Microstructural, optical, and electrical characterization of semipolar (1122) gallium nitride grown by epitaxial lateral overgrowth

摘要

Semipolar (1122) gallium nitride (GaN) films have been grown on m-plane (1100) sapphire by epitaxial lateral overgrowth. Transmission electron microscopy (TEM) studies show that the inclination of the [0001] axis at 32° from the film surface combined with the high [0001] growth rate under the reactor conditions used, allowed a low defect density (LDD) wing growing along [0001] to partially overgrow the highly defective window region and the other wing, resulting in a coalescence boundary, at which stacking faults and dislocations appear to terminate. Low temperature cathodoluminescence (CL) was performed to correlate the optical properties with the different stages of the growth process. It is found that emission from the LDD wing is dominated by near band edge recombination, whereas an emission band at 3.42 eV related to basal plane stacking faults and a broad band from 3.15-3.38 eV possibly related to emission from prismatic stacking faults and partial dislocations were observed in the window region. Scanning capacitance microscopy (SCM) studies showed that almost the entire film is unintentionally n-doped. By correlating the spatial variation in the unintentional doping to the overgrowth process, different impurity incorporation rates between the (1122) and (0001) facets have been observed. Dislocations of a or a + c type were found to bend over toward the growth direction in the LDD wing by TEM appear to be nonradiative by cross-sectional CL and SCM studies have revealed that they also impact the local electrical properties.