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We have investigated temperature-dependent photoluminescence (PL) of green and blue light-emitting InGaN/GaN multiple quantum wells at different excitation powers. Two InGaN-related PL peaks centered at around 2.4 and 2.7 eV are assigned to quasi-quantum dot (QD) emissions (PD) and the InGaN matrix emission (PM), respectively, due to a strong phase separation confirmed by high-resolution transmission electron microscopy. In contrast to the S-shaped temperature-dependent behavior of the PM peak energy, the PD peak energy initially decreased and then increased with increasing temperature up to 300 K, indicating that the carriers within QDs relax to stronger localized states first and then are thermalized to higher levels with increasing temperature. Interestingly, it was found that with increasing temperature both the emission intensities initially increased and then decreased. This behavior was attributed to an increased carrier localization effect and then enhanced non-radiative recombination with increasing temperature; this was consistent with the temperature-related behavior of the emission energy. In addition, the temperature dependence of the intensity ratio of PM to PD further shows that the enhanced thermalization effect of the carriers inside the QDs with increasing temperature, resulted in the significant decrease of PD intensity relative to PM intensity. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) properties of InGaN/GaN multiple quantum wells are studied. Two InGaN-related peaks are observed in the full PL spectrum and are assigned to the quasi-quantum dots (QDs) (2.42 eV) and the InGaN matrix (2.66 eV), due to a strong phase separation. As the carriers transfer from the matrix down to the QDs, an increase of the QDs-related PL intensity (ID) accompanied by the decrease of the matrix-related PL intensity (IM) results. A slight increase of the total PL intensity is also observed, and is attributed to the QDs providing deep potential levels to suppress the outflow of carriers toward surrounding nonradiative centers. A piezoelectric field resulting from the high indium content inside the QDs is observed, which is speculated from Coulomb screening effect. Additionally, we find that the sublinear dependence of the ID on excitation power (P) is due to the saturation of the QDs states, while the superlinear dependence of the IM on P is simultaneously attributed to the suppression of the carriers transferring from the matrix to the QDs and the saturation of the nonradiative centers in the matrix. [ABSTRACT FROM AUTHOR]

Abstract: Electroluminescence (EL) spectra of blue InGaN/GaN multiple-quantum-well light-emitting diode (LED) have been investigated over a wide range of injection current (0.001–200mA) and at various temperatures (6–300K). Surprisingly, with increasing the injection current the EL peak energy shows an initial blueshift accompanied by a broadening of the EL linewidth at low temperatures (below 30K). This trend differs from the usual photoluminescence (PL) measurement results, which have shown that with increasing the optical excitation power the PL peak energy gave an initial blueshift accompanied by a narrowing of the PL linewidth at low temperatures. The anomalous current behavior of the EL spectra may be attributed to electron leakage results in the failure of Coulomb screening effect and the relative enhancement of the low-energetic localized state filling at low temperatures and low currents. The electron leakage for the LED is further confirmed by both the current dependence of the EL intensity and the temperature dependence of the EL efficiency. [Copyright &y& Elsevier]