Injection current, and temperature, dependences of the electroluminescence (EL) spectrum from green InGaN/GaN multiple quantum well (MQW)-based light-emitting diodes (LED) grown on a Si substrate, are investigated over a wide range of injection currents (0.5 µA-350 mA) and temperatures (6-350 K). The results show that an increasing temperature can result in the change of injection current-dependent behavior of the EL spectrum in initial current range. That is, with increasing the injection current in the low current range, the emission process of the MQWs is dominated by filling effect of low-energetic localized states at the low temperature range of around 6 K, and by Coulomb screening of the quantum confinement Stark effect followed by a filling effect of the higher levels of the low-energetic localized states at the intermediate temperature range of around 160 K. However, when the temperature is further raised to the higher temperature range of around 350 K, the emission process of the MQWs in the low current range is dominated by carrier-scattering effect followed by non-radiative recombination process. The aforementioned current-dependent behaviors of the EL spectrum are mainly attributed to the strong localized effect of the green LED, as confirmed by the anomalous temperature dependence of the EL spectrum measured at the low injection current of 5 µA. In addition, the injection current dependence of external quantum efficiency at different temperatures shows that, with increasing temperature from 6 to 350 K, in addition to the enhanced non-radiative recombination, electron overflow becomes more significant, especially in the higher temperature range above 300 K.

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The photoluminescence (PL) properties of blue multiple InGaN/GaN quantum well (BMQW) and green multiple InGaN/GaN quantum well (GMQW) formed on a single sapphire substrate are investigated. The results indicate that the peak energy of GMQW-related emission (P G) exhibits more significant “S-shaped” dependence on temperature than that of BMQW-related emission (P B), and the excitation power-dependent carrier-scattering effect is observed only in the P G emission; the excitation power-dependent total blue-shift (narrowing) of peak position (line-width) for the P G emission is more significant than that for the P B emission; the GMQW shows a lower internal quantum efficiency than the BMQW. All of these results can be attributed to the fact that the GMQW has higher indium content than the BMQW due to its lower growth temperature and late growth, and the higher indium content in the GMQW induces a more significant compositional fluctuation, a stronger quantum confined Stark effect, and more non-radiative centers.

Photoluminescence (PL) spectra of two different green InGaN/GaN multiple quantum well (MQW) samples S1 and S2, respectively with a higher growth temperature and a lower growth temperature of InGaN well layers are analyzed over a wide temperature range of 6 K–330 K and an excitation power range of 0.001 mW–75 mW. The excitation power-dependent PL peak energy and linewidth at 6 K show that in an initial excitation power range, the emission process of the MQW is dominated simultaneously by the combined effects of the carrier scattering and Coulomb screening for both the samples, and both the carrier scattering effect and the Coulomb screening effect are stronger for S2 than those for S1; in the highest excitation power range, the emission process of the MQWs is dominated by the filling effect of the high-energy localized states for S1, and by the Coulomb screening effect for S2. The behaviors can be attributed to the fact that sample S2 should have a higher amount of In content in the InGaN well layers than S1 because of the lower growth temperature, and this results in a stronger component fluctuation-induced potential fluctuation and a stronger well/barrier lattice mismatch-induced quantum-confined Stark effect. This explanation is also supported by other relevant measurements of the samples, such as temperature-dependent peak energy and excitation-power-dependent internal quantum efficiency.

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