Analysis of reactor geometry and diluent gas flow effects on the metalorganic vapor phase epitaxy of AlN and GaN thin films on α(6H)-SiC substrates

The influence of diluent gas on the metalorganic vapor phase epitaxy of AIN and GaN thin films has been investigated. A computational fluid dynamics model using the finite element method was employed to improve film uniformity and to analyze transport phenomena. The properties of AIN and GaN thin films grown on alpha(6H)-SiC(0001) substrates in H-2 and N-2 diluent gas environments were evaluated. Thin films of AIN grown in H-2 and N-2 had root mean square (rms) roughness values of 1.5 and 1.8 nm, respectively. The surface and defect microstructures of the GaN thin films, observed by scanning and transmission electron microscopy, respectively, were very similar for both diluents. Low temperature (12K) photoluminescence measurements of GaN films grown in N-2 had peak intensities and full widths at half maximum equal to or better than those films grown in H-2. A room temperature Hall mobility of 275 cm(2)/V.s was measured on 1 mu m thick, Si-doped, n-type (1 x 10(17) cm(-3)) GaN films grown in N-2. Acceptor-type behavior of Mg-doped GaN films deposited in N-2 was repeatably obtained without post-growth annealing, in contrast to similar films grown in H-2. The GaN growth rates were similar to 30% higher when H-2 was used as the diluent. The measured differences in the growth rates of AIN and GaN films in H-2 and N-2 was attributed to the different transport properties of these mixtures, and agreed well with the computer model predictions. Nitrogen is shown to be a feasible alternative diluent to hydrogen for the growth of AIN and GaN thin films.