Threshold increase and lasing inhibition due to hexagonal-pyramid-shaped hillocks in AlGaN-based DUV laser diodes on single-crystal AlN substrate

Abstract

The presence of hexagonal-pyramid-shaped hillocks (HPHs) in AlGaN epitaxial films affects device character- istics; this effect is significant in DUV laser diodes (LDs) on AlN substrates, where the presence of HPHs under the p-electrode increases the threshold current density and inhibits the lasing. In this study, we investigated the difference between the lasing characteristics of LDs with and without HPHs. It was found that in the presence of HPHs, the threshold excitation power density increased and the slope efficiency decreased by optical excitation. To investigate the cause of these phenomena, we performed structural, optical, and electrical analyses of the HPHs. Various imaging techniques were used to directly capture the characteristics of the HPHs. As a result, we concluded that HPHs cause the degradation of LD characteristics due to a combination of structural, optical, and electrical factors.

Evaluating the performance of an AlGaN based deep ultraviolet laser diode using graded waveguide layer and graded cladding layer

“…The spontaneous polarization effect and quantum-confined Stark effect (QCSE) have great impacts on the separation of electron and hole wave functions. This results in the confinement of carriers in the active region of the device, leading to a decrease in the rate of radiation recombination, and electron leakage, and a reduction in output power [20], Moreover, hexagonal pyramids in AlGaN epitaxial films affect device characteristics [21]. To address these issues, many studies have been conducted.…”

Study of AlGaN-based deep ultraviolet laser diodes using one-way step-shaped quantum barriers and symmetrical step-shaped electron and hole blocking layers

“…[1][2][3][4][5] In addition, deep ultraviolet laser diodes (DUV-LDs) have been extensively studied and applied because of their small size, light weight, and high-level reliability. 6,7 However, due to the lattice mismatch and polarization of the electric field, the device still contains serious amounts of carrier leakage along with its weak carrier confinement capabilities and low output power. 8,9 To solve the above problems, Yi et al 10 proposed graded superlattice electron and hole blocking layers to reduce the carrier leakage, Shi et al 11 designed irregular electron and hole blocking layers to improve carrier confinement, and Xing et al 12 proposed a set of convex quantum wells in the multiple-quantum-wells (MQWs) AlGaN-based DUV-LDs to improve the carrier injection efficiency.…”

“…Due to the rapid development of III-nitride semiconductor materials and devices, the application of semiconductor light-emitting devices that operate in the deep ultraviolet band continues to expand, and they are widely used for pollution control, high-density information storage, lithography and disinfection 1 – 5 In addition, deep ultraviolet laser diodes (DUV-LDs) have been extensively studied and applied because of their small size, light weight, and high-level reliability 6 , 7 . However, due to the lattice mismatch and polarization of the electric field, the device still contains serious amounts of carrier leakage along with its weak carrier confinement capabilities and low output power 8 , 9 …”