Laser-controlled etching of (Al,Ga)As epitaxial layers

We report a systematic study of laser-controlled etching behaviors of Al_xGa_1-xAs epitaxial layers (x from 0 to 0.5) by varying parameters such as laser power, beam scanning speed, beam duty cycle, number of scans and different doping types and concentrations. The laser source was an argon ion laser emitting at 514.5 nm and the etchant used was aqueous KOH (0.25 M). Etch rates of n-type layers were found to be significantly higher than those for p-type layers. Generally, higher etch rates were observed for layers with higher aluminium mole fraction. The etch rate was found to increase at an exponential rate with the laser power for CW beam, but this increase became linear when a chopped laser beam was used. The dependence of etch rates on different conditions can be largely accounted for by the differences in the built-in electric field at the surface as well as differences in the laser-induced local temperature rise in the layers.