Current Dependence of In-Plane Electroluminescence Distribution of In_<i>x</i>Ga_1-<i>x</i>N/GaN Multiple Quantum Well Light Emitting Diodes

Abstract

We have studied the radiative recombination mechanism of InxGa1-xN/GaN multiple quantum well (MQW) light emitting diodes (LEDs) by measuring the in-plane electroluminescence (EL) distribution with a near-field scanning optical microscope (NSOM) as a function of current over a range of 20 µA to 300 mA. We discuss the relationship between peak intensity and peak wavelength of local EL spectra with changing current. The region of strong EL intensity exhibits a long emission wavelength. Only a part of the wavelength distribution exhibits blue shift and the range of peak wavelength and intensity distribution becomes narrow with increasing current up to 10 mA. In the high-current region, the entire distribution shifts to shorter wavelength with increasing current. These findings suggest that localized carriers play a dominant role in the radiative recombination and those localized states saturate with increasing current in the low-current region, which leads to the blue shift of the longer wavelength part of the distributions due to state filling. In the high-current region the screening of the piezoelectric field by injected carriers is thought to be a dominant mechanism of the blue shift.