Before processing the InGaAsN/GaAs edge emitting lasers, post-growth rapid thermal annealing (RTA) was applied on the wafer. Different RTA results in different threshold current density (J<sub>th</sub>). RTA at 720°C reduces the J<sub>th</sub> significantly but keeps the linear fit slope of J<sub>th</sub> vs 1/L (L is the cavity length). It indicates that RTA at 720°C can decrease the absorption losses. High temperature RTA at 890°C can dramatically decrease the linear fit slope, which indicates that the carrier conductivity is improved dramatically even the RTA time is only one second.
The GaN growth and Si-doped GaN are studied in this work. By means of x-ray diffraction and photoluminescence (PL) measurements we found that the GaN sample directly grown on GaAs substrate is pure cubic phase and that grown on AlAs buffer is pure hexagonal phase. The present study shows that the phase of GaN samples grown on GaAs substrates can be controlled using different buffer layers. The PL properties of Si-doped cubic GaN with different carrier concentrations were investigated at room temperature. It was found that when the carrier concentration is increased from 5 X 10<SUP>15</SUP> to 2 X 10<SUP>18</SUP>cm<SUP>-3</SUP>, the PL peak shifted towards low energy, from 3.246 to 3.227 eV, and the PL linewidth increased from 77.1 to 121 meV. The PL peak shift is explained by the bandgap narrowing effect due to the high doping concentration. The PL linewidth includes two parts: one is doping concentration-independent, which is caused by the imperfection of samples and phonon scattering; the other is doping concentration-dependent. We assign the second part to the broadening by the microscopic fluctuation of the doping concentration. The experimental measurements are in good agreement with the model.