Etching of GaN Using Phosphoric Acid

Hot phosphoric acid is found to be useful for etching and characterizing epitaxial crystals grown on (0001) sapphire substrates. The obtained etch rates are 0.2–1.0 μm/min and the activation energy is about 4.4 kcal/mole in the temperature region of 50°–200°C. Hydration of Ga ion is considered the rate‐determining step of the etching action. The x‐ray diffraction and the infrared spectrometric studies indicate that the ortho and meta phosphoric ions play an important role as attacking ions in etching. This phosphoric acid etching reveals crystal defects in undoped (n), Zn‐doped (i), and i‐n structure epitaxial crystals. Conical hexagonal pyramid pits and truncated hexagonal pits develop in the undoped layers, and they tend to be arranged along the slip direction and are attributed to certain dislocations. These hexagonal pits are densely generated near the interface of the epitaxial layer and the substrate. The density of the pits decreases exponentially with crystal growth. The pits are apt to increase in density and size when the carrier concentration is high (10 19 –10 20 cm 3 ). The rounded etch figures develop in Zn‐doped crystals and sometimes in the undoped crystals with a high carrier concentration (10 19 cm −3 ). Etching also indicates that there is a significant difference in growth patterns between the Zn‐doped and the undoped crystals even if the Zn‐doped layer is continuously deposited on the undoped layer. This implies a difference in the crystal growth mechanism between these crystals.