Morphology evolution of homoepitaxial growth of aluminum nitride by hydride vapor phase epitaxy

Free-standing aluminum nitride (AlN) crystals prepared by physical vapor transport (PVT) have been utilized as substrates for the homoepitaxial growth of AlN thick layers by using hydride vapor phase epitaxy (HVPE). The morphology evolution has been investigated in details under various growth conditions. The surface conditions from step flow to step bunching growth mode are governed by growth rates and V/III ratios, which is attributed to the vapor supersaturation. The presence of microcrystal inclusions, formation of spiral hillocks and occurrence of cracks could cause severe surface degradation. Additionally, the substrate misorientation also contributes to the morphology variation to some extent. By optimizing key growth parameters, a 300-mu m thick homoepitaxial AlN layer with a smooth surface and high deep UV transparency has been successfully prepared by HVPE method.