Fabrication processing of ZnO-Based LEDs

To create efficient ZnO-based LEDs, it is important to develop practical etching process and optimize Ohmic contacts on ZnO. Wet etch rates at 25{degree sign}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 using HCl/H2O and H3PO4/H2O (2x10- 3-3.5x10-3 M) solutions. A comparison of Ti/Al/Pt/Au and Ti/Au Ohmic contacts on n-type Zn0.95Cd0.05O layers grown on ZnO buffer layers with GaN/sapphire templates shows a minimum contact resistivity of 2.3x10-4 Ω-cm2 obtained at 500{degree sign}C for Ti/Al/Pt/Au and 1.6x10-4 Ω-cm2 was obtained at 450{degree sign} C for Ti/Au. Ti/Au Ohmic contacts on heavily Al-doped (n~1019 cm-3) n-ZnO produce a low specific contact resistivity of 2.4x10-7 Ω- cm2 in the as-deposited condition and extremely low minimum values of 6x10-8 Ω-cm2 after annealing at 300{degree sign}C.