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Influence of growth conditions in plasma assisted molecular beam epitaxy on quality of GaN layers and GaN/AlGaN heterojunctions is studied. The growth diagram for step-flow growth mode and different nitrogen flux is presented. The low defect density of bulk GaN substrates together with very low impurity background concentrations resulted in high electron mobility for GaN/AlGaN heterojunctions: 109,000 cm2/Vs at 1.5 K, and 2500 cm2/Vs at 295 K. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

We employ cathodoluminescence (CL) technique for evaluation of in-depth and in-plane instabilities of light emission in laser diode structure. We study light emission properties from laser structure and their relation to microstructure details. Large in-plane instabilities of light emission are also present for excitation densities, larger than the threshold densities for the stimulated emission, i.e., potential fluctuations are not fully screened in the active region of the laser even at large excitation densities. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Compensation processes in magnesium doped GaN epilayers and bulk samples are studied. We demonstrate enhancement of potential fluctuations in Mg doped samples, from Kelvin probe atomic force microscopy measurements. Large- and small-scale light emission fluctuations are also demonstrated. Micro-photoluminescence (PL) study indicates an unusual anti-correlation between the intensities of excitonic and defect-related emission processes in p-type doped structures and also the presence of the so-called hot-PL. Hot-PL observed in compensated p-type samples, we relate to the presence of strong potential fluctuations. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

GaN single crystals exhibiting the lowest dislocation density (below 100/cm2) are grown at high hydrostatic N2 pressures of 10–20 kbar. Despite small dimensions of such crystals (up to 1/2") they offer a unique chance to construct high power laser diodes and some other devices. However, in order to develop high quality epitaxial structures, a number of steps, different to GaN epitaxy on foreign substrates, must be made. These steps include: (i) surface preparation of Ga-terminated side used for epitaxy, (ii) optimization of substrate thickness, (iii) optimization of substrate miscut, (iv) N-terminated side preparation for back-side contact. This work contains the following information: (i) description how the blue laser diodes on bulk GaN crystals are made, (ii) what is their crystallographic quality (in particular, a very large bowing for unrelaxed structures will be shown- the bowing radius can be as small as 0.1 m), (iii) what are the optical (very low threshold of 2.5 kW/cm2 for optical pumping) and (iv) electrical parameters (2.6 W (1.3 W per facet) optical power under pulsed operation). (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]