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The morphology of supermultiperiod Al0.3Ga0.7As/GaAs superlattices grown by molecular-beam epitaxy has been determined using X-ray reflectometry (including the one on a synchrotron source) and photoluminescence. The layer thicknesses of a superlattice with 100 periods determined in laboratory and synchrotron studies correlate with an error of ~1%. Reflection peaks, which are not observed in measurements on a diffractometer and are likely related to the technological growth features of these structures, are revealed on a synchrotron beginning with high (>4–5) Bragg orders. It is analytically shown that these peaks correspond to modulation in the superlattice with a period that is three to five times larger and characterize the thickness dispersion over the structure depth of a few percent. [ABSTRACT FROM AUTHOR]

A design of terahertz (THz) radiation source has been developed based on an AlGaAs/GaAs superlattice grown by molecular-beam epitaxy. The gain and optical loss level are calculated, and the source parameters at which THz generation can be implemented are determined. The resonance behavior of gain, caused by strong mixing of tunnel-coupled electronic states, is investigated. [ABSTRACT FROM AUTHOR]

Elastically strained supermultiperiod (100–1000 periods) AlGaAs/GaAs superlattices with different doping levels and slightly differing period thicknesses have been investigated. The proposed technique of characterization consisting of combined application of deep X-ray reflectometry based on a rigorous calculation method, as well as the well-known method of high-resolution X-ray reflectometry, has made it possible to investigate 100-period structures with 2-nm-wide Al0.3Ga0.7As barriers and 10-nm-wide GaAs wells and determine with a high accuracy the layer thicknesses and spread of interfaces. This achievement can be considered as a first step in further analysis of thick structures using bright synchrotron radiation source. The difference between the expected and obtained by the proposed method layer thicknesses is several percent, including that for samples with a high doping level (up to 1018 cm–3). All supermultiperiod structures are characterized by sharp interfaces with a standard deviation of about 0.1 nm. Based on the obtained data on the thicknesses, one can accurately determine the layer compositions using high-resolution X-ray diffraction. [ABSTRACT FROM AUTHOR]

The results of studies of photochemical etching processes, which were carried out without applying external voltage, for structures with Ga- and N-polar GaN layers synthesized by molecular-beam epitaxy with the plasma activation of nitrogen are reported. It is shown that the etching rates of layers with different polarities are markedly different. At the same time, the use of gold-based masks instead of titanium-based ones for the etching of GaN layers also provides a means for increasing the rate of layer etching. [ABSTRACT FROM AUTHOR]

The results obtained in a study of the synthesis of n+-GaN layers by plasma-assisted molecular-beam epitaxy on GaN/c-Al2O3 templates are reported. In particular, a method is developed for the pre-epitaxial cleaning of the GaN surfaces of templates to remove foreign atoms. It is shown that, to form GaN layers of comparatively good quality, including those doped with silicon up to ~4.6 × 1019 cm–3, GaN template surfaces should be pre-epitaxially cleaned in a flow of activated nitrogen particles, with the substrate temperature increased from TS = 400 to 600°C and the substrate surface subsequently exposed to a flow of activated nitrogen at a fixed value of TS = 600°C for 1 h. After that the substrate temperature should be raised to TS = 700°C and the GaN surface finally cleaned by means of a procedure for gallium deposition/desorption. [ABSTRACT FROM AUTHOR]

The detailed study of GaAs nanowires synthesized by molecular beam epitaxy performed by scanning electron microscopy allowed to reveal the presence of specific contrast in the images obtained. To understand the causes of the phenomenon the transmission electron microscopy of nanowire crystal structure was carried out. The results showed that it could be caused by the segments having polytypic crystal phase. It was also confirmed by the modelling of the electron beam scattering on such nanowire arrays. [ABSTRACT FROM AUTHOR]