M. N. Drozdov

Segregation of indium in InGaAs/GaAs quantum wells grown by vapor-phase epitaxy

Distribution of indium atoms in structures which contained double InGaAs/GaAs quantum wells and were grown by vapor-phase epitaxy from metal-organic compounds was studied. Experimental indium-concentration profiles were obtained using Auger electron spectroscopy. A model of growth with allowance made for indium segregation and a model for the Auger profiling were used in the calculations of profiles. Fitting calculated profiles to experimental ones made it possible to estimate the activation energies for In-Ga exchange in the context of a kinetic model for segregation. These energies are found to be somewhat higher than those that are well known for molecular-beam epitaxy, which is related to stabilization of the growth surface by hydrogen atoms in a vapor-phase reactor.

Single-crystalline GaAs, AlGaAs, and InGaAs layers grown by metalorganic VPE on porous GaAs substrates

Conditions for the growth of single-crystalline GaAs, AlGaAs, and InGaAs layers by metalorganic VPE were established and the corresponding semiconductor films were obtained on porous GaAs substrates. Comparative data on the morphology, structure, and electrical homogeneity of the epitaxial layers grown on the porous and monolithic substrates are presented. It was found that passage to the porous substrates leads to changes in the film growth rate and morphology, the concentration of electrically active defects, and their distribution in depth of the epitaxial structures.

Room-temperature photoconductivity in the 1–2.6 µm range in InAs/GaAs heterostructures with quantum dots

We have studied the room-temperature photoconductivity in the wavelength range 1–2.6 μm in InAs/GaAs heterostructures with quantum dots (QDs). Specific features of these heterostructures grown using the metalorganic vapor phase epitaxy (MOVPE) were an increase in the amount of InAs during the formation of a sheet of QDs and the use of alternating low-and-high-temperature regimes during their overgrowth with a GaAs barrier layer. For the first time, the MOVPE-grown multilayer InAs/GaAs heterostructures with quantum dots exhibited photoluminescence in a wavelength range of up to 1.6 μm and the photoconductivity up to 2.6 μm at room temperature. The heterostructures exhibited a room-temperature voltage sensitivity of 3 × 103 V/W (within a Si-plate filter bandwidth) and a specific detectivity of 9 × 108 cm Hz1/2 W−1.

Optically active layers of silicon doped with erbium during sublimation molecular-beam epitaxy

A study is made of the electrical, optical, and structural properties of Si:Er layers produced by sublimation molecular-beam epitaxy. The Er and O contents in the layers, grown at 400–600°C, were as high as 5×1018 and 4×1019 cm−3, respectively. The electron concentration at 300 K was ∼10% of the total erbium concentration and the electron mobility was as high as 550 cm2/(V·s). Intense photoluminescence at 1.537 µm was observed from all the structures up to 100–140 K. The structure of the optically active centers associated with Er depended on the conditions under which the layers were grown.

The sandwich InGaAs/GaAs quantum dot structure for IR photoelectric detectors

A new possibility for growing InAs/GaAs quantum dot heterostructures for infrared photoelectric detectors by metal-organic vapor-phase epitaxy is discussed. The specific features of the technological process are the prolonged time of growth of quantum dots and the alternation of the low-and high-temperature modes of overgrowing the quantum dots with GaAs barrier layers. During overgrowth, large-sized quantum dots are partially dissolved, and the secondary InGaAs quantum well is formed of the material of the dissolved large islands. In this case, a sandwich structure is formed. In this structure, quantum dots are arranged between two thin layers with an increased content of indium, namely, between the wetting InAs layer and the secondary InGaAs layer. The height of the quantum dots depends on the thickness of the GaAs layer grown at a comparatively low temperature. The structures exhibit intraband photoconductivity at a wavelength around 4.5 μm at temperatures up to 200 K. At 90 K, the photosensitivity is 0.5 A/W, and the detectivity is 3 × 109 cm Hz1/2W−1.

Subnanometer Resolution in Depth Profiling Using Glancing Auger Electrons

A new method for Auger depth profiling, employing a difference in the escape depth of the Auger electrons emitted at nearly normal and glancing angles, is proposed and verified. The depth profiles obtained under optimum ion sputtering conditions with registration of the glancing Auger electrons exhibit a subnanometer (0.8 nm) depth resolution. This technique was successfully applied to the study of high-quality InxGa1−xAs/GaAs heterostructures with quantum wells grown by the method of metalorganic chemical vapor deposition.

Investigation of the compositional changes of a Y-Ba-Cu-O HTSC target under ion sputtering

An Auger electron spectroscopy study is reported of the elemental depth profile of Y-Ba-Cu-O HTSC targets subjected to ion-plasma sputtering in a magnetron deposition system and ion-beam sputtering in the Auger spectrometer chamber. It has been established that the process consists in all cases of predominant copper sputtering accompanied by the formation of a modified surface layer and of a copper-depleted region. This region is assumed to originate from intense copper diffusion from the bulk to the modified surface layer driven by a concentration gradient.

Growth of light-emitting SiGe heterostructures on strained silicon-on-insulator substrates with a thin oxide layer

The possibility of using substrates based on “strained silicon on insulator” structures with a thin (25 nm) buried oxide layer for the growth of light-emitting SiGe structures is studied. It is shown that, in contrast to “strained silicon on insulator” substrates with a thick (hundreds of nanometers) oxide layer, the temperature stability of substrates with a thin oxide is much lower. Methods for the chemical and thermal cleaning of the surface of such substrates, which make it possible to both retain the elastic stresses in the thin Si layer on the oxide and provide cleaning of the surface from contaminating impurities, are perfecte. It is demonstrated that it is possible to use the method of molecular-beam epitaxy to grow light-emitting SiGe structures of high crystalline quality on such substrates.

MOCVD-grown heterostructures with GaAs/AlGaAs Superlattices: Growth features and optical and transport characteristics

The results of studies of MOCVD growth regularities of GaAs/AlGaAs superlattices with narrow forbidden minibands are presented. The spectra of photoluminescence and X-ray diffraction are measured, the concentration distribution profiles of components are determined by secondary-ion mass spectrometry, and the concentration distribution of charge carriers are determined by the method of capacitance profiling. The relation of the growth modes of heterostructures to their crystalline characteristics and luminescent and electrical properties are studied. The photoluminescence measurements indicate the high quality of the superlattices. X-ray diffraction and the data on secondary ions confirm the high periodicity of the superlattices grown in the optimized modes. The nonlinear current-voltage characteristics with a region of negative differential conductivity at moderate voltages and subsequent current increase at higher voltages because of tunneling between the minibands is found for the superlattices grown in the optimal growth modes. Current oscillations at frequencies of ∼60 MHz were observed in the region of negative differential conductivity. The negative differential conductivity and oscillations confirm the presence of the electron localization effect in moderate electric fields in the first conductivity miniband, which emerges due to the Bragg reflection of carriers in the superlattice.

Photoluminescence up to 1.6 μm of quantum dots with an increased effective thickness of the InAs layer

Multilayered InAs/GaAs quantum dot (QD) heterostructures are produced by metal-organic gas phase epitaxy. The structures exhibit photoluminescence around 1.55 μm at 300 K. The specific feature of the technology is the growth of an InAs layer with an increased effective thickness deff to form QDs, in combination with low-temperature overgrowth of the QDs with a thin (6-nm) GaAs layer and with the annelaing of defects. By X-ray diffraction analysis and PL studies, it is shown that, in a structure with the increased thickness deff, a secondary wetting InGaAs layer is produced on top of the QD layer from the growing relaxed large-sized InAs clusters on annealing. A new mechanism of formation of large-sized QDs characterized by a large “aspect ratio” is suggested. The mechanism involves the 2D–3D transformation of the secondary InGaAs layer in the field of elastic strains in previously formed QDs. The specific feature of the array of QDs is the coexistence of three populations of different-sized QDs responsible for the multimode photoluminescence in the range from 1 to 1.6 μm. The potentialities of such structures for infrared photoelectric detectors operating in the range from 1–2.5 μm at room temperature are analyzed.