Electrical and optical properties of Si- and Mg-doped polycrystalline GaN on quartz glass substrate

High quality polycrystalline GaN layers are grown on quartz (silica) glass substrates by gas source molecular beam epitaxy using anion removed ECR (electron cyclotron resonance) radical cell. Unintentionally doped polycrystalline GaN layers grown at a substrate temperature of 770 degreesC show strong and narrow photoluminescence (PL) spectra and a high electrical resistivity. The n-type and p-type polycrystalline GaN layers are obtained by Si and Mg dopings, respectively. Carrier concentrations obtained are from 1.3 x 10(17) to 2.7 x 10(18) cm(-3) for n-type layers and 2.5 x 10(17) cm(-3) for p-type layers. With the increase in electron concentration, the full width at half maximum (FWHM) for 77 K PL spectra increases from 160 meV to 300 meV, and the PL peak shifts toward lower energy. The p-type layer shows a broad emission peaking at 3.17 eV, which is attributed to the free electron-hole transitions in Mg-doped GaN.