Yu. V. Khabarov

Optical and transport properties of short period InAs/GaAs superlattices near quantum dot formation

We have investigated the optical and transport properties of short-period superlattices of InAs/GaAs, grown by molecular beam epitaxy, with different numbers of periods (3 ≤ N ≤ 24) and a total thickness of 14 nm. Band structure calculations show that these superlattices represent a quantum well with average composition In0.16Ga0.84As. The electron wavefunctions are only slightly modulated by the superlattice potential as compared to a single quantum well with the same composition, which was grown as a reference sample. The photoluminescence, the resistance, the Shubnikov–de Haas effect and the Hall effect have been measured as a function of the InAs layer thickness Q in the range of 0.33 ≤ Q ≤ 2.7 monolayers (ML). The electron densities range from 6.8 to 11.5 × 1011 cm−2 for Q ≤ 2.0 ML. The photoluminescence and magneto-transport data show that only one sub-band is occupied. When Q ≥ 2.7 ML, quantum dots are formed and the metallic type of conductivity changes to variable range hopping conductivity.

Structural characterization of interfaces in the AlxGa1−xAs/GaAs/AlxGa1−xAs heterostructures by high-resolution X-ray reflectometry and diffractometry

The structural properties of multiplayer AlxGa1−xAs/GaAs/AlxGa1−xAs systems (x ≈ 0.2) grown on GaAs(001) substrates are studied by the methods of double-crystal X-ray diffractometry and reflectometry. The depth profiles of deformation, amorphization, and density of the layers are obtained. It is shown that despite small differences (5–7%) in the densities of the AlxGa1−xAs layers and the substrate and the small thickness of the AlAs layer (1–2 nm) separating the GaAs quantum well, it is possible to reconstruct the heterostructure model by the method of X-ray reflectometry and to determine the thickness of the transitional layers at a resolution of 0.1–0.2 nm. It is also established that the reflectometry data obtained complement the X-ray diffraction data considerably and allow one to estimate the roughness and the character of the aluminum distribution at the interfaces.

Lateral electronic transport in short period InAs/GaAs superlattices at the threshold of quantum dot formation

Temperature dependences of resistance at 0.7 K<T<300 K, the Hall and Shubnikov-de Haas effects in magnetic fields of up to 40 T, photoluminescence (PL), and morphology of a heterointerface (using an atomicforce microscope) of short-period InAs/GaAs superlattices were investigated. The investigations were carried out for a region of subcritical and critical thickness Q=2.7 monolayers (ML) of InAs. Upon exceeding the critical thickness, the self-organized growth of InAs quantum dots (QDs) set in. The formation of QD layers upon exceeding the critical thickness of InAs Q=2.7 ML is accompanied by a transition of conductivity from metallic to hopping. It is found that at InAs layer thicknesses of Q=0.33 ML and Q=2.0 ML, the PL intensities and electron mobilities in the structures have clearly pronounced maxima. Anisotropy of conductivity, which depends on the thickness of the deposited InAs layers, was observed.

Properties and structure of GaAs films grown by molecular beam epitaxy on GaAs substrates with the (100), (111)A, and (111)B orientations

The structural perfection of GaAs epitaxial films grown by molecular beam epitaxy on substrates with the (100), (111)A, and (111)B orientations is investigated by double-crystal and triple-crystal x-ray diffractometry. It is found that the ratio γ of the molecular fluxes of arsenic and gallium has a strong influence on the structural quality of the epitaxial films. The optimum values of the parameter γ are found for each of the substrate orientations (100), (111)A, and (111)B.

Influence of crystal orientation of the growth surface due to molecular beam epitaxy on the optical properties of Si-doped GaAs layers

AbstractPhotoluminescence (PL) spectra of GaAs (100), (111)A and (111)B layers grown by molecular-beam epitaxy at different ratios of the partial pressures

Studies of physical phenomena in semiconductor nanostructures using samples with laterally nonuniform layers: Photoluminescence of tunneling-coupled quantum wells

{{P_{As_4 } } \mathord{\left/ {\vphantom {{P_{As_4 } } {P_{Ga} }}} \right. \kern-\nulldelimiterspace} {P_{Ga} }} = \gamma

In x Ga 1–xAs Strained-Layer Quantum Well in a Pseudomorphic Heterostructure: High-Resolution XRD Characterization for Different Quantum-Well Thicknesses

are investigated. Depending on the crystal orientation and γ values, either two PL bands (B-Si bands) or a single PL B-band are observed. The B-band corresponds to band-to-band radiative recombination (e→h) and the Si band is attributed to optical transitions between the conduction band and the Si acceptor states (e→A). The observed variations of the PL spectra and of the type and magnitude of the electrical conductivity as functions of the orientation and γ value are interpreted in terms of changes in the Si-acceptor concentration and their energy spectrum as well as a change in the ratio of the concentrations of the Si donor and acceptor states. These results are explained in the framework of the kinetic approach based on the multiplicity (energy) of the dangling chemical bonds on the different surfaces, with the influence of the molecular flux densities taken into account.

A study of the electrical and optical properties of Si delta-doped GaAs layers grown by MBE on a (111)A GaAs surface misoriented toward the [2\(\bar 1\bar 1\)] direction

Photoluminescence of a structure based on GaAs with δ-doped n-type layers is studied experimentally at 77 K in the context of a previously suggested spectral-correlative method for investigating semiconductor structures with laterally nonuniform layers. This method makes it possible to study (for the same sample) the features of the observed multicomponent photoluminescence spectrum in relation to two parameters, i.e., the distance between the δ-doped layers and the width of a narrow InGaAs quantum well located between these layers. The results obtained make it possible to relate the observed exponential increase in the intensity of photoluminescence from the region of δ-doped layers as these parameters are varied to the variation in the ratio between the concentration of the holes laterally localized in the minimums of the fluctuation potential and that of free two-dimensional holes. An effect of stabilization of the energy position of the photoluminescence spectral lines is observed; this effect is related to the localization of holes in the potential well between the δ-doped layers. The experimental data obtained are consistent with the results of our numerical calculations.