Analysis of carrier injection efficiency of AlGaN UV-B laser diodes based on the relationship between threshold current density and cavity length

Abstract

The carrier injection efficiency η i of recently developed UV-B laser diodes (LDs) is estimated on the basis of fundamental calculations and measurements. A general procedure to estimate η i based on the relationship between the differential external quantum efficiency and the cavity length proves to be inadequate because of the large variation. To estimate η i without relying on the unstable output power, we analyze in detail how the threshold current density relates to the cavity length. By applying a light confinement factor of 3.5%, an internal loss of 10 cm−1, a current density of 0.56 kA cm−2 in the emission layers at zero gain, and a reflectivity of the mirror facet of 0.16, we estimate η i ≈ 3.5% for UV-B LDs. This low η i in UV-B LDs is due to unbalanced injection between electron and hole currents, which leads to electron overflow to the p-GaN side, as indicated by a simulation.

Development of High‐Reflectivity and Antireflection Dielectric Multilayer Mirrors for AlGaN‐Based Ultraviolet‐B Laser Diodes and their Device Applications

“…Previous studies have reported η i of 3.5% for UV-B laser diodes. [35] Furthermore, the α i estimated using the optical pumping variable stripe length method was roughly 10 cm À1 , as reported in refs. [36,37].…”

“…One possible reason is that η i tends to drop in AlGaN‐based UV devices as the injection current density increases because the amount of electrons overflowing to the p‐layer side increases as the injection current density increases. [ 35 ] It is possible that the value of η i is higher than in the uncoated condition due to the reduction in threshold current density caused by the mirror formation. Additionally, the edge surfaces of the UV‐B laser diode fabricated in this experiment were formed by a combination of ICP dry etching and wet etching with a TMAH solution.…”

Performance enhancement of ultraviolet-C AlGaN laser diode

“…SiLENSe™ enables the user to design various layers of III-Nitride LDs by using bandgap engineering principles [ 21 – 23 ]. If J n and J p are the current densities of electrons and holes, respectively, then using the Golden Fermi’s rule, we can determine: …”

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

“…One of the most important challenges is to reduce the threshold current density, which is still high compared with that of other nitride LDs. 10) In addition to the design of the film structure for high optical confinement, 11) low internal loss, 12,13) high IQE, 14,15) and improved electrical characteristics, 16,17) several other factors that can critically deteriorate the threshold current density should also be of concern. These include the generation of dislocations at the mesa edge 18) and the appearance of hexagonal-pyramidshaped hillocks (HPHs) 1) under the p-electrode.…”