Growth of flat p-GaN contact layer by pulse flow method for high light-extraction AlGaN deep-UV LEDs with Al-based electrode
Abstract
Improvement of light extraction efficiency (LEE) is strongly demanded in an AlGaN-based deep ultraviolet (DUV) light-emitting diode (LED), because the LEE of AlGaN DUV LED is low (usually below 10%) due to the light absorption at around p-GaN contact layer and p-type electrode. We have demonstrated improvement of LEE of AlGaN DUV LEDs by using thin p-GaN contact layer and using Al-based high-reflectivity p-electrode. It was difficult to grow thin and flat p-type GaN layers with heavy Mg-doping on high-Al-content AlGaN layers. We demonstrated the growth of flat and thin p-GaN contact layer by using ‘an NH3 pulse-flow growth method’. We investigated the growth conditions for thin p-GaN contact layer with high-hole-concentration using the NH3 pulse-flow growth method. The surface roughness of the p-GaN layer on high-Al-content p-AlGaN was markedly improved by using an NH3 pulse-flow growth method. We fabricated 250 nm-band AlGaN quantum well (QW) DUV LEDs with thin p-GaN contact layers grown by an NH3 pulse-flow growth method. We observed single-peaked operation spectrum for the 251 nm AlGaN MQW LED. The maximum output power and external quantum efficiencies (EQE) were 17.7 mW and 1.32%, respectively, measured under room temperature cw operation. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
