V. A. Vekshin

Mie Resonances, Infrared Emission, and the Band Gap of InN

Mie resonances due to scattering or absorption of light in InN-containing clusters of metallic In may have been erroneously interpreted as the infrared band gap absorption in tens of papers. Here we show by direct thermally detected optical absorption measurements that the true band gap of InN is markedly wider than the currently accepted 0.7 eV. Microcathodoluminescence studies complemented by the imaging of metallic In have shown that bright infrared emission at 0.7-0.8 eV arises in a close vicinity of In inclusions and is likely associated with surface states at the metal/InN interfaces.

Transmission Electron Microscopy of GaN Columnar Nanostructures Grown by Molecular Beam Epitaxy

The GaN columnar crystals of nanometric sizes have been grown by molecular beam epitaxy with high-frequency plasma initiation of nitrogen discharge. The types and distribution of defects in these nanostructures on the (0001) sapphire substrates are studied by transmission electron microscopy (TEM). It is revealed that inversion domains begin to form almost at the interface irrespective of the presence of an initial low-temperature buffer layer. The critical diameter of dislocation-free columns, their density, and mean sizes are determined. It is shown that the low-temperature buffer layer affects the density of dislocations, their spatial distribution, and the mean sizes of columns. The nanosizes of grown crystals suggest a further use of these crystals and the growth method for producing molecular-beam epitaxial quantum-size objects (quantum dots and wires) in a promising AlGaInN system.

Nanometric-scale fluctuations of intrinsic electric fields in GaN/AlGaN quantum wells with inversion domains

Strain and electric field fluctuations in regions of different polarities in GaN/AlGaN quantum well (QW) structures of dominant N-polarity with inversion domains (IDs) split the photoluminescence (PL) emission into two bands. Micro-PL and time-resolved PL studies reveal strong inhomogeneity of the array of the IDs, where essential parameters, such as strain, electric fields, and sizes are fluctuating quantities. We demonstrate also that the ID formation decreases the intrinsic electric field magnitudes.

Coaxial rf-magnetron nitrogen activator for GaN MBE growth

Abstract Novel compact coaxial magnetron nitrogen activator with a radio frequency (rf) capacitively-coupled discharge has been used for the first time for GaN molecular beam epitaxial growth on different substrates, including GaAs(113). Optical emission spectra of the discharge have been studied as a function of nitrogen flow rate, rf power, and magnetic field, focusing on first negative (391 nm) and second positive (380 nm) lines associated with nitrogen molecular ions and excited molecules, respectively. Optimization of the activator parameters and distance of the discharge zone from the substrate resulted in GaN growth rate as high as 0.5 μm h −1 at a 350 l s −1 pumping speed.

X-ray diffractometric study of the influence of a buffer layer on the microstructure of molecular-beam epitaxial InN layers of different thicknesses

Thin layers of InN are grown by molecular beam epitaxy on (0001) sapphire substrates. The influence of thin (15 nm) InN buffer layers and their temperature treatment on the structural quality of the grown layers is investigated by double-crystal and triple-crystal x-ray diffractometry. It is revealed that the preliminary high-temperature (900°C) annealing of the buffer layer leads to a notable improvement in the quality of the layers grown on this buffer. The densities of vertical screw and vertical edge dislocations decrease (to 1.9×108 cm−2 and 1.3×1011 cm−2, respectively) with an increase in the distance from the interface (by ∼1 µm).