Development of GaN wafers for solid-state lighting via the ammonothermal method

Abstract

In order for solid-state lighting to replace existing light bulbs, high power LEDs will be required to handle more current than conventional LEDs. When current densities in high power LEDs become comparable to that of Laser Diodes (LDs), GaN substrates will be critically useful for device reliability. Due to its significant scalability, the ammonothermal growth of bulk GaN could provide cost competitive wafers for high power LEDs.Our team has focused on developing the basic ammonothermal growth method in small 1” internal diameter prototype autoclaves capable of accommodating multiple crystals simultaneously. We have made considerable improvements in the crystal quality particularly in transparency and structural parameters. By optimizing the growth process we have improved the coloration and transparency of the crystals from a black/brown to semi-transparent yellow. We have improved the absorption coefficient at 450nm from 30.5cm−1 to 8cm−1 yielding semi-transparent crystals. Currently, we can reliably achieve a full width half maximum (FWHM) of X-ray 002 reflection between 100 and 300arcs. The crystals have a low dislocation density less than 10−6cm−2 and are n-type with a resistivity of approximately ρ∼10−2Ωcm. In this presentation we will discuss improvements that we have made to provide a more suitable substrate for future high power LEDs.