Thermal and carrier transport originating from photon recycling and non-radiative recombination in laser micromachining of GaAs thin films

Coupled thermal and carrier transports (electron/ hole generation, recombination, diffusion and drifting) in laser photoetching of GaAs thin film is investigated. A new volumetric heating mechanism originating from SRH (Shockley– Read–Hall) non-radiative recombination and photon recycling is proposed and modeled based on recent experimental findings. Both volumetric SRH heating and Joule heating are found to be important in the carrier transport, as well as the etching process. SRH heating and Joule heating are primarily confined within the space-charge region, which is about 20 nm from the GaAs surface. The surface temperature rises rapidly as the laser intensity exceeds 105 W/m2. Below a laser intensity of 105 W/m2, the thermal effect is negligible. The etch rate is found to be dependent on the competition between photovoltaic and photothermal effects on surface potential. At high laser intensity, the etch rate is increased by more than 100%, due to SRH and Joule heating. PACS 44.10.+i; 72.40.+w; 73.61.Ey