Jian-Shihn Tsang

Activation of p-Type GaN in a Pure Oxygen Ambient

In this study, we activated p-type GaN in a pure oxygen ambient by rapid thermal annealing. The sheet resistance of p-type GaN was greatly reduced from > 107 Ω/\Box to 7.06 ×104 Ω/\Box after annealing in oxygen ambient at 500°C. The photoluminescence intensity of blue emission increased by one order of magnitude compared to the as-grown sample. Moreover, the sheet resistance of p-type GaN annealed in pure oxygen ambient is lower than that of p-type GaN annealed in nitrogen ambient. The carrier concentrations of the samples annealed in oxygen ambient are higher than those annealed in nitrogen ambient. The better activation of p-type GaN in oxygen ambient is due to the higher activity of oxygen than that of nitrogen. Oxygen would remove hydrogen that passivates Mg atoms by forming H2O at a lower temperature.

Optical and Electrical Characteristics of CO2-Laser-Treated Mg-Doped GaN Film

This work investigates the optical and electrical characteristics of CO 2-laser annealed Mg-doped GaN films to activate Mg-doped p-type GaN films. Results obtained from the CO 2 laser annealing investigation were similar to those of thermal annealing or low energy electron beam irradiation (LEEBI) treatment to activate the Mg-doped p-GaN films. The room-temperature photoluminescence (PL) intensity of the blue emission of the Mg-doped GaN film after 10 W laser annealing was approximately ten times stronger than that of the as-grown film. The resistivity of the Mg-doped GaN film decreased from 10 5 ˜¢cm to 2‐3˜¢cm as the laser annealing power rose above 6 W. The hole concentration of Mg-doped GaN film was approximately 1£ 10 17 cm i3 when the laser annealing power was 7.5 W.

Evidence of Zero Potential Spike Energy in AlGaAs/GaAs Heterostructure Emitter Bipolar Transistors

The potential spike energy at the emitter junction of AlGaAs/GaAs heterostructure emitter bipolar transistors (HEBT) was directly measured for the first time. Experimental data revealed that emitter thickness as thin as 300 A is thick enough to eliminate potential spike without compositional grading. It is found that the band bending in n-GaAs reduces the potential spike and hence very low offset voltage of 70 mV with high current gain of 150 can be obtained.

COMPOSITION MODULATION OF INXGA1-XAS QUANTUM-WELLS BY FAST DIMER ARSENIC FLUX CHANGE USING VALVED ARSENIC CRACKER

By fast change of the As 2 flux using a high temperature valved cracker, we have demonstrated the growth of strained In x Ga 1-x As quantum wells with different compositions. The modulation of composition is due to the change in incorporation rates of the group III atoms under different As 2 fluxes. Photoluminescence (PL) emission from the quantum wells clearly indicates the change in composition. A change of In composition from 20.6% to 8.5%, has been achieved by changing the V/III beam-equivalent-pressure (BEP) ratio from 11.7 to 3.9. By this technique of composition modulation, we have fabricated strained In 2 Ga 1-x As/GaAs single quantum well lasers with different emission wavelengths