HgCdTe films in situ doped with arsenic. Doping was performed from either effusion cell or cracker cell, and studied were both as-grown samples and samples subjected to arsenic activation annealing. Electrical properties of the films were investigated with the use of ion milling as a means of “stirring” defects in the material. As a result of the study, it was confirmed that the most efficient incorporation of electrically active arsenic occurs at the cracking zone temperature of 700u2009°C. Interaction between arsenic and tellurium during the growth was observed and is discussed in the paper.

Conductivity type conversion in ion-milled p-HgCdTe:As heterostructures grown by molecular beam epitaxy

Conductivity type conversion in ion-milled As-doped p-HgCdTe heterostructures grown by molecular beam epitaxy on GaAs substrates has been studied. It was found that in these heterostructures, donor center concentration (∼1017cm−3) after ion milling was much higher than that could have been expected as a result of interaction of interstitial mercury atoms, generated under the milling, with the As acceptors. One possible reason of the donor center formation is the activation of an intrinsic neutral defect, which was present in the HgCdTe:As prior to the ion milling. The nature of the donor centers formed is discussed.

Temperature dependence of the threshold current of QW lasers

The temperature dependence of the threshold current in GaInAs-based laser structures has been studied in a wide temperature range (4.2 ≤ T ≤ 290 K). It is shown that this dependence is monotonic in the entire temperature interval studied. Theoretical expressions for the threshold carrier density are derived and it is demonstrated that this density depends on temperature linearly. It is shown that the main contribution to the threshold current comes from monomolecular (Shockley-Read) recombination at low temperatures. At T > 77 K, the threshold current is determined by radiative recombination. At higher temperatures, close to room temperature, Auger recombination also makes a contribution. The threshold current grows with temperature linearly in the case of radiative recombination and in accordance with T3 in the case of Auger recombination.

Conduction type conversion in ion etching of Au- and Ag-doped narrow-gap HgCdTe single crystal

Fundamental aspects of the p-to-n conductivity type conversion induced by ion etching in HgCdTe single crystals diffusion-doped with Au and Ag have been studied. A conversion mechanism is suggested, according to which interstitial mercury atoms rapidly diffuse from the surface source with high concentration and “kick out” impurity atoms from the cation sublattice into interstitial positions and thereby convert impurity atoms from the acceptor state to the donor state. It is shown that the structure of defects in the converted layer is unstable and the electrical parameters of this layer vary when stored at room temperature. The most probable mechanism of this process at room temperature is decomposition of an oversaturated solution of the impurity. A re-conversion to the p-type, observed in isochronous annealing of samples, is due to impurity diffusion into the converted layer from the unconverted bulk of the sample or from microscopic impurity inclusions.

The nature of the compositional dependence of p?n junction depth in ion-milled p-HgCdTe

The dependence of conductivity-type conversion depth in vacancy-doped Hg1−xCdxTe (MCT) alloys subjected to ion milling on alloy composition and treatment temperature is studied both experimentally and theoretically. It is shown that both in compositionally homogeneous crystals and in samples with a wide bandgap protective layer the dependence is defined by internal electric fields, which affect the diffusion of mercury interstitial atoms that are generated during the treatment. Results of the calculation of the effect of the potentials of a p–n junction formed by ion milling and of a varyband structure field (in samples with the protective layer) on the conversion depth fit both the original experimental data and those taken from the literature well. The data obtained confirms the validity of the diffusion model of the formation of the excessive mercury source in MCT subjected to ion milling, which was proposed by the authors previously. The results presented in the paper allow one to predict and control the conversion depth in MCT subjected to ion milling for p–n junction fabrication, which makes them useful in MCT infrared detector technology.

Ion milling-assisted study of defect structure of HgCdTe films grown by liquid phase epitaxy

Ion milling, as a tool for “stirring” defects in HgCdTe by injecting high concentration of interstitial mercury atoms, was used for studying films grown by liquid phase epitaxy (LPE) on CdZnTe substrates. The films appeared to have very low residual donor concentration (∼1014 cm−3), yet, similar to the material grown by molecular beam epitaxy, contained Te-related neutral defects, which the milling activated electrically. It is shown that ion milling has a stronger effect on HgCdTe defect structure than thermal treatment, and yet eventually brings the material to an “equilibrium” state with defect concentration lower than that after low-temperature annealing.

Semi-insulating silicon carbide layers obtained by diffusion of vanadium into porous 4H-SiC

Semi-insulating silicon carbide layers have been obtained by diffusion of vanadium into porous 4H-SiC. The diffusion was performed from a film deposited by cosputtering of silicon and vanadium, with the content of the latter equal to 20%. The diffusion profile of vanadium in porous silicon carbide has a complex structure with a fast diffusion coefficient of 7×10−15 cm2/s. The activation energy of the resistivity of vanadium-diffusion-doped porous SiC layers is 1.45 eV. The resistivity of vanadium-doped semi-insulating layers is 5×1011 Ω cm at 500 K, which exceeds the resistivity of undoped porous SiC by two orders of magnitude. The results obtained indicate that porous SiC is a promising material for semi-insulating substrates in device structures based on wide-bandgap semiconductors.

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.