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
Abstract:
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.