Phase separation in InGaN/GaN multiple quantum wells and its relation to brightness of blue and green LEDs

InGaN/GaN multiple quantum wells (MQW) and high-brightness MQW light-emitti ng diodes were grown by production scale metal-organic chemical vapor depos ition (MOCVD). We have found that the extent of InGaN phase separation in I nGaN MQWs depends strongly on growth conditions. Multiple peaks in photolum inescence (PL) of InGaN/GaN MQWs and electroluminescence (EL) of MQW LEDs c an be observed at room temperature. In the presence of InGaN phase separati on, photoluminescence of MQW is red-shifted with respect to the expected wa velength calculated for the apparent indium composition determined by X-ray diffraction (XRD). We have determined that InGaN phase separation is neces sary for high brightness electroluminescence in LEDs. Under optimal growth conditions, MQWs with very well-defined XRD satellite peaks and PL in the w avelength range of (450-520nm) can be achieved. High-brightness LEDs emitti ng at 480 nm have been successfully fabricated with an output power well be tter than 2 mW at 20 mA and with a forward voltage less than 4 V. (C) 1998 Elsevier Science B.V. All rights reserved.