Effects of interfacial layers in InGaNGaN quantum-well structures on their optical and nanostructural properties

We compared the optical properties and material nanostructures between several InGaNGaN multiple quantum-well (QW) samples of different interfacial layers. In some of the samples, InN interfacial layers were inserted between the wells and barriers to improve the QW quality and hence the light-emission efficiency. Compared with a widely used barrier-doped QW structure, the insertions of the InN interfacial layers (silicon doped or undoped) do enhance the photon emission efficiencies. Of the two samples with InN interfacial layers, the one with intrinsic InN interfacial layers had the higher photoluminescence (PL) and electroluminescence (EL) efficiencies. Cluster structures are clearly observed in this sample, resulting in strong carrier localization. In this sample, we also observed a temperature-dependent S-shape variation in the PL spectral peak, a strong photoluminescence excitation (PLE) intensity, and a steep PL decay time variation beyond its peak as a function of temperature. On the other hand, both carrier localization and quantum-confined Stark effect (QCSE) were relatively weaker in another sample, which includes silicon-doped InN interfacial layers. The broadening of the InGaN well layers, in one sample, by inserting silicon-doped InGaN interfacial layers led to the sharpest cluster structures and the strongest carrier localization among the four samples. Therefore, in this sample we observed quite high PL and EL efficiencies, increasing EL spectral peak energy with temperature, a strong PLE intensity, and a steep PL decay time variation beyond its peak in temperature dependence. Compared with the aforementioned samples, the widely used QW structure (the reference sample) shows the lowest PL and EL emission efficiencies, the smallest PL and EL emission photon energies, and the generally longest PL decay times. This suggests that the QCSE is the strongest in this sample.