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

摘要

GaN single crystals exhibiting the lowest dislocation density (below 100/cm~2) are grown at high hydrostatic N~2 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/cm~2 for optical pumping) and (ⅳ) electrical parameters (2.6 W (1.3 W per facet) optical power under pulsed operation).