Plasma-assisted MBE of GaN pn-junction Grown on Si(111) Substrate

We investigated growth of GaN pn-junction layers grown on silicon(111) by plasma-assisted molecular beam epitaxy system and its application for photo-devices. Si and Mg were used as n- and p-dopants, respectively. The reflection high energy electron diffraction images indicated a good surface morphology of GaN pn-junction layer. The thickness of GaN pn-junctions layers was about 0.705 nm. The absence of cubic phase GaN showed that this layer possessed hexagonal structure. According to XRD symmetric rocking curve ω/2θ scans of (0002) plane at room temperature, the full width at half-maximun of GaN pn-junction sample was calculated as 0.34o, indicating a high quality layer of GaN pn-junction. Surprisingly, there was no quenching of the A1(LO) peak, with the presence of Si- and Mg-dopants in sample. The pn-junctions sample has a good optical quality which was measured by thephotoluminescence system. For photo-devices applications, Ni and Al were used as front and back contacts, respectively. The current-voltage characteristics of the devices showed the typical rectifying behavior of heterojunction. The photo-current measurement was performed using a visible-lamp under forward and reverse biases. From the temperature-dependent measurements, the current at low bias exhibited much stronger temperature dependence and weaker field dependence. The effect of thermal annealing on front contact Ni was also carried out. The front contact Ni was annealed at 400 and 600 oC for 10 min in the nitrogen ambient. The results showed that 600 oC treated sample had a higher gain at 1.00 V/e than 400 oC treated and untreated samples.