Selective and nonselective wet etching of ZnMgO/ZnO

Wet etch rates at 25°C for ZnMgO grown on sapphire substrates by pulsed laser deposition (PLD) were in the range 300–1100 nm · min with HCl/HO (5×10−2×10 M) and 120–300 nm · min with HPO/HO (5×10−2×10 M). Both of these dilute mixtures exhibited diffusion-limited etching, with thermal activation energies of 2–3 kCal · mol. By sharp contrast, the etch rates for ZnO also grown on sapphire by PLD were much slower in similar solutions, with rates of 1.2–50 nm · min in HCl/HO (0.01–1.2 M) and 12–54 nm · min in HPO/HO (0.02–0.15 M). The etching was reaction limited over the temperature range 25–75°C, with activation energies close to 6 kCal · mol. The resulting selectivity of ZnMgO over ZnO can be a high as ∼400 with HCl and ∼30 with HPO.