Akira Uedono

Enhanced photo/electroluminescence properties of Eu-doped GaN through optimization of the growth temperature and Eu related defect environment

The influence of growth temperature on the surface morphology and luminescence properties of Eu-doped GaN layers grown by organometallic vapor phase epitaxy was investigated. By using a Eu source that does not contain oxygen in its molecular structure, and varying the growth temperature, the local defect environment around the Eu3+ ions was manipulated, yielding a higher emission intensity from the Eu3+ ions and a smoother sample surface. The optimal growth temperature was determined to be 960 °C and was used to fabricate a GaN-based red light-emitting diode with a significantly higher output power.

Electronic and optical characteristics of an m-plane GaN single crystal grown by hydride vapor phase epitaxy on a GaN seed synthesized by the ammonothermal method using an acidic mineralizer

Fundamental electronic and optical properties of a low-resistivity m-plane GaN single crystal, which was grown by hydride vapor phase epitaxy on a bulk GaN seed crystal synthesized by the ammonothermal method in supercritical ammonia using an acidic mineralizer, were investigated. The threading dislocation and basal-plane staking-fault densities of the crystal were around 104 cm−2 and less than 100 cm−1, respectively. Oxygen doping achieved a high electron concentration of 4 × 1018 cm−3 at room temperature. Accordingly, a photoluminescence (PL) band originating from the recombination of hot carriers was observed at low temperatures, even under weak excitation conditions. The simultaneous realization of low-level incorporation of Ga vacancies (VGa) less than 1016 cm−3 was confirmed by using the positron annihilation technique. Consistent with our long-standing claim that VGa complexes are the major nonradiative recombination centers in GaN, the fast-component PL lifetime of the near-band-edge emission at room temperature longer than 2 ns was achieved.

Thermal Behavior of Residual Defects in Low-Dose Arsenic- and Boron-Implanted Silicon After High-Temperature Rapid Thermal Annealing

We investigated the thermal behavior of defects remaining in low-dose (<;1013 cm-2) arsenic- and boron-implanted Si after high-temperature (1100 °C) rapid thermal annealing (RTA). The defects remaining after RTA were characterized as vacancy-type defects, and confirmed to be created by nonequilibrium states that occur during the extremely rapid cooling step of the RTA sequence. They were gradually removed by applying additional furnace annealing (FA) (i.e., thermal equilibrium heating process) at 300-400 °C. At the range of 500-600 °C, however, carbon- and oxygen-related point defects were newly created. These defects were confirmed to be eliminated at 700 °C, and the crystal quality was significantly improved. When using a rapid thermal process for heat treatment after low-dose impurity implantation, it is necessary to apply an equilibrium thermal treatment at >700 °C to remove residual damage as well as to activate impurities.