Homo-epitaxial growth of n-GaN layers free from carbon-induced mobility collapse and off-angle-dependent doping variation by quartz-free hydride vapor phase epitaxy

Abstract

Certain undesired phenomena are observed in n-GaN layers grown by metal–organic chemical vapor deposition (MOCVD) due to the unavoidable C-induced carrier compensation. They are a drastic reduction in carrier mobility, called mobility collapse, and significant non-uniformity in the carrier concentration due to the off-angle dependence of the C-incorporation efficiency of the process. These phenomena are particularly severe for low doping levels between 1015 and 1016/cm3, which are suitable for fabricating drift layers used in vertical-type GaN power devices that operate in the range of a few kilovolts to tens of kilovolts. However, the C-related undesired characteristics are absent in homo-epitaxial n-GaN layers grown by quartz-free hydride vapor phase epitaxy (QF-HVPE), recently developed by us. The utilization of C-free raw materials alongside quartz-free parts enables the growth of highly pure GaN crystals with negligible Si, C, and O incorporations. These crystals exhibited an electron concentration in the low-1015/cm3 range with the highest reported room temperature electron mobility, μ, of 1470 cm2/V s among GaN crystals, whereas n-GaN layers with similar carrier concentrations but containing C-compensation, as in the case of those grown by MOCVD, exhibited a severe mobility collapse (μ = 288 cm2/V s). High uniformity in the carrier concentration with a small standard deviation of 4.0% was observed in a 2-in. n-GaN wafer grown by QF-HVPE on a GaN substrate with an off-angle variation of 0.3°. On the other hand, the standard deviation of the carrier concentration in wafers grown by MOCVD was approximately 17% because of the off-angle-dependent C-incorporation.