Alexander V. Uvarov

In this work, the physical origin of the persistent photoconductivity (PPC) effect in InP films synthesized by plasma-enhanced atomic layer deposition (PE-ALD) at 380 °C was investigated. Cross-sectional TEM confirmed the formation of a nanocrystalline cubic InP layer on Si, while Raman spectroscopy revealed comparable crystalline characteristics for films grown on Si and fused silica substrates. The photocurrent relaxation kinetics was well described by a stretched-exponential function, indicating a broad distribution of characteristic relaxation times associated with heterogeneous trapping and recombination processes. A significant difference was revealed between the activation energy of equilibrium electron transport (0.114 ± 0.003 eV) and the macroscopic recombination barrier for nonequilibrium carriers (0.270 ± 0.058 eV). Hall-effect measurements showed that the PPC is predominantly associated with an increase in electron concentration, rather than changes in carrier mobility. The long lifetime of the photoexcited state is consistent with a barrier-mediated mechanism of spatial separation of electron hole pairs associated with grain boundaries.

The fabrication of periodical GaN/InP structures on Si with a wide layer thickness variation (from submonolayer digital alloys to multilayer stacks) using low-temperature plasma technology is explored in the paper. The proposed technology, which combines the approaches of plasma-enhanced chemical vapor deposition (PECVD) and atomic-layer deposition, was realized at 380 °C using a standard capacitively coupled plasma PECVD reactor. Trimethylindium, trimethylgallium, phosphine, and nitrogen (N2) were used as sources of In, Ga, P, and N, respectively. A series of GaN/InP periodical structures were grown on an Si (001) substrate with a previously deposited thin (7 nm) GaP buffer layer. A structure grown as submonolayer digital alloys (a short-period superlattice with GaN and InP thicknesses of 0.3 and 0.6 nm) exhibits a crystal structure consisting of both microcrystalline and epitaxially oriented grains that follow the orientation of the Si substrate. The vertical size of the grains corresponds to the total GaN/InP periodical structure’s thickness. However, with an increase in the GaN barrier layer thickness to 1.5–3 nm, the GaN undergoes amorphization. This leads to the formation of a layered structure containing misoriented nanocrystalline InP layers embedded between amorphous GaN layers. This effect is associated with significant incorporation of phosphorus into GaN layers, which are formed using a N2 + H2 gas mixture plasma. Indeed, the H2 plasma used for GaN deposition interacts with the phosphorus deposited on the chamber wall during the previous InP step. The discovered issue should be taken into account for plasma technology development of multilayer structures, which included a combination of III-nitride/III-phosphide.

Boron phosphide (BP) thin films are potential selective contact layers for photovoltaic (PV) devices. However, lower deposition temperatures are preferred in the fabrication of many PV devices, such as solar cells, to reduce their cost. Here, boron phosphide layers were grown on silicon (100) substrates using the standard plasma-enhanced chemical vapor deposition (PECVD) and time-modulated PECVD methods with trimethylboron [B(CH3)3, TMB] and phosphine precursors. The effect of plasma power and Ar addition on structural properties and chemical composition is investigated, while material properties are analyzed by transmission electron microscopy. Chemical characterization by the electron diffraction x-ray spectroscopy method showed high carbon content in the BP layer. Electron energy loss spectroscopy demonstrated almost stoichiometric B and P (1:1) content. Raman spectroscopy of annealed samples showed an increase in carbon-related peaks, therefore indicating that annealing does not lead to the crystallization of boron phosphide. Thus, using TMB as a precursor of boron leads to carbon contamination in both standard and time-modulated modes. Optical emission spectroscopy showed that the low-temperature growth of BP without plasma (Ar or phosphine) assistance using TMB is impossible. We conclude that there is a need to investigate other boron precursors for boron phosphide low-temperature growth to avoid carbon contamination in BP films.

This paper investigates the optical and electrical properties of ITO films for their application as a transparent contact electrode to NiO films. The films were fabricated by magnetron sputtering at various parameters of the discharge power and oxygen content in the working gas mixture. Structural analysis showed an increase in the crystallinity of the films during their subsequent annealing. The films demonstrate high conductivity and transparency with an absorption edge higher than that of NiO films. The results of the study show a high potential for using ITO films to create a transparent electrode to NiO layers.

Investigations of atomic-layer deposition of GaP layers on Si substrates with different orientations and with different preliminary surface treatment have been carried out. The deposition of GaP was carried out by the method of plasma enhanced atomic-layer deposition using in situ treatment in argon plasma. It was shown that at the initial stage of the growth of GaP layers on precisely oriented (100) Si substrates and with misorientation, two-dimensional growth occurs both after chemical and plasma surface treatment. Upon growth on (111) substrates, after plasma treatment of the surface, a transition to three-dimensional growth is observed, at which the size of islands reaches 30–40 nm. The smallest root-mean-square roughness of the surface of the growing GaP layers (<0.1 nm) was achieved for (100) substrates with a misorientation of 4°. The GaP layers grown on (100) substrates had a roughness of ~0.1 nm, and on substrates with the (111) orientation—0.12 nm. It was found that the surface treatment of Si substrates with the (100) orientation in hydrogen plasma leads to a slight increase in the surface roughness of growing GaP layers (0.12–0.14 nm), which is associated with the effect of inhomogeneous etching of silicon in hydrogen plasma. When treating the (100) silicon surface in argon plasma, the surface roughness does not change significantly in comparison with the chemical surface treatment. On the surface of substrates with preliminary deposition of an epitaxial Si layer with a thickness of 4 nm, the morphology of GaP layers is the same as in the case of using hydrogen plasma.

We consider structure with single quantum well InP 5 nm thick grown by vapor phase epitaxy on n-GaP wafer. By classical capacitance-voltage profiling of Schottky diode on sample and electrochemical profiling, electron accumulation were detected in InP layer so existence of quantum well is confirmed. Results of admittance spectroscopy and deep-level transient spectroscopy showed defect formation in GaP layers above InP with energy position of Ec-0.21 eV, 0.30 eV и 0.93 eV.

This paper presents the results of investigation of gold nanoparticle array formation on GaN surface and its plasmon effect. Gold nanoparticles are formed on GaN layer grown by molecular beam epitaxy (MBE) by solid-state dewetting technique both in the air at atmospheric pressure and under vacuum conditions. The influence of the thickness of as-deposited gold film and annealing ambient on the size and spatial distribution of nanoparticles was studied. Investigation of optical characteristics showed the appearance of the surface plasmon resonance effect. The results reveal the possibility to increase the efficiency of GaN-based optoelectronic devices by Au nanoparticle arrays.

The results of the study of the optical properties of low-density InGaPAs quantum dots, as well as the effect of low temperatures and thermal annealing parameters on their optical and structural properties were presented. InGaPAs quantum dots were formed by substituting phosphorus with arsenic in InGaP layer directly during epitaxial growth. The optical properties of InGaPAs quantum dots were studied by photoluminescence (PL) spectroscopy. Photoluminescence spectra at liquid nitrogen temperature (–196 °С) made it possible to determine the features of nonradiative recombination in heterostructures. The heterostructures were subjected to short-term thermal annealing at temperatures of 600 and 650 °C for 2 min to estimate the effect of annealing on the optical and structural properties of quantum dots. It was shown that at –196 °С the contribution of nonradiative recombination can be considered insignificant for the entire measured range of pumping power rage but at temperatures above –73 °С, the contribution of nonradiative Shockley-Reed recombination can be observed. Rapid thermal annealing of InGaPAs quantum dots led to reduce the number of point defects and growth of PL intensity. InGaPAs quantum dots and substitution method can find their application in the creation of single photon sources. The presented experimental results should be considered for implementing such sources, especially for optimizing the width and intensity of the radiation line.