Structural characterization of nonpolar (112̄0) a-plane GaN thin films grown on (11̄02) r-plane sapphire

Abstract

In this letter we describe the structural characteristics of nonpolar $\text{(112̄0)}$ a-plane GaN thin films grown on $\text{(11̄02)}$ r-plane sapphire substrates via metalorganic chemical vapor deposition. Planar growth surfaces have been achieved and the potential for device-quality layers realized by depositing a low temperature nucleation layer prior to high temperature epitaxial growth. The in-plane orientation of the GaN with respect to the $r$ -plane sapphire substrate was confirmed to be ${\text{[0001]}}_{\mathrm{GaN}}{\text{‖[1̄101]}}_{\mathrm{sapphire}}$ and ${\text{[1̄100]}}_{\mathrm{GaN}}{\text{‖[112̄0]}}_{\mathrm{sapphire}}.$ This relationship is explicitly defined since the polarity of the $a$ -GaN films was determined using convergent beam electron diffraction. Threading dislocations and stacking faults, observed in plan-view and cross-sectional transmission electron microscope images, dominated the $a$ -GaN microstructure with densities of ${\text{2.6×10}}^{10}\hspace{0.17em}{\mathrm{cm}}^{\text{−2}}$ and ${\text{3.8×10}}^5\hspace{0.17em}{\mathrm{cm}}^{\text{−1}},$ respectively. Submicron pits and crystallographic terraces were observed on the optically specular $a$ -GaN surface with atomic force microscopy.