Enhanced growth rates and reduced parasitic deposition by the substitution of Cl-2 for HCl in GaN HVPE
Bohnen T (Bohnen, Tim)1, Ashraf H (Ashraf, Hina)1, van Dreumel GWG (van Dreumel, Gerbe W. G.)1, Verhagen S (Verhagen, Sjoerd)1, Weyher JL (Weyher, Jan L.)1, Hageman PR (Hageman, Paul R.)1, Vlieg E (Vlieg, Elias)1
J. of Crys. Growth Volume: 312    Issue: 18    Pages: 2542-2550

The main limitation in the application of hydride vapor phase epitaxy for the large scale production of thick free-standing GaN substrates is the so-called parasitic deposition, which limits the growth time and wafer thickness by blocking the gallium precursor inlet. By utilizing Cl-2 instead of the usual HCl gas for the production of the gallium chlorine precursor, we found a rapid increase in growth rate from similar to 80 to similar to 400 mu m/h for an equally large flow of 25 sccm. This allowed us to grow, without any additional optimization, 1.2 mm thick high quality GaN wafers, which spontaneously lifted off from their 0.3 degrees mis-oriented GaN on sapphire HCl-based HVPE templates. These layers exhibited clear transparencies, indicating a high purity, dislocation densities in the order of 10(6) cm(-2), and narrow rocking curve XRD FWHMs of 54 and 166 arcsec in for the 0002 and 101-5 directions, respectively.

In view of these findings, the possibility of depositing Cl-2-based HVPE GaN directly on sapphire via the standard low temperature nucleation-high temperature overgrowth process of classic HCl-based HVPE was investigated. By varying the Cl-2 flow during the 3 min long 615 degrees C nucleation phase, the nucleation conditions yielding smooth 0.7 similar to mm thick GaN on sapphire films were determined. The nucleation and coalescence mechanism of Cl-2-based HVPE GaN was found to proceed similar to that of HCl-based HVPE.