Abnormal Radiative Interband Transitions in High-Al-Content AlGaN Quantum Wells Induced by Polarized Orbitals

Abstract

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.

Effect of electrical injection-induced stress on interband transitions in high Al content AlGaN MQWs

“…These features are agree with the simulated results reported in literature. 20 As the tensile strain increases to +2%, the D cr further decreases to À199 meV, and the dispersion of CH become stronger. These unconventional features indicate that the CH bands become more dominant at the top of valence bands, and less holes are conned in the QWs as the tensile strain increases.…”

“…The transition probability is proportional to the momentum matrix element (MME). The degree of the in-plane polarization as a function of strain were calculated from the MME of HH, LH and CH bands restricted to G to A of the Brillouin zone, 12,[19][20][21] as shown in Fig. 4(c).…”

“…5(b), indicating hole-states are strongly localized in the QWs. 20 Therefore, a dominate TE (Etc) polarized emission and high emission efficiency can be expected when a compressive stress is generated in the high Al-content MQWs active region. 6,9,23,24 Fundamentally, the light emission efficiency is determined by the states of the top of valence bands.…”

“…The density of states r r is calculated by the partial charge density of the quantum levels restricted to the G to A of the Brillouin zone. 20 Accordingly, the transition ranging from G to A between the top of valence bands and conduction band minimum has become the focus. As a result, the total spontaneous emission rate R sp under different strain is derived in Fig.…”

Smart Wide‐Bandgap Omnidirectional Reflector as an Effective Hole‐Injection Electrode for Deep‐UV Light‐Emitting Diodes

“…Compact solid‐state deep‐ultraviolet (DUV) light sources have attracted considerable attention for various applications including sterilization, water purification, lithography, and medical/biological detection . After the development of GaN‐based blue‐light‐emitting diodes (LEDs), AlGaN‐based DUV‐LEDs covering the whole UV spectral range through the control of the Al content were realized, despite low efficiencies .…”