No abstract

In order to improve the performance of AlGaN-based deep ultraviolet lightemitting diodes (UV LEDs), the optical and physical properties of AlGaN-based deep UV LEDs with a p-type and thickened last quantum barrier (LQB) are studied numerically. The output power-current performance curves, internal quantum efficiency, electroluminescence intensity, energy band diagrams, distributions of carrier concentrations, and the radiative recombination rates in the active region are investigated by Advance Physical Model of Semiconductor Devices (APSYS) software. The results reveal that, compared with the conventional one, the AlGaN-based deep UV LED with a p-type and thickened LQB achieves a remarkable improvement in performance, which is mainly attributed to the enhancement of hole injection and electron confinement.

AlGaN has attracted considerable interest as a wide (direct)-band-gap semiconductor with high thermal and mechanical stability. Thus, it can be used to develop optoelectronic devices operating within the ultraviolet region at high power and under harsh environmental conditions. Despite their recognized prospective applications, Al-rich AlGaN optical devices suffer from low external quantum efficiency. To trace the origin of the said problem, a cathodoluminescence system combined with two scanning probes was set up to investigate the cross-section luminescence of the sample related to application bias. The luminescence from the quantum wells in a deep ultraviolet light-emitting device was identified by layer-resolved spectroscopy. Results show that the primary radiative emission at the band edge exhibits an abnormal behavior, which is different from the other emission that is dependent on external electric fields. First-principles simulations demonstrate that the dispersive crystal field split-off hole (CH) band caused by hole deconfinement is responsible for the abnormal radiative emissions. Analysis of the constituent orbitals of the hole bands reveals a strong head-over-head lobe structure in the barrier along the [0001] direction in the p z orbitals, contributing mainly to the CH band. Meanwhile, a weak side-by-side (0001) in-plane lobe structure is present in the p x and p y orbitals, contributing to the heavy and light hole bands. This study may serve as a basis for further investigations on quantum efficiency improvement in high-Al-content AlGaN optoelectronic devices.