Novel growth methods of III-nitrides on 6hydrogen-silicon carbide(0001)

The objectives of the research described herein were to determine the effect of process parameters on the physical and chemical characteristics of GaN thin films, GaN overgrowth layers and AlGaN/GaN heterostructures grown via metalorganic vapor phase epitaxy on 6H-SiC(0001) substrates. The relationships among growth temperature, the flow rates of the reactant species and the V(NH ₃)/III(tri-ethylgallium) gas ratios with growth and decomposition rates along [0001] and [1120] were determined for pendeo-epitaxial (PE) growth of GaN overlayers. Decomposition of the GaN(0001) surface was observed above 1060°C, but no decomposition of the (1120) sidewalls was indicated up to 1100°C. The lateral [1120]-to-vertical [0001] growth rate ratio and the rate of coalescence between the laterally growing “wings” of PE GaN were enhanced by (1) increasing the temperature, which increased the growth rate along [1120] and the decomposition rate from the (0001) surface and (2) decreasing the flow rate of the tri-ethylgallium which decreased the growth rate along [0001].; Temperature was also important in controlling the roughness of the GaN(0001) surface. An optimum temperature of 1020°C was determined, below which the GaN islands formed in the initial stages of growth on the AIN buffer layers did not coalesce properly and above which nucleation of hillocks on heterogeneous steps formed at the intersection of dislocations with the growth surface was pervasive. A hillock density of 106 cm−2 was measured on the surfaces of GaN thin films and on the stripes of the PE films having a density of threading dislocations of 109 cm −2, while no spiral hillock formation was observed on the PE wing material having a dislocation density of 105 cm −2 as measured by TEM, AFM and XRD. The achievement of intentional acceptor-type doping of III-N materials was accomplished through the use of Mg-doped AlGaN/GaN heterostructures. The sheet conductance of the GaN/AlGaN heterostructure was higher due to piezoelectric acceptor doping and modulation doping effects in addition to conventional Mg acceptor doping.