AlGaN/GaN multiple quantum wells (MQWs), as the core light-emitting regions of optoelectronic devices such as ultraviolet light-emitting diodes (LEDs) and laser diodes (LDs), greatly impact the performance of such devices. However, due to the large lattice mismatch between the AlGaN material and the substrate, a large number of defects exist in AlGaN/GaN MQWs, which seriously affects the luminescence characteristics of the MQWs. In addition, polarization, quantum confinement Stark effect, and localized state effect can also impact the luminescence efficiency of MQWs; in particular, the localized effect has a significant influence on the luminescence uniformity of ultraviolet MQWs. Therefore, study of the factors affecting the luminescence of AlGaN/GaN UV MQWs will contribute to a better understanding of the luminescence mechanism of MQWs, and leads to high-performance GaN-based ultraviolet optoelectronic devices.

In this work, three samples of AlGaN/GaN MQWs are grown on sapphire substrates using metal-organic chemical vapor deposition (MOCVD). First, the components and thicknesses of the samples are determined via X-ray diffractometer (XRD). Their room-temperature photoluminescence (PL) spectra are then obtained using a PL system with a 325 nm He-Cd laser as the excitation source. Finally, the luminescence mechanism of the sample is analyzed via temperature dependent PL spectroscopy.

From the room-temperature PL spectra, the luminescence intensity of the quantum well first increases and then decreases as the well width increases (Fig. 1). In addition, temperature dependent photoluminescence spectroscopy tests indicate that as the temperature increases, the emission wavelength of the ultraviolet quantum well first shifts blue and then red; this phenomenon is more apparent for the samples with wider wells (Figs. 2 and 3). Furthermore, the luminescence of the ultraviolet quantum well exhibits localized state effects similar to those from blue-green light quantum wells, which becomes more significant as the well width increases. This may be due to the fact that the polarization properties, fluctuations in well width, and inhomogeneity of the Al composition of the barrier layer together lead to varying quantum confinement effects in the well layer.

Three AlGaN/GaN ultraviolet MQW samples with different well widths are epitaxially grown on sapphire substrates using MOCVD, and their luminescence characteristics are investigated. As a result, excessively narrow well layers can lead to a decrease in PL intensity and a blue shift in the MQW peak, while increasing the quantum well width appropriately is beneficial for improving PL luminescence intensity. This phenomenon may be due to polarization characteristics, fluctuations in well width, and uneven Al composition in the barrier layer. Moreover, wide wells have different quantum confinement effects, resulting in localized state effects similar to those from blue-green light quantum wells, thereby enhancing ultraviolet luminescence intensity.