Structure of nonpolar gallium nitride films grown by hydride vapor phase epitaxy.

摘要

Conventional c-plane (Al, In, Ga)N optoelectronic devices suffer from deleterious polarization effects. These polarization effects can be eliminated by growing devices on alternative orientations of GaN crystals, such as {lcub}11¯00{rcub} m-plane or {lcub}112¯0{rcub} a-plane films. Previous attempts to grow nonpolar GaN by HVPE, yielded rough and faceted surfaces that were unsuitable for substrate use.; This dissertation describes the structural and morphological characteristics of planar, nonpolar GaN films grown by hydride vapor phase epitaxy (HVPE). Smooth, specular a-plane GaN films were grown on r-plane sapphire substrates. While smooth enough to allow device fabrication on them, these films contained ∼1010 cm -2 dislocations and ∼105 cm-1 basal plane stacking faults. Lateral epitaxial overgrowth was developed to eliminate dislocations and stacking faults in the overgrown material, reducing local dislocation and fault densities below 5 x 106 cm -2 and 5 x 103 cm-1, respectively. Significant improvements in surface morphology and luminescence characteristics of the films resulted from the structural defect elimination. Threading dislocations were shown to be responsible for the surface morphological instability that has previously complicated the growth of planar a-plane GaN by HYPE, MBE, and MOCVD.; This dissertation further describes planar m-plane GaN films and free-standing wafers that have now been produced by HVPE. Free-standing 48 mm diameter m-plane GaN wafers were grown directly on (100) gamma-LiAlO2 substrates. These wafers were largely free of bulk defects that had previously plagued m-plane GaN films grown by HVPE. Just as with their a-plane counterparts, these m-plane GaN films contained high threading dislocation and stacking fault densities. LEO of m-plane GaN films was demonstrated and found effective for reducing extended defect densities in the films. Elimination of stacking faults from the overgrown material showed that the commonly observed "slate" surface morphology is a manifestation of faulting in the crystal. Fault-free m-plane GaN exhibits step-flow-like surfaces with RMS roughness of ∼0.6 nm. In summary, smooth, high-quality a- and m-plane GaN templates can now be grown by HVPE for use in the fabrication of nonpolar nitride devices.