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The growth of nanoscale columnar AlxGa1-xN/AlN heterostructures on the surface of silicon substrates using plasma-activated nitrogen molecular-beam epitaxy was investigated in this work. Silicon substrates include atomic-smooth cSi substrate, Si substrate with a transition layer of porous silicon porSi/cSi and a hybrid substrate involving a silicon carbide layer grown with matched substitution of the atoms on the surface of porous silicon SiC/porSi/cSi. A complex analysis performed using a set of structural and spectroscopic techniques demonstrated that the epitaxial growth of the nuclear AlN layer on all types of the substrates in a N-enriched environment resulted in the formation of AlxGa1-xN/AlN heterostructures with a Ga-polar surface, which was realized only on the SiC/porSi/cSi substrate. The layer of AlxGa1-xN on cSi and porSi/cSi substrates was in the state of disordered alloy with an excess of gallium atom content. It was shown that a great difference in the lattice parameters of a substrate–film pair resulted not only in the appearance of a number of various defects but also in a considerable effect on the chemical process of the formation of the alloys, in our case, the AlxGa1-xN alloy. It was shown that nanoscale columns of AlxGa1-xN formed on SiC/porSi/cSi substrate were inclined relative to the c-axis, which was connected with the features of the formation of a SiC layer by the matched substitution of the atoms on the porous Si substrate, resulting in the formation of the inclined (111) SiC facets at the boundary of the (111) Si surface and pores in Si. Optical studies of the grown samples demonstrated that the optical band-to-band transition for the AlxGa1-xN alloy with Eg = 3.99 eVB was observed only for the heterostructure grown on the SiC/porSi/cSi substrate. A qualitative model is proposed to explain the difference in the formation of AlxGa1-xN layers on the substrates of cSi, porSi/cSi and SiC/porSi/cSi. The results obtained in our work demonstrate the availability of using SiC/porSi/cSi substrates for the integration of silicon technology and that used for the synthesis of nanoscale columnar AlxGa1-xN heterostructures using plasma-activated molecular-beam epitaxy with a nitrogen source. [ABSTRACT FROM AUTHOR]

We present the results of experimental studies of the capacitance–voltage (C–V) characteristics and the spectra of deep-level transient spectroscopy (DLTS) of graded high-voltage p+–p0–i–n0 GaAs diodes fabricated by liquid-phase epitaxy at a crystallization-onset temperatures of 900°C from one solution melt due to self doping with background impurities, in a hydrogen or argon atmosphere, before and after irradiation with neutrons. After irradiation with neutrons, the DLTS spectra reveal wide defect-cluster regions with acceptor-like negatively charged traps of the n0-type layer, resulting from the emission of electrons from states located above the middle of the band gap. It is found that the differences in the C–V characteristics of the structures grown in a hydrogen or argon atmosphere are due to the different doses of irradiation of p+–p0–i–n0 GaAs structures and different degrees of compensation of shallow donor impurities by deep traps in the layers. [ABSTRACT FROM AUTHOR]

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]

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 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 photoelectric properties of GaN/SiC/Si(111) and GaN/Si(111) heterostructures grown by plasma-assisted molecular-beam epitaxy under the same growth conditions on identical silicon substrates, but with different buffer layers, are experimentally investigated. The GaN/SiC/Si(111) structure is formed on a Si substrate with the SiC buffer layer grown by a new atom-substitution technique and the GaN/Si(111) structure, on a Si substrate subjected to pre-epitaxial plasma nitridation. The significant effect of carbon-vacancy clusters contained in the SiC layer on the growth of the GaN layer and its optical and photoelectric properties is found. It is experimentally established that the GaN/SiC/Si(111) heterostructure has a higher photosensitivity than the GaN/Si(111) heterostructure. In the GaN/SiC/Si(111) heterostructure, the coexistence of two oppositely directed p–n junctions is observed. One p–n junction forms at the SiC/Si interface and the other, at the GaN/SiC interface. It is shown that the occurrence of an electric barrier in the GaN/Si(111) heterostructure at the GaN/Si(111) heterointerface is caused by the formation of a thin silicon-nitride transition layer during pre-epitaxial plasma nitridation of the Si(111) substrate. [ABSTRACT FROM AUTHOR]

It is shown that single-crystal GaP buffer layers can be formed on a Si substrate by molecular-beam epitaxy, with the 'migration-enhanced epitaxy' procedure applied in the stage in which the nucleating layer is formed. When a GaP layer is produced on a p-type silicon substrate, a p-n junction is created in a natural way between the p-Si substrate and the surface n-Si layer produced by the diffusion of phosphorus into the substrate during the course of the epitaxial growth of GaP. This p-n junction can be used as the first junction of a silicon-based multijunction photovoltaic converter. [ABSTRACT FROM AUTHOR]

The preparation of pure, undoped, high-temperature GaP grown by liquid-phase epitaxy is reported. Results are presented of studies of GaP p-n structures grown at various crystallization initiation temperatures, using the capacitance-voltage (C-V) method and deep-level transient spectroscopy (DLTS). The characteristics of GaP are determined by the low concentration of background impurities and deep-level defects. Measurements of the temperature dependence of the forward branch of the current-voltage characteristic showed that the thermometric characteristic of the diode is linear between -191 and ∼+600 °C. [ABSTRACT FROM AUTHOR]