AlGaN materials for semiconductor sensors and emitters in 200- to 365-nm range

Abstract

In this paper we report on the fabrication and characterization of GaN, AlGaN, and AlN layers grown by hydride vapor phase epitaxy (HVPE). The layers were grown on 2-inch and 4-inch sapphire and 2-inch silicon carbide substrates. Thickness of the GaN layers was varied from 2 to 80 microns. Surface roughness, Rms, for the smoothest GaN layers was less than 0.5 nm, as measured by AFM using 10 μm x 10 μm scans. Background Nd-Na concentration for undoped GaN layers was less than 1x10 16 cm -3 . For n-type GaN layers doped with Si, concentration Nd-Na was controlled from 10 16 to 10 19 cm -3 . P-type GaN layers were fabricated using Mg doping with concentration Na-Nd ranging from 4x10 16 to 3x10 18 cm -3 , for various samples. Zn doping also resulted in p-type GaN formation with concnetration N D -N A in the 10 17 cm -3 range. UV transmission, photoluminescence, and crystal structure of AlGaN layers with AlN concentration up to 85 mole.% were studied. Dependence of optical band gap on AlGaN alloy composition was measured for the whole composition range. Thick (up to 75 microns) crack-free AlN layers were grown on SiC substrates. Etch pit density for such thick AlN layers was in the 10 7 cm -2 range.