Investigation of the Nonthermal Mechanism of Efficiency Rolloff in InGaN Light-Emitting Diodes

We present a comparative study on the optical characteristics of InGaN-based multiple quantum well light-emitting diodes (LEDs) with peak emission ranging from green to ultraviolet (UV) over a wide injection range. It is found that by pulsing the LEDs with a duty cycle that is below 1%, thermally induced peak red shift and efficiency reduction are largely eliminated. The current dependence of both the quantum efficiency and peak shift appears to be a strong function of the indium content in the active region. The quantum efficiencies of the blue and green LEDs peak at very low currents and dramatically decrease at high currents, whereas the UV LED has a nearly constant quantum efficiency under high injection conditions. In contrast to the minimal current- induced energy shift in the UV LED, a monotonic blue shift of the peak energy, which has a total amount of ~110 meV-1 kA/cm2, is seen for the green LED. These results offer a strong support for the argument that the current overflow from localized states is the major nonthermal mechanism underlying the efficiency rolloff in InGaN-based visible LEDs.

[1]  S. LeBoeuf,et al.  Temperature-dependent electroluminescence in InGaN/GaN multiple-quantum-well light-emitting diodes , 2003 .

[2]  Michael R. Krames,et al.  Auger recombination in InGaN measured by photoluminescence , 2007 .

[3]  J. Kretchmer,et al.  Diffusion and tunneling currents in GaN/InGaN multiple quantum well light-emitting diodes , 2002, IEEE Electron Device Letters.

[4]  Sandor Kokenyesi,et al.  Fully-screened polarization-induced electric fields in blue∕violet InGaN∕GaN light-emitting devices grown on bulk GaN , 2005 .

[5]  Shuji Nakamura,et al.  The Blue Laser Diode: GaN based Light Emitters and Lasers , 1997 .

[6]  Takayuki Sota,et al.  Luminescence spectra from InGaN multiquantum wells heavily doped with Si , 1998 .

[7]  Joachim Wagner,et al.  Injection level dependent luminescence characteristics of UV–violet emitting (AlGaIn)N LED structures , 2007 .

[8]  Takashi Mukai,et al.  Confocal microphotoluminescence of InGaN-based light-emitting diodes , 2005 .

[9]  Yue-Kai Huang,et al.  Efficiency droop behaviors of InGaN∕GaN multiple-quantum-well light-emitting diodes with varying quantum well thickness , 2007 .

[10]  Shuji Nakamura,et al.  The blue laser diode-the complete story , 2000 .

[11]  Xian-An Cao,et al.  High-power and reliable operation of vertical light-emitting diodes on bulk GaN , 2004 .

[12]  J.Y. Tsao,et al.  Solid-state lighting: lamps, chips and materials for tomorrow , 2005, (CLEO). Conference on Lasers and Electro-Optics, 2005..

[13]  D. A. Zakheim,et al.  Analysis of processes limiting quantum efficiency of AlGaInN LEDs at high pumping , 2007 .

[14]  Bo E. Sernelius,et al.  Defect related issues in the current roll-off in InGaN based light emitting diodes , 2007 .

[15]  Peter Blood,et al.  Carrier leakage in InGaN quantum well light-emitting diodes emitting at 480 nm , 2003, Applied Physics Letters.

[16]  X.A. Cao,et al.  Temperature-dependent electroluminescence of AlGaN-based UV LEDs , 2006, IEEE Electron Device Letters.