The nucleation of HCl and Cl₂‐based HVPE GaN on mis‐oriented sapphire substrates

Abstract

The nucleation of both classic HCl‐based and novel Cl 2 ‐ based HVPE GaN on mis‐oriented sapphire substrates was investigated. The use of Cl2in HVPE increases the growth rate by a factor of 4‐5 and strongly reduces the parasitic deposition, allowing for the growth of much thicker wafers than HCl‐based HVPE. Morphological SEM surface studies of the HCl‐based HVPE sample surface show that at 600 °C a nanocrystalline layer is deposited on the sapphire. During the subsequent annealing phase, the morphology changes to a μm‐sized island structure. During overgrowth at 1080 °C, the islands coalesce. Small voids or pinholes are then formed in between the coalescing GaN islands. These pinholes lead to numerous pits on the surface of the GaN at thicknesses of 5 μm. The pits disappear during continued overgrowth and can no longer be found on the surface, when the GaN film reaches a thickness of 45 μm. This particular coalescence mechanism also applies to Cl2‐based HVPE GaN on sapphire (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Vertical gallium nitride schottky diodes for power switching applications.

“…substrate. However, films grown using HVPE technique suffer from higher threading dislocation density (TDD) on the order of 10 9 cm -2 when grown on heterosubstrates [18]. For instance, the lattice mismatch between GaN and substrates such as Si, SiC, and sapphire are reported to be 17%,3.3%, and 13%…”