Substantial and simultaneous reduction of major electron traps and residual carbon in homoepitaxial GaN layers

Abstract

The presence of large amounts of electron traps together with residual carbon, as well as their trade-off relationship, is an obstacle to fabricating next-generation GaN-based power devices using the metal-organic chemical vapor deposition (MOCVD) method. Using the hydride vapor phase epitaxy (HVPE) method, we have overcome all of the aforementioned obstacles. In a previous study, we realized GaN homoepitaxial layers with greater purity than the best MOCVD-grown layers by removing quartz components from the high-temperature region of the HVPE apparatus. In the present study, the concentration of residual carbon was further reduced to less than 3 × 1014 cm-3 by removing carbon components near the wafer. In addition, the concentrations of major electron traps widely observed in homoepitaxial GaN layers were substantially reduced to the 1012-1013 cm-3 range via further modification of the HVPE conditions/apparatus to suppress etching of a stainless-steel flange of the HVPE reactor. The results imply that stainless-steel-related impurities such as Fe and Cr are the most likely cause of the major electron traps although native point defects have long been considered their origin. The resultant GaN layers, which showed substantially improved optical and electrical properties, did not exhibit a trade-off relationship between the concentrations of carbon and electron traps.