Metalorganic chemical vapor deposition of gallium nitride on silicon carbide for high electron mobility transistors.

摘要

AlGaN/GaN HEMT devices represent a potentially breakthrough technology for various applications in wireless communication infrastructure and high power switches. Heteroepitaxial devices fabricated on sapphire had previously shown high performance promise, yet were limited primarily by self-heating effects due to the poor thermal conductivity (kappa ∼ 0.42 W/cm·K at 300 K) of the substrate. This work investigates GaN epitaxial growth using MOCVD on SiC (kappa ∼ 3.4 W/cm·K at 300 K) as primary substrate for nitride based electronics.; Interrupted growths of AlN and GaN establish that these films grow via an island coalescence mechanism. Cross sectional transmission electron microscopy (TEM) reveals that these islands are free of threading dislocations prior to coalescence. The GaN islands are found to be relaxed throughout the entire growth process resulting in a true Volmer-Weber growth mode. Detailed TEM imaging reveals a network of misfit dislocations at the AlN/GaN interface, providing the mechanism for the lattice mismatch relaxation. A simple, low angle grain boundary model based on island misorientation at coalescence provides reasonable agreement with TD densities measured using plan view TEM and AFM, confirming the source of dislocation generation. Optimized GaN material had a threading dislocation density of ∼2 x 10 8/cm2 and an electron mobility of ∼818 cm 2/V·s.; Reducing the reactor pressure to 76 Torr during growth produced highly resistive GaN. This material was shown to have a high background concentration of carbon, however, deep level optical spectroscopy additionally revealed the presence of additional significant concentrations of trap levels at E c-2.7 eV and Ec-1.35 eV.; HEMT devices fabricated using a highly resistive buffer and optimized device layout had a record breakdown of >1300 V. Devices fabricated on material optimized for structural properties had a maximum microwave output power of >8.4 W/mm. A novel HEMT structure combining both of these material characteristics was developed and evaluated for both power switching and microwave amplifier applications.