Advances in ZnO-based materials for light emitting diodes

• A critical analysis of the status of p-type doping of ZnO is presented.
• The performance of ZnO-based light-emitting diodes is reviewed.
• The role of defects and self-compensation in limiting the maximum p-type concentration in ZnO is emphasized.

ZnO and related semiconductors are alternatives to GaN-based compounds for fabrication of UV/blue light emitting diodes (LEDs). Progress in development of ZnO LEDs has been disappointing due to the difficulty of achieving robust p-type doping and the low crystal quality of heterojunctions and quantum wells. We critically review reports of p-type doping using group V impurities and summarize recent progress and prospects for further advancement of ZnO-based light emitters.