Strain relief and its effect on the properties of GaN using isoelectronic In doping grown by metalorganic vapor phase epitaxy

We studied the effect of isoelectronic In doping on the crystalline and optical properties of GaN grown on sapphire with H-2 or N-2 carrier gas by metalorganic vapor phase epitaxy. The relationship between lattice constants c and a obtained by x-ray diffraction analysis showed that with increasing trimethylindium (TMI) flow during growth, the strain in GaN decreased, and accordingly, the tilting and the twisting components of crystalline mosaicity also decreased. In addition, the Raman shift, the excitonic photoluminescence peak energy, and the its linewidth shifted in accordance with the magnitude and the sign of the strain in GaN, regardless of the carrier gas used. These results revealed that for a smaller TMI flow region, In was incorporated so that the crystallinity of GaN improved, and for a larger TMI flow region, In substituted for Ga so that alloying formation might have occurred. (C) 1999 American Institute of Physics. [S0003-6951(99)04452-6].