Highly Controlled Wet and Dry Etching of Gallium Doped (Mg, Zn) O Epilayers Grown Using Metalorganic Vapor Phase Epitaxy

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The wet and dry etch rates of Ga-doped ZnO and MgxZn1-xO deposited on r-plane sapphire by metalorganic vapor phase epitaxy (MOVPE) were studied for magnesium content 0 ≤ x ≤ 0.3 using dilute phosphoric acid and halogen–based inductively coupled plasma reactive ion etching (ICP-RIE) respectively. A decrease in the dry etch rates with increasing magnesium content was observed along with relatively low thermal activation energies of 21, 25, and 55 meV corresponding to n-ZnO, n-Mg0.1Zn0.9O, and n-Mg0.3Zn0.7O films respectively. Conversely, wet etch rates increased with increasing magnesium content with corresponding thermal activation energies of 8.4, 5.5, and 4.3 kCal/mol for n-ZnO, n-Mg0.05Zn0.95O, and n-Mg0.1Zn0.9O epilayers respectively. The dominant rate-limiting step was determined to be ion-assisted desorption of the etch products including (Mg, Zn) Cl2 during ICP-RIE etching and the wet etch process transitioned from reaction rate-limited to diffusion rate-limited etching with increasing magnesium content.