Hu Xiaobo

Progress in research of GaN-based LEDs fabricated on SiC substrate*

The influence of buffer layer growth conditions on the crystal quality and residual stress of GaN film grown on silicon carbide substrate is investigated. It is found that the AlGaN nucleation layer with high growth temperature can efficiently decrease the dislocation density and stress of the GaN film compared with AlN buffer layer. To increase the light extraction efficiency of GaN-based LEDs on SiC substrate, flip-chip structure and thin film flip-chip structure were designed and optimized. The fabricated blue LED had a maximum wall-plug efficiency of 72% at 80 mA. At 350 mA, the output power, the Vf, the dominant wavelength, and the wall-plug efficiency of the blue LED were 644 mW, 2.95 V, 460 nm, and 63%, respectively.

Theoretical investigation on surface kinetics of the SiC single crystal growth

According to the BCF theory, a simple surface diffusion model of SiC single crystal was established, and the key parameters such as the surface diffusion length, the critical nucleation and growth rate were obtained by theoretical calculation. The results show that surface diffusion length is 460nmat 2400K and it decreases with the rise of temperature. The relationship between the critical nucleation and the temperature was analyzed. For silicon surface, the critical saturation is decreased with the increase of temperature. Compared with silicon surface, the critical saturation of carbon surface is smaller and almost constant with the increase of temperature. That means, under the same saturation, two-dimensional nucleation occurs on the carbon surface. The growth rate of SiC was obtained using the surface diffusion length, the critical saturation and chemical equilibrium constant of reaction system. And the value was in agreement with the experimental results.

Growth, Defects and Electrooptic Properties of RbTiOAsO4 Crystal

RbTiOAsO4 (RTA) crystals of high optical quality were grown with flux method. The defects of RTA crystals are mainly growth striations, growth sector boundaries and sometimes ferroelectric domains. The refractive indices and electrooptic coefficients were measured together with dielectric constants, ionic conductivity and direct current resistivities. It is shown that RbTiOAsO4 is not only as good a nonlinear optical crystal as KTiOPO4 but also a superior electrooptic crystal.