Anomalous excitation dependence of electroluminescence in InGaN∕GaN light-emitting diodes

Abstract

We have systematically investigated the anomalous excitation dependence of the electroluminescence (EL) in InGaN∕GaN multiple-quantum-well light-emitting diodes over a temperature range from 300to20K. Initially, an increase in the emission intensity occurred upon decreasing the temperature, until a maximum was reached at the temperature Tm. A blueshift in the position of the EL peak was followed by a redshift that occurred at the crossover temperature Tc. Both of these characteristic temperatures correlate with the presence of statistic microbarriers arising from potential inhomogeneity. The higher the In content incorporated into the heterobarriers, named multiple quantum barriers, the lower the values of Tm and Tc obtained from the spectral observations; this phenomenon implies an augmentation in the microscopic nonradiative transport through the microbarriers. An increase in the injection current also led to decreases in both of these characteristic temperatures. In addition, a functional correlation exists between the values of Tc and Tm. All of these experimental results suggest that InGaN∕GaN microstructures can be viewed as disordered collections of InGaN nanocrystallites. Further experimental verification will be necessary if this phenomenological model is to be used to account for the properties of any other disorderlike heteromaterials.