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.

Metalorganic Chemical Vapor Deposition Gallium Nitride with Fast Growth Rate for Vertical Power Device Applications

“…However, as shown in Figure 1a, although N d – N a is parallel to [Si] above 1 × 10 16 cm −3 , it showed a faster decrease as the SiH 4 flow rate reduces below 1 × 10 16 cm −3 . This phenomenon has been observed in previous studies on MOCVD GaN [ 36–40 ] when N d – N a is below mid‐ to low‐10 16 cm −3 . In this work, a low N d – N a at 4 × 10 15 cm −3 was achieved with a SiH 4 flow rate of 1.4 pmol min −1 , which is among one of the lowest intentional doping concentrations reported in the literature, [ 7,22,36–42 ] as shown in Figure 1b.…”

Space–Charge Profiles and Carrier Transport Properties in Dopant‐Free GaN‐Based p‐n Junction Formed by Distributed Polarization Doping

“…Gallium nitride (GaN) has been in the spotlight as a material for high-power devices thanks to its high critical electric field (%3 MV cm À1 ) and high electron mobility (%1500 cm 2 V À1 s À1 ). [1][2][3][4] The p-n junction is an essential component for power devices with high breakdown voltage and low on-resistance; however, Mg atoms used for p-type doping cause various issues from the viewpoints of both production and device characteristics. For instance, surface segregation, diffusion, and memory effects of Mg atoms make the precise control of the doping profile difficult.…”

Substitutional diffusion of Mg into GaN from GaN/Mg mixture

“…allium nitride (GaN) is one of the most promising materials for high-power devices owing to its excellent physical properties such as high breakdown field and high saturated electron velocity. [1][2][3] It has already been commercialized for lateral devices such as highelectron-mobility transistors, which are expected to become increasingly popular. On the other hand, the technique of fabricating vertical power devices has not been as wellestablished as that of fabricating lateral ones because there are still many unresolved issues specific to GaN.…”