Maksim S. Sobolev

Objective: The aim of this work is to study bulk GaPN and GaPNAs layers grown by molecular beam epitaxy on silicon substrates. The optical properties of the heterostructures were investigated using photoluminescence. The technique of time-resolved photoluminescence (or photoluminescence kinetics) was employed to evaluate the carrier lifetime in bulk GaPN and GaPNAs layers.Experimental: An investigation of the influence of the buffer layer on the heterostructure characteristics was conducted. The photoluminescence intensity in the bulk GaPN layer was found to be virtually identical for heterostructures employing either a buffer layer grown by Migration-Enhanced Epitaxy (MEE-GaP buffer) or a GaP buffer layer grown with a gradual temperature ramp from 450 to 600 °C.Conclusion: It was shown that the lifetime of minority carriers in the bulk GaPN layer grown on a silicon substrate is determined to a greater extent by defects introduced during the nitrogen incorporation into the GaP lattice, rather than by defects caused by growth on silicon substrate

Purpose: The paper describes structural features of the growth of GaN layers synthesized by plasma-assisted molecular beam epitaxy on silicon substrates without substrate nitridation and without the formation of an aluminum-containing interlayer.Experimental: High-resolution X-ray diffractometry was used to show that the proposed method can be used to grow strainfree GaN films. It was found that in GaN layers grown directly on the Si substrate after its surface passivation by Ga atoms, the value of residual strain was at 300 MPa, while the use of indium atoms as a surfactant during the growth of the GaN layer resulted in a higher residual strain.Conclusions: The obtained results are important for understanding the viability of the proposed approach for the formation of GaN layers directly integrated with Si without substrate nitridation and the formation of an aluminum-containing buffer. This method opens new opportunities for designing AIIIN-based optoelectronic devices

This paper investigates the effectiveness of metamorphic InAlAs buffer layers with linear and root-like dependence of the In mole fraction in the composition for the growth of bulk In0.83Ga(Al)0.17As layers on InP substrates. The analysis of the X-ray diffraction reciprocal space maps showed that in both cases In0.83Ga(Al)0.17As layers were partially strain-free. One of the mechanisms of strain relaxation during the growth of the linearly graded buffer layer is the rotation of the crystal lattice, while the mechanism of strain relaxation during the growth of the convex-graded buffer layer is a 0.82° tilt of the crystal lattice without any rotation. According to the images obtained by transmission electron microscopy, the density of threading dislocations in the upper InGaAs layers grown on the buffer layer with a linear composition gradient is ~ 5·108 cm–2

A room-temperature study of the optical transitions in GaAs/Al_xGa_1–xAs super-multiperiod superlattices (SMP-SLs) grown by molecular beam epitaxy was performed by photoreflectance spectroscopy. The development of devices based on high quality semiconductor SMP-SLs requires a comprehensive understanding of the energy miniband formation in the grown samples. Existing theoretical approaches to modeling the energy spectrum of SMP-SLs do not always correctly describe one in real structures due to the lack of correct information about the energy spectrum. The combination of the results of photoreflectance spectroscopy with the data obtained within the framework of the 8-band Kane theoretical model allows us to get a detailed interpretation of all optical transitions, that was confirmed by the results of the detailed study of GaAs/Al_xGa_1–xAs SMP-SL samples with different quantum wells and barriers widths.

The results of investigation of the gain properties of 1300 nm vertical-cavity surface-emitting lasers active regions based on In0.60Ga0.40As/In0.53Al0.20Ga0.27As superlattices and threshold characteristics comparison of superlattices and highly lattice mismatched In0,74Al0,16Ga0,10As quantum wells are presented. The heterostructure of injection lasers with an In0.60Ga0.40As/In0.53Al0.20Ga0.27As superlattice was grown by molecular beam epitaxy. Mesa structure of injection lasers was obtained by selective liquid etching followed by the application of ohmic contacts. The formation of injection lasers with various cavity lengths is performed using the method of manually cleaving mirrors. The output characteristics were measured in a pulsed mode using a large area calibrated germanium photodiode. Spectral characteristics were measured using a spectrophotometer based on monochromator. The achieved threshold characteristics (modal gain about 40 cm–1, transparency current density about 650 A/cm2, internal optical losses about 8 cm–1) of injection lasers based on In0.60Ga0.40As/In0.53Al0.20Ga0.27As superlattices with low lattice mismatch InGaAs layers are comparable to previously presented lasers based on active regions with strongly strained In0,74Al0,16Ga0,10As quantum wells. The characteristic temperatures T0 and T1 were 60 K and 87 K for injection lasers with a cavity length of 1 mm. An increase in the frequency of small-signal modulation of vertical-cavity surface-emitting lasers and their temperature stability is associated with the use of highly strained In0.60Ga0.40As/In0.53Al0.20Ga0.27As superlattices. The proposed active regions based on InGaAs-InP superlattices have the potential to be used in the development of vertical-cavity surface-emitting lasers in the 1300 nm spectral range. The findings of this work can be applied in the realization of experimental species and optimization of modulation parameters for vertical-cavity lasers operating in the 1300 nm wavelength range.

Due to a large number of applications in the near and short-wave IR spectrum and a relatively high detectivity, PIN photodiodes based on epitaxial InGa(Al)As/InP heterostructures are of a great scientific interest. The operational spectral range of such photodetectors is up to 2.6 μm. However, to reach such wavelengths it is necessary to synthesize heterostructures with metamorphic buffer layers. In our study, we investigated the current-voltage and capacitance–voltage characteristics of PIN photodiodes based on InGa(Al)As/InP heterostructures with an original metamorphic buffer layer and an In0.83Ga0.17Asabsorbing layer grown by means of molecular beam epitaxy. The photodiode chips were formed using standard post-growth processing techniques. The diameter of the photosensitive area of the obtained diodes was 140 μm. The dark currents and the shunt resistance were ~ 300 nA and ~ 25 kΩ at the voltage of -10 mV respectively. Therefore, the suggested metamorphic buffer layer effectively eliminates threading dislocations in the active area of the heterostructure. The obtained heterostructures with metamorphic buffer layers can be used to produce IR photodetectors for the spectral range of 2.2-2.6 μm

The addition of a few percent of nitrogen to GaP or GaPAs allows obtaining GaPNAs solid solutions that are lattice-matched to the silicon substrate over a wide range of band gaps, which makes it possible to obtain optoelectronic silicon integrated circuits. However, materials with a small fraction of nitrogen are understudied due to the difficulty in epitaxial growth of quaternary solid solutions with three materials of group V. The purpose of the study was the investigation of the influence of the substrate temperature during the epitaxial growth of dilute nitride materials (GaPN solid solution and GaPNAs/GaP(N) superlattices) on their optical properties, as well as the influence of the growth temperature and superlattice design on the bandgap of the resulting material. It was shown that there is an optimal growth temperature for samples: at temperatures below the optimal, non-radiative recombination at defects predominates, and at a temperature higher than the optimal one, the solid solution of the GaPN layer material decomposes into components with a larger and smaller fraction of nitrogen. Studies were also carried out on the decay of photoluminescence intensity over time in the studied structures at room temperature, which allowed us to evaluate the influence of growth parameters and structure design on the lifetime of nonequilibrium charge carriers. The best lifetime for structures with superlattices was obtained for the GaPNAs/GaPN superlattice and amounted to ~0.2 ns. As a result, the optimal growth temperatures were determined for bulk GaPN layers and for GaPNAs/GaP(N) superlattices, which leads to an increase in the PL intensity and lifetime of the carrier

The paper demonstrates that the technology of plasma-assisted molecular beam epitaxy (PA MBE) can be used to form epitaxially overgrown GaN, n-GaN, and n+-GaN contact layers with a high structural quality on virtual GaN/c-Al2O3 substrates under Ga-enriched conditions at relatively low growth temperatures of ~700 °C. It was shown that the initial stage of growth of the contact layers was accompanied by effective filtration of dislocations threading from the buffer GaN layer of the virtual substrate formed by MOCVD. The values of residual stresses calculated using the data of Raman microspectroscopy indicate a high structural quality of GaN, n-GaN, and n+-GaN contact layers regardless of the level of silicon doping. The contact resistance reduced to the pad width determined using the transmission line method for the structure with n+-GaN contact layer was ~0.11 Ohm·mm and for the n-GaN contact layer it was ~0.5 Ohm·mm

The charge carrier density distribution in uniformly doped AlGaAs/GaAs superlattices with layer thicknesses of 1.5/10 nm and different numbers of quantum wells was studied. Both energy band theory and capacitance–voltage profiling were used to determine the carrier concentration profiles of the structures. During the analysis of the experimental and simulated capacitance–voltage characteristics, it was found that the maximum electron concentrations increase with an increase in the number of quantum wells from ∼ 7.1 ⋅ 10 16 cm − 3 for three wells to ∼ 9.3 ⋅ 10 16 cm − 3 for 25 wells with an overall superlattice doping level of ∼ 10 17 cm − 3 .