Diffusion-controlled selective wet etching of ZnCdO over ZnO

Wet etch rates at 25 degrees C for Zn0.95Cd0.05O grown on sapphire substrates by rf plasma-assisted molecular beam epitaxy were in the range 30-90 nm min(-1) with HCl/H2O and H3PO4/H2O (2 x 10(-3) to 3.5 x 10(-3) M) mixtures. Both of these dilute mixtures exhibited diffusion-limited etching for the ZnCdO, with thermal activation energies of similar to 0.4 kcal mol(-1). Under these conditions, the etching was selective over ZnO grown in a similar fashion. The maximum selectivities for the Zn0.95Cd0.05O over ZnO were similar to 50 for the HCl/H2O mixture and similar to 15 for the H3PO4/H2O mixture. The etching of the ZnO at lower dilution factors (2 x 10(-3) to 10(-1) M) was reaction-limited over the temperature range 25-75 degrees C, with activation energies close to 6 kcal mol(-1). Simple photoresist masking can be used with both etch mixtures. (c) 2005 The Electrochemical Society.