Growth of gallium nitride on porous silicon carbide substrates.

摘要

Gallium Nitride (GaN) is a wide band gap compound semiconductor. One of the major challenges associated with the growth of GaN crystals is to find a suitable substrate for epitaxial overgrowth of GaN in order to reduce the dislocation density in the film. The use of porous substrates has recently been suggested as an potential solution to this problem. It has been proposed that the porous substrates can lead to defect reduction in the GaN film due to dislocation annihilation and lateral epitaxial overgrowth. The purpose of this thesis is to study the effect of porous substrates for dislocation reduction in the GaN films. We have studied various mechanisms of GaN film growth on porous substrates, primarily porous SiC, and examined how they can lead to dislocation density reduction in the film.; The morphology of the porous network in porous SiC has been studied in detail. The hydrogen etching rates of porous and nonporous SiC have also been measured. Etch rates of porous and nonporous wafers of various miscuts are found to be equal within a factor of two, indicating that the rate-limiting step in the etching process arises from the supply of active etching species from the gas phase. The porous SiC etches slightly faster than the nonporous SiC, which is interpreted simply in terms of the reduced average density of the porous material.; The porous SiC substrates are characterized in terms of their porosity and pore size by using x-ray reflectivity and diffuse x-ray scattering. X-ray reflectivity gives information about the surface porosity of the porous SiC samples. A model has been developed to interpret the diffuse x-ray scattering data from a porous SiC sample in order to measure the average pore size and bulk porosity.; The GaN films on porous SiC were grown by plasma assisted molecular beam epitaxy (PAMBE). We have studied MBE growth of GaN on porous SiC substrates. The effect of the porous SiC substrate on the dislocations and strain in the GaN overgrown film is studied in detail, using various characterization tools including x-ray diffraction, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). TEM images show that the GaN film grown on porous substrates contains open tubes and a low dislocation density in regions between tubes. (Abstract shortened by UMI.)