High selective etching GaAs/Al0.3Ga0.7As for the high electron mobility transistor (HEMT) applications using citric buffer solution

High selective wet etching of GaAs on Al_0.3Ga_0.7As can be realized using citric buffer (citric acid/H₂O₂/H₂O) solution. The selectivity of GaAs to Al_0.3Ga_0.7As was as high as 264 at 23 °C by optimizing the pH and citric acid/hydrogen peroxide ratio having the etch rate of GaAs is 18.08 Å/s and etch rate of Al_0.3Ga_0.7As is 0.0685 Å/s at a pH of 2.32. The etch stop mechanism is attributed to the formation of dense oxide Al₂O₃ on Al_0.3Ga_0.7As. This finds applications in high electron mobility transistors (HEMT) gate recess processes, no obvious drain current decrease can be perceived even after 12 min over etching.