The optical properties of the violet, blue and green as well as blue-green dual-color InGaN/GaN Multiple Quantum Well (MQW) Light Emitting Diodes (LEDs) were investigated by photoluminescence (PL) under bias and electroluminescence (EL). The sample structures and Indium doping levels were shown to have great influences on the properties of the devices. Multiple rise and fall of the PL signals were observed under the decrease of the forward bias and increase of the reverse bias in the blue, green, and dual-wavelength LED samples. We suggest that the rise and fall of the PL spectrum are due to the increased electron and hole wavefunciton overlap and charge carrier escape, respectively, and that the multiple intensity peaks possibly originate from different Quantum Wells (QWs) in the sampl...[ Read more ]

The optical properties of the violet, blue and green as well as blue-green dual-color InGaN/GaN Multiple Quantum Well (MQW) Light Emitting Diodes (LEDs) were investigated by photoluminescence (PL) under bias and electroluminescence (EL). The sample structures and Indium doping levels were shown to have great influences on the properties of the devices. Multiple rise and fall of the PL signals were observed under the decrease of the forward bias and increase of the reverse bias in the blue, green, and dual-wavelength LED samples. We suggest that the rise and fall of the PL spectrum are due to the increased electron and hole wavefunciton overlap and charge carrier escape, respectively, and that the multiple intensity peaks possibly originate from different Quantum Wells (QWs) in the sample with different in-well fields depending on their positions. Our results indicated that the QWs in our samples make non-equivalent contributions to the PL emission. In addition, the emergence of a new higher energy spectral peak was found to considerably enhance the PL emission under reverse bias. We interpret the new peak as the emission from the excited state transition in the QW. On the other hand, the EL of blue LED showed a red-blue energy shift with the increase of the injection current. While the red shift was due to the enhancement of Quantum Confined Stark Effect (QCSE) by the forward bias, band filling effect was shown to play a dominate role for the blue shift.