The electrical and optical properties of Mg-doped InxGa1-xN were investigated herein. With an In mole fraction increase, the RT carrier concentration was increased exponentially. Compared to Mg-doped GaN layers, it was found that we could achieve a high (1.65 x 10(19) cm(-3)) hole concentration from the p-type InGaN with an indium content of 0.23. InGaN/GaN MQW blue LEDs without and with a 5-nm-thick p-type In0.23Ga0.77N contact layer were also successfully fabricated. We could reduce the 20 mA operation voltage from 3.78 V to 3.37 V by introducing a 5-nm-thick In0.23Ga0.77N layer on top of the p-type GaN layer and improve the blue LED EL intensity and output power by employing such a p-In0.23Ga0.77N layer. (c) 2005 Elsevier B.V. All rights reserved.