Near Defect Free GaN Substrates

Abstract

The current status of GaN crystallization under high nitrogen pressure will be presented. Both conductive and semi-insulating GaN crystals will be characterized.In particular the influence of Mg on the growth mechanisms will be discussed. The influence of Mg doping on morphology of Mg-doped crystals grown under pressure and Mg-doped homoepitaxial layers will be shown. It will be also shown that the addition of about 1 at.% of Mg into the solution improves significantly the structural quality of crystals reducing dislocation density at least by 3 orders of magnitude comparing to the crystals grown without an intentional doping. As it was estimated by selective wet etching and transmission electron microscopy the dislocation densities in the Mg-doped GaN is as low as 10 cm−1. The introduction of Mg also lowers the optical absorption coefficients for energies below fundamental edge by 2 to 3 orders of magnitude what is explained by disappearance of defect related states in the gap.The procedures for preparation of atomically flat epi-ready (000 1 ) surfaces without subsurface damage will be described. It will be shown that high quality homoepitaxial layers growing by monoatomic steps are possible on these substrates.

Ammonothermal Bulk GaN Growth and Its Processing

“…Several approaches to grow bulk GaN crystals from solutions in closed reactors have been reported, e.g., high-pressure solution growth, (4,5) low-pressure solution growth with flux (6,7) and ammonothermal growth. (8)(9)(10) Despite the advantage of scalability over its counterparts, not many research institutes have attempted ammonothermal growth because the growth rate is relatively low, and high-pressure ammonothermal reactors are not commercially available.…”

High electron mobility in AlGaN/GaN heterostructures grown on bulk GaN substrates

“…These crystals were tested to be semi-insulating with a perfect crystallographic structure. 7 Prior to growth, the ͑0001͒ Ga face, which was found to be the best face polarity for a homoepitaxial layer, 8 as the nitrogen precursor and the group-III element were provided by standard solid-source effusion cells. An unintentionally doped GaN layer of about 1 m was grown at 800°C on a Mg-doped GaN single crystal, followed by a 200-Å-thick AlGaN layer.…”

GaN–AlGaN heterostructure field-effect transistors over bulk GaN substrates

“…6,7 This leads to photoluminescence spectra with very well-resolved excitonic transition lines of widths below 1 meV. 8 Recently, Mg-doped high-pressure-grown bulk GaN crystals were shown to be semi-insulating with perfect crystallographic structure.…”