Temperature and current dependence of the optical intensity and energy shift in blue InGaN-based light-emitting diodes: comparison between electroluminescence and cathodoluminescence
Optical spectra of InGaN-based multiple quantum well test structures have been measured by complementary techniques: electroluminescence (EL) and cathodoluminescence (CL). A strong temperature and current dependence of the peak energy is found, highlighting the existence of a distribution of InGaN localized states, with a broadening parameter ranging between 29 and 18 meV, and the presence of internal fields screened with different efficiencies by means of the external excitations. The effects of the different injection mechanisms, mainly with (EL) or without (CL) an external bias, are underlined also by the evolution of the emission intensity with temperature. In CL, it shows a continuous decay versus T, characterized by estimated activation energies of 26 ± 14 meV and 136 ± 20 meV, due to carrier thermal escape processes. In EL, a non-monotonic temperature dependence at a fixed current is revealed. The existence of an intensity maximum and its temperature position, increasing from 120 to 180 K for currents ranging from 0.05 to 2 mA, are discussed.