Bulk GaN crystals grown at high pressure as substrates for blue-laser technology

Abstract

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)