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The growth features of GaN nanorods on patterned c-sapphire substrates with a regular microcone array having a different density and base diameter in the ranges of (1–5) × 107 cm–2 and 2.5–3.5 μm, respectively, are investigated. The kinetics is studied and the selective-growth regimes are determined for single GaN nanorods with a diameter of 30–100 nm at the vertices of microcones under radically lower growth rates on their slopes. The effect of the configuration of microcones, the substrate temperature, the roughness of the initial surface, and the presence of indium as a surfactant on the degree of growth selectivity is investigated.

The possibility of fabricating hybrid metamorphic heterostructures for vertical-cavity surfaceemitting lasers working in the 1300-nm spectral range is demonstrated. The metamorphic semiconductor part of the heterostructure with a GaAs/AlGaAs distributed Bragg reflector and an active region based on InAlGaAs/InGaAs quantum wells is grown by molecular-beam epitaxy on a GaAs (100) substrate. The top dielectric mirror with a SiO2/Ta2O5 distributed Bragg reflector is formed by magnetron sputtering. The spectra of the room-temperature microphotoluminescence of these vertical-cavity surface-emitting laser heterostructures are studied under 532-nm excitation in the power range of 0–70 mW (with a focused-beam diameter of ~1 μm). The superlinear dependence of the photoluminescence intensity on the excitation power, narrowing of the photoluminescence peaks, and a change in the modal composition may be indications of lasing. The results obtained give evidence that the technology of the metamorphic growth of heterostructures on GaAs substrates can be used for the fabrication of vertical-cavity surface-emitting lasers working in the 1300- nm spectral range.

AbstractWe report on fabrication and studies of composite heterostuctures consisting of an Al_0.55Ga_0.45N/A_l0.8Ga_0.2N quantum well and surface Al nanoislands, grown by plasma-assisted molecularbeam epitaxy on c-sapphire substrates. The influence of a substrate temperature varied between 320 and 700ºC on the size and density of the deposited Al nanoislands is evaluated. The effect of Al nanoislands on decay kinetics of the quantum well middle-ultraviolet photoluminescence has been investigated by time resolved photoluminescence. The samples with the maximum density of Al nanoislands of 10^8 cm^–2 and lateral dimensions in the range of 100–500 nm demonstrated shortening of the photoluminescence lifetime, induced by interaction of the emitting quantum well and the plasmonic metal particles.

The spectral, threshold, and power characteristics of a microdisk laser 31 μm in diameter with an active region based on InAs/InGaAs quantum dots, operating in the continuous-wave (cw) mode at room temperature are studied. The minimum threshold current density is 0.58 kA/cm2, the subthreshold linewidth of the whispering-gallery mode is 50 pm at a wavelength lying in the range of 1.26–1.27 μm. The total power emitted into free space reaches ~0.1 mW in the cw mode, whereas the radiation power of the whispering-gallery modes is ~2.8%.

The polarization characteristics of 850-nm vertical-cavity surface-emitting lasers (VCSELs) with intracavity contacts and a rhomboidal oxide current aperture are studied. It is found that radiation polarization is always directed along the minor diagonal of the rhomboidal aperture (along the [ $$\overline 1 $$ 10] direction) for all single-mode VCSELs. The numerical simulation of carrier transport does not reveal the significant anisotropy of carrier injection to the active region. Furthermore, an analysis of the spatial distribution of the fundamental mode for two orthogonal polarizations within an effective waveguide model shows close transverse optical-confinement factors. Optical loss anisotropy in the asymmetric microcavity and/or gain anisotropy in the strained active region are the most likely mechanisms responsible for fixing the polarization.

Microdisk injection lasers on GaAs substrates, with a minimum diameter of 15 μm and an active region based on InAs/InGaAs quantum dots, are fabricated. The lasers operate in the continuous-wave mode at room temperature without external cooling. The lasing wavelength is around 1.27 μm at a minimum threshold current of 1.6 mA. The specific thermal resistance is estimated to be 5 × 10–3 °C cm2/W.

The thermal resistance of AlGaAs/GaAs microlasers of the suspended-disk type with a diameter of 1.7–4 μm and InAs/InGaAs quantum dots in the active region is inversely proportional to the squared diameter of the microdisk. The proportionality factor is 3.2 × 10−3 (K cm2)/W, and the thermal resistance is 120–20°C/mW.

Single-spatial-mode semiconductor vertical-cavity surface-emitting lasers (VCSELs) with a non-planar upper (output) dielectric distributed Bragg reflector (DBR) for the 850 nm spectral region are fabricated. The suggested design provides stable single-mode generation in the entire range of working currents, limited by overheating of the active region. Devices with intracavity contacts and a comparatively large current-aperture diameter (5–6 μm) exhibit single-mode lasing at a wavelength of 840–845 nm in the continuous-wave mode at room temperature with threshold currents of 1.2–1.3 mA, a differential efficiency of 0.5–0.55 mW mA−1, and anoutput power of up to 2 mW.

The influence of the carrier gas, trimethylgallium flow, and growth time on the character of the selective epitaxy of GaN in stripe windows oriented along the crystallographic direction 〈 $\bar 1$ 100〉 GaN for various widths of the mask between the stripes is studied. It is shown that the addition of nitrogen in the reactor atmosphere leads to changes in the form of the stripes in the case of wide (40 μm) mask from a rectangular form restricted by a {1 $\bar 1$ 20} lateral face to a trapezoidal form restricted by a {1 $\bar 1$ 22} lateral face. It is also shown that during growth in the nitrogen-hydrogen mixture, the gallium flow starts to considerably affect the form of the growing stripes. It is shown that the process is significantly unstable, which leads to a noticeable variation in the form type as the transverse section of the stripe increases.

A nondestructive method for measuring the thicknesses of epitaxial layers of Al x In1 − x Sb alloys based on interference effects in reflectance spectra measured in a wide wavelength range (1–28 μm) is implemented. The studied 0.9–3.3 μm thick Al x In1 − x Sb layers are grown on highly lattice-mismatched GaAs substrates by molecular beam epitaxy. The found thicknesses are in good agreement with the independent data of scanning electron microscopy. The spectral dependence of the refractive index n(E) of Al x In1 − x Sb layers is measured both for the regions of transparency and fundamental absorption. The refractive index for the case of E < E 0 was calculated by a double-oscillator model using a refined experimental dependence of the band gap on the composition E 0(x). The experimental data on the n(E) of Al x In1 − x Sb for energies E > E 0 are found based on the interference pattern.

Lasing at a wavelength of >1.3 μm has been achieved at temperatures of up to 380 K in a ring microlaser (diameter of 6 μm) with an active region based on InAs/InGaAs quantum dots.

Structural and optical properties of InAlN/GaN distributed Bragg reflectors grown by MOCVD on sapphire substrates are studied. The influence of growth conditions and thicknesses of the InAlN layers on structural properties of distributed Bragg reflectors is studied. It is shown that optimization of the conditions of epitaxial growth makes it possible to design InAlN/GaN distributed Bragg reflectors with a reflectance of more than 99% and a reflection maximum in the wavelength range of 460-610 nm.

The effectiveness of magnetron-sputtering deposition in an Ar-N2 plasma-forming mixture as a technique for the fabrication of arrays of GaAs1 − xNx nanowires (NWs) with typical diameters from 10 to 200 nm and lengths up to 3000 nm is demonstrated. Dependence of the growth character of NW on the parameters of the synthesis process, such as the size of Au droplets, deposition rate, and crystallographic orientation of the surface and the temperature of the substrate, is investigated. Analysis of the dependence of NW height on their diameter demonstrates that growth occurs predominantly by the diffusion mechanism. The nitrogen content is kept stable for growth temperatures in the range 400–500°C, being as high as 2.7%. For the substrate temperatures in the range 530–600°C, an abrupt drop in the nitrogen content in the alloy takes place. In the photoluminescence (PL) spectra of the samples obtained, a red shift of the emission band is observed, which is related to an increase in the nitrogen content. The growth-temperature dependence of the position of the luminescence band and the nitrogen content is determined. It is found that the PL intensity of samples with GaAsN NWs containing 2.7% nitrogen increases by a factor of 5–10 as compared to samples with planar layers, which is explained by the absence of structural defects in NWs.