Facet formation of a GaN-based device using chemically assisted ion beam etching with a photoresist mask

The etch characteristics of GaN were investigated using chemically assisted ion beam etching (CAIBE) for Cl₂ as a function of tilt angle. With increasing tilt angle the measured GaN etch rate showed a maximum at 30° similar to the effect of tilt angle on the sputter yield. The etch profiles of GaN etched by tilting the substrate less than 20° showed sidewall trenching. When the tilt angle was more than 30°, an etch tail was observed at the bottom of the etched structure. With the Cl₂ CAIBE, the anisotropy of the GaN etch profile was enhanced as the tilt angle was increased, and a vertical etch profile could be obtained at a 50° tilt angle. The sidewall roughness of the etched GaN laser device varied with the Cl₂ flow rate and ion beam voltage. A highly anisotropic etch profile with a smooth sidewall could be obtained by optimization of the ion beam voltage/current and Cl₂ flow rate. The surface of GaN etched by the Cl₂ CAIBE system showed a Ga-deficient surface due to the removal of Ga by the formation of GaCl_x.