A. Khachapuridze

Spin Selection Rules in Radiative and Nonradiative Recombination Processes in Bulk Crystals and in Thin Films of II–VI Compounds

The origin of a fast component of Mn 2+ intra-shell photoluminescence (PL) decay is discussed. We demonstrate that efficient spin-dependent interactions between localised spins of Mn ions and spins of free carriers result in a variation of formation and decay rates of PL emissions in diluted magnetic semiconductors and affect spin selection rules for radiative recombination transitions.

Hole carrier concentration and photoluminescence in magnesium doped InGaN and GaN grown on sapphire and GaN misoriented substrates

Systematic studies of InxGa1−xN layers (0≤x<0.13) doped with Mg were performed. Samples were grown by metal organic vapor phase epitaxy. Intermediate Mg doping in the range of 2×1019 cm−3 was chosen to achieve a maximum hole carrier concentration, pH (as measured by Hall effect) of 4×1018 cm−3 in samples with high x. We confirmed reports on decreasing resistivity in InxGa1−xN:Mg epitaxial layers observed with increasing x. This finding is very important for applications. In the performed research we attempted to separate contributions to pH increase resulting from increase in In-content and an associated decrease in growth temperature, Tgr (necessary to obtain high x). For this purpose In-content increase was achieved by means of either (i) lowering the growth temperature (from 1020 to 830 °C) or by (ii) varying an intended GaN substrate miscut. We demonstrated that the increase in pH in InxGa1−xN:Mg is caused by higher In concentration while a drop in Tgr plays a secondary role. Studies of photoluminesce...

Carrier recombination mechanisms in nitride single quantum well light-emitting diodes revealed by photo- and electroluminescence

Light emission of nitride single quantum well light-emitting diodes operating in the range from 395 to 440 nm, grown by metal-organic vapor phase epitaxy, was investigated by means of photoluminescence (PL) and electroluminescence (EL) spectroscopies as functions of temperature and current injection level. The indium content of the active layers was varied via the growth temperature, which ranged from 770 to 810 °C. It was found that samples with higher indium contents (grown at lower temperatures) exhibit larger luminescence full widths at half maximum (FWHMs) and higher EL intensities. The larger FWHM points to a larger amplitude of the potential profile fluctuations, which suggests that these fluctuations may be useful for the increase in the device output power. In agreement with this result, the performed examination by PL measurements shows large thermal stability of the luminescence intensity for the lowest growth temperature sample. On the other hand, a nontrivial dependence of thermal stability o...

Interplay of stimulated emission and Auger‐like effect in violet and blue InGaN laser diodes

We have studied two types of InGaN laser diodes emitting at 410 and 440 nm, looking for the presence of the efficiency “droop” and its influence on the performance of these devices. By measuring the devices in two experimental geometries: a) along the resonator axis, b) perpendicularly to the cavity, we were able to conclude that the light emission process in these laser diodes operating below the threshold are governed by two mechanisms: Auger-like effect and the stimulated recombination. The competition of these two mechanisms leads to the suppression of the droop if the light is observed along the axis of the cavity. The relatively low onset of the stimulated recombination may account for the robustness of these devices against the nonradiative process (Auger-like recombination) appearing at high current densities. Additionally, we performed the characterization of InGaN light emitting diodes grown on substrates with varied In content and defect density. The results clearly demonstrate that the droop is not related in any way with the above mentioned parameters at least in the dislocation density range between 105 and 109 cm-2 and In composition range between 0.1-0.15. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)