Si-implantation activation annealing of GaN up to 1400°C

Implant activation annealing of Si-implanted GaN is reported for temperatures from 1100 to 1400°C. Free electron concentrations up to 3.5 × 10²⁰ cm^-3 are estimated at the peak of the implanted profile with Hall mobilities of ∼60 cm²V/s for annealing at 1300°C for 30 s with an AlN encapsulant layer. This mobility is comparable to epitaxial GaN doped at a similarly high level. For annealing at >1300°C, the sample must be encapsulated with AlN to prevent decomposition of the GaN layer. Channeling Rutherford backscattering demonstrates the partial removal of the implant damage after a 1400°C anneal with a minimum channeling yield of 12.6% compared to 38.6% for the as-implanted spectrum. Scanning electron microscope images show evidence of decomposition of unencapsulated GaN after a 1300°C anneal and complete sublimation after 1400°C. The use of AlN encapsulation and annealing at temperatures of ~∼300°C will allow the formation of selective areas of highly doped GaN to reduce the contact and access resistance in GaN-based transistors and thyristors.