Selective and nonselective wet etching of Zn_0.9Mg_0.1O/ZnO

Wet etch rates at 25 degrees C for Zn0.9Mg0.1O grown on sapphire substrates by pulsed laser deposition (PLD) were in the range 300-1100 nm . min(-1) with HCl/H2O (5 x 10(-3)-2 x 10(-2) M) and 120-300 nm . min(-1) with H3PO4/H2O (5 X 10(-3)-2 x 10(-2) M). Both of these dilute mixtures exhibited diffusion-limited etching, with thermal activation energies of 2-3 kCal . mol(-1). 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(-1) in HCl/H2O (0.01-1.2 M) and 12-54 nm . min(-1) in H3PO4/H2O (0.02-0.15 M). The etching was reaction limited over the temperature range 25-75 degrees C, with activation energies close to 6 kCal . mol(-1). The resulting selectivity of Zn0.9Mg0.1O over ZnO can be a high as similar to 400 with HCl and similar to 30 with H3PO4.