Electronic and structural properties of GaN grown by hydride vapor phase epitaxy

The electronic and structural properties of GaN were investigated for heteroepitaxial layers grown by hydride vapor phase epitaxy. Uniform film nucleation on the sapphire substrates was facilitated by a GaCl pretreatment. The films were all unintentionally doped n type. Variable temperature Hall effect measurements reveal electron concentrations as low as 2×1017 cm−3 and electron mobilities as high as 460 cm2/V s at 300 K. The films exhibit bound exciton photoluminescence lines with a full width at half-maximum (FWHM) of 2.42 meV at 2 K. Transmission electron microscopy studies of the GaN/sapphire interface reveal a ∼200 nm thick, highly defective GaN layer consisting predominantly of stacking faults. The excellent quality of these GaN films is attributed to this ‘‘auto-buffer’’ layer which enables growth of GaN cells with a dislocation density of ∼3×108 cm−2 after ∼12 μm of film growth.