Growth of flat p‐GaN contact layer by pulse flow method for high light‐extraction AlGaN deep‐UV LEDs with Al‐based electrode

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)