The Effect of the Method by Which a High-Resistivity GaN Buffer Layer Is Formed on Properties of InAlN/GaN and AlGaN/GaN Heterostructures with 2D Electron Gas

AlGaN/AlN/GaN and InAlN/AlN/GaN structures with 2D electron gas have been grown on sapphire substrates by metal-organic vapor-phase epitaxy. The suppression of the parasitic conductivity of buffer GaN layers was provided either by intentionally raising the density of edge dislocations or by doping with iron (GaN:Fe). It was shown that using GaN buffer layers with a better crystal perfection and more planar surface results in the electron mobility in the 2D channel for carriers becoming 1.2–1.5 times higher.     

Self-assembled silver nanoislands formed on glass surface via out-diffusion for multiple usages in SERS applications

We demonstrate that silver nanoisland film self-assembled on the surface of silver-containing glass in the course of thermal processing in hydrogen is capable to detect 10⁻⁷ M concentration of rhodamine 6G in water using surface enhanced Raman spectroscopy (SERS) technique. The film can be multiply restored on the same glass substrate via annealing of the glass in hydrogen. We showed that the film can be self-assembled after as much as ten circles of the substrate cleaning followed by annealing. The proposed technique of the silver nanoisland film formation enables multiple usage of the same glass substrate in SERS experiments.     

Local triboelectrification of an n-GaAs surface using the tip of an atomic-force microscope

The method of scanning Kelvin-probe microscopy is used to show that the effect of triboelectrification is observed when the tip of an atomic-force microscope interacts with the surface of n-GaAs epitaxial layers. The sign of the change in the potential indicates that the sample surface after triboelectrification becomes more negative. The observed specific features of the phenomena can be attributed to the thermally activated generation of point defects in the vicinity of the sample surface due to deformation caused by the tip.     

Characterization of defects in colloidal CdSe nanocrystals by the modified thermostimulated luminescence technique

The temperature dependencies of the luminescence spectra of 5-nm-diameter CdSe semiconductor nanocrystals synthesized by colloidal-chemistry methods are investigated. The two bands observed in these spectra around 2.01 and 1.37 eV correspond to band-to-band transitions and luminescence of defect states, respectively. A model explaining the temperature behavior of the luminescence band intensities both upon cooling and heating is put forward. A new modification of spectrally resolved thermostimulated luminescence technique making it possible to determine the activation energies and the character of traps responsible for the temperature dependence of the luminescence intensities is suggested. This technique is used to obtain the activation energies of the emission and capture of electrons at traps (190 and 205 meV, respectively) and to determine the depth of the electron level (57 meV) responsible for luminescence in the 1.37-eV region.     

Double-cross epitaxial overgrowth of nonpolar gallium nitride layers

Epitaxial gallium nitride (GaN) structures have been manufactured by the lateral overgrowth technology, whereby GaN epilayers are grown in stripe windows on a partly masked initial GaN layer. It is established that in addition to the traditional orientation of stripes across the c axis, the process is also possible for the stripes oriented at 45° relative to this axis. In this case, two lateral overgrowth processes in mutually perpendicular directions can be performed, which would significantly reduce the relative area of imperfect material formed over windows in the mask.     

Capacitance study of electron traps in low-temperature-grown GaAs

Electron traps in GaAs grown by MBE at temperatures of 200–300°C (LT-GaAs) were studied. Capacitance deep level transient spectroscopy (DLTS) was used to study the Schottky barrier on n-GaAs, whose space-charge region contained a built-in LT-GaAs layer ∼0.1 μm thick. The size of arsenic clusters formed in LT-GaAs on annealing at 580°C depended on the growth temperature. Two new types of electron traps were found in LT-GaAs layers grown at 200°C and containing As clusters 6–8 nm in diameter. The activation energy of thermal electron emission from these traps was 0.47 and 0.59 eV, and their concentration was ∼10¹⁷ cm⁻³, which is comparable with the concentration of As clusters determined by transmission electron microscopy. In LT-GaAs samples that were grown at 300°C and contained no arsenic clusters, the activation energy of traps was 0.61 eV. The interrelation between these electron levels and the system of As clusters and point defects in LT-GaAs is discussed. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 4, 2004, pp. 401–406. Original Russian Text Copyright ? 2004 by Brunkov, Gutkin, Moiseenko, Musikhin, Chaldyshev, Cherkashin, Konnikov, Preobrazhenskii, Putyato, Semyagin.     

Semi-insulating GaN:C epilayers grown by metalorganic vapor phase epitaxy using propane as a carbon source

The influence of propane present in a reactor at various stages of GaN growth by metalorganic vapor phase epitaxy (MOVPE) on sapphire substrates on the character of epitaxial process and the properties of epilayers has been studied. Doped GaN epilayers with carbon concentration 5 × 10¹⁸ cm^–3 characterized by high crystalline perfection, an atomically smooth surface, and electric breakdown voltage above 500 V at a doped layer thickness of 4 μm have been obtained.

     

Capacitance studies of multilayer ensembles of InAs QDs in a GaAs matrix

Quasi-static capacitance characteristics of multilayer arrays of vertically coupled InAs quantum dots (QDs) in a GaAs matrix were analyzed on the assumption of a Gaussian energy distribution of the ground state of the QDs. An array of InAs QDs with a characteristic base size of about 20 nm and height of ～3 nm was ordered in the growth direction and had 3, 6, or 10 layers spaced by ～5 nm. It was found that, as the number of layers increases from 3 to 10, the average binding energy of the ground electron state grows from ～80 to ～120 meV and the root mean square deviation characterizing the energy distribution of the levels of this state decreases from ～30 to ～15 meV.     

Dependence of the efficiency of III-N blue LEDs on the structural perfection of GaN epitaxial buffer layers

III-N blue LED structures with active regions based on InGaN nanoislands are studied. The structures are grown by metalorganic vapor-phase epitaxy (MOVPE) on GaN layers deposited by various methods for the initial formation of an epitaxial layer. It is shown that, due to strong carrier localization in narrow-gap InGaN nanoislands, the electroluminescence efficiency is independent of the crystal perfection of the material.     

Study of the electrical properties of individual (Ga,Mn)As nanowires

Arrays of (Ga, Mn)As nanowire crystals are synthesized by molecular-beam epitaxy. Electronbeam lithography made possible the fabrication of electric contacts to individual nanowires. The influence of the annealing temperature on the properties of the contacts is studied. The optical annealing temperature is determined to be 160°C. It is found that an increase in the annealing temperature yields structure degradation. From studies of the current-voltage characteristics of the individual nanowire structures, a number of their electrical parameters, such as the resistivity and the mobility of charge carriers are determined.