In-doping to GaN and AlGaN was performed at 1000 degreesC by supplying trimethylindium (TMI). Concentrations of the In atoms in epitaxial layers were 10(18)similar to 10(19) cm(-3). GaN layers with and without the In-doping were characterized by molten KOH etching, photoluminescence (PL) and X-ray rocking curve (XRC) observations. Reduction of etch pit density by the In-doping was observed and narrowing of the full width at half maximum (FWHM) of PL and XRC spectra was also observed. These result indicate that dislocations in the growth layer are reduced. Narrowing of FWHM of XRC was also observed for AlGaN with the In-doping. Moreover, suppression of cracks on the AlGaN layer was observed by the In-doping. These results were attributed to relaxation of tensile stress in the AlGaN layer by the In-doping.