Laser-induced reactive epitaxy of binary and ternary group III nitride heterostructures

Group III nitride films are deposited on sapphire (0 0 0 1) substrates using the laser-induced reactive epitaxy (LIRE) method. Liquid group III metal targets are ablated by a focused nanosecond Nd:YAG laser beam in a nitrogen atmosphere of 0.1 mbar. In the plasma plume, the molecular nitrogen is cracked to atomic nitrogen. The cracking process is investigated by optical plasma spectroscopy. By varying the laser pulse energy, the III/V ratio can be controlled. The investigated heterostructures consist of a AlGaN buffer layer, a low temperature (LT) GaN layer and finally a GaN epilayer. By optimising the III/V ratio and the growth temperature of both LT-GaN buffer and epilayer, the luminescent and electronic properties are strongly enhanced. As best results, we achieved residual carrier concentrations of 2×1017 cm−3 and mobilities of 70 cm2/Vs. The FWHM value for the near band-edge luminescence was 76 meV and for the rocking curve at the (0 0 0 2) reflex it was 720 arcsec. InN and InGaN films with In contents up to 13% are grown using molten In and InGa alloy as target materials. The InN films commonly have high electron mobilities. We found values up to 350 cm2/Vs. For the Mg-doping of GaN, a liquid GaMg alloy is used. The results show that we are able to incorporate the required amount of Mg into the nitride.