The effect of dislocations on the electrical characteristics of GaN p-n junctions has been examined through current–voltage measurements. Lateral epitaxial overgrowth (LEO) was used to produce areas of low dislocation density in close proximity to areas with the high dislocation density typical for growth on sapphire. A comparison of p-n diodes fabricated in each region reveals that reverse-bias leakage current is reduced by three orders of magnitude on LEO GaN. Temperature-dependent measurements on the LEO diodes indicate that the remaining leakage current in these devices is associated with a deep trap level.

This letter reports on the reduction in extended-defect densities in a-plane (112̄0) GaN films achieved via lateral epitaxial overgrowth (LEO) by hydride vapor phase-epitaxy. A variety of dielectric mask patterns was used to produce 8–125-μm-thick, fully coalesced nonpolar GaN films. The nanometer-scale pit densities in the overgrown regions were less than 3×106 cm−2 compared to ∼1010 cm−2 in the direct-growth a-plane GaN. Cathodoluminescence revealed a fourfold increase in luminous intensity in the overgrown material compared to the window material. X-ray rocking curves indicate the films were free of wing tilt within the sensitivity of the measurements. Whereas non-LEO a-plane GaN exhibits basal plane stacking fault and threading dislocation densities of 105 cm−1 and 109 cm−2, respectively, the overgrown LEO material was essentially free of extended defects. The basal plane stacking fault and threading dislocation densities in the wing regions were below the detection limits of ∼5×106 cm−2 and 3×103 cm−1, respectively.

Epitaxial growth and properties of III-V magnetic semiconductor (GaMn)As and its heterostructures

The structure and morphology of low growth temperature GaN nucleation layers have been studied using atomic force microscopy (AFM), reflection high energy electron diffraction (RHEED), and transmission electron microscopy (TEM). The nucleation layers were grown at 600 °C by atmospheric pressure metalorganic chemical vapor deposition (MOCVD) on c-plane sapphire. The layers consist of predominantly cubic GaN (c-GaN) with a high density of stacking faults and twins parallel to the film/substrate interface. The average grain size increases with increasing layer thickness and during the transition from low temperature (600 °C) to the high temperatures (1080 °C) necessary for the growth of device quality GaN. Upon heating to 1080 °C the nucleation layer partially converts to hexagonal GaN (h-GaN) while retaining a high stacking fault density. The mixed cubic-hexagonal character of the nucleation layer region is sustained after subsequent high-temperature GaN growth.