The internal quantum efficiency (IQE) of InGaN near-UV light-emitting diodes with different threading dislocation densities (TDDs) was studied by using excitation power density and temperature-dependent photoluminescence spectroscopy. The IQE was evaluated as functions of excitation density and temperature under band-to-band and selective excitation of the InGaN active layers. The IQE curves under weak excitation densities were analyzed with a rate equation model of radiative and nonradiative recombination of excitons, in which the exciton localization and the filling of nonradiative recombination centers (NRCs) were considered. Based on the analysis, we discussed the effects of filling NRCs on the IQE as functions of TDD and temperature and we clarified that the increase in the IQE at lower excitation densities was caused by filling NRCs. The analysis also indicated whether the maximum IQE value reached 100% at low temperatures.
The optical polarization of Si-doped AlxGa1−xN epitaxial layers (x=0.37–0.95) has been studied by means of photoluminescence (PL) spectroscopy. The predominant polarization component of the band-edge PL switched from E⊥c to E∥c at an Al composition between 0.68 and 0.81. This critical Al composition was much higher than in previous reports for AlGaN epitaxial layers. In addition, the predominant polarization in Al0.55Ga0.45N epitaxial layers switched from E⊥c to E∥c with increasing Si concentration. Therefore, the topmost valence band changed from the heavy-hole band to the crystal-field split-off-hole band with decreasing in-plane compressive strain induced by Si doping.
Internal quantum efficiency (IQE) of AlGaN‐based multiple quantum wells (MQWs) on face‐to‐face‐annealed sputter‐deposited AlN templates is examined by photoluminescence spectroscopy. The excitation power density dependence of IQE is evaluated as a function of temperature under the selective excitation of the quantum wells. The temperature dependences of the maximum IQE and the corresponding excitation power density (EPD) are analyzed based on the rate equation models for carriers and excitons. The decrease of the maximum IQE and increase of the corresponding EPD are mainly due to the increase in the nonradiative recombination rate via nonradiative recombination centers. Furthermore, the nonradiative recombination rate for the MQW with an emission wavelength around 220 nm is activated at a lower temperature than the other samples, which is expected to lead to the lower IQE of the MQW with an emission wavelength around 220 nm.
