  Ammonia (NH3) is commonly used as group V precursor in gallium nitride (GaN)
metalorganic chemical vapor deposition (MOCVD). The high background carbon (C)
impurity in MOCVD GaN is related to the low pyrolysis efficiency of NH3, which
represents one of the fundamental challenges hindering the development of high
purity thick GaN for vertical high power device applications. This work uses a
laser-assisted MOCVD (LA-MOCVD) growth technique to address the high-C issue in
MOCVD GaN. Carbon dioxide (CO2) laser with wavelength of 9.219 um was utilized
to facilitate NH3 decomposition via resonant vibrational excitation. The
LA-MOCVD GaN growth rate (as high as 10 um/hr) shows a strong linear
relationship with the trimethylgallium (TMGa) flow rate, indicating high
effective V/III ratios and hence efficient NH3 decomposition. Pits-free surface
morphology of LA-MOCVD GaN was demonstrated for films with growth rate as high
as 8.5 um/hr. The background [C] in LA-MOCVD GaN films decreases monotonically
as the laser power increases. A low [C] at 5.5E15 cm-3 was achieved in LA-MOCVD
GaN film grown with the growth rate of 4 um/hr. Charge transport
characterization of LA-MOCVD GaN films reveals high crystalline quality with
room temperature mobility >1000 cm2/Vs. LA-MOCVD growth technique provides an
enabling route to achieve high quality GaN epitaxy with low-C impurity and fast
growth rate simultaneously. This technique can also be extended for epitaxy of
other nitride-based semiconductors.
