Towards Efficient Electrically-Driven Deep UVC Lasing: Challenges and Opportunities

Abstract

The major issues confronting the performance of deep-UV (DUV) laser diodes (LDs) are reviewed along with the different approaches aimed at performance improvement. The impact of threading dislocations on the laser threshold current, limitations on heavy n- and p-doping in Al-rich AlGaN alloys, unavoidable electron leakage into the p-layers of (0001) LD structures, implementation of tunnel junctions, and non-uniform hole injection into multiple quantum wells in the active region are discussed. Special attention is paid to the current status of n- and p-type doping and threading dislocation density reduction, both being the factors largely determining the performance of DUV-LDs. It is shown that most of the above problems originate from intrinsic properties of the wide-bandgap AlGaN semiconductors, which emphasizes their fundamental role in the limitation of deep-UV LD performance. Among various remedies, novel promising technological and design approaches, such as high-temperature face-to-face annealing and distributed polarization doping, are discussed. Whenever possible, we provided a comparison between the growth capabilities of MOVPE and MBE techniques to fabricate DUV-LD structures.

Carrier Recombination in Nitride-Based Light-Emitting Devices: Multiphonon Processes, Excited Defects, and Disordered Heterointerfaces

“…It should be noted that we arrived at this conclusion using simpler and more accessible experimental methods than those used in the referenced works. Furthermore, the methods used allowed us to identify two mechanisms of carrier loss caused by their interaction with EDs, rather than with SRH defects, as assumed in numerous studies [2,[5][6][7]. Carrier losses caused by the involvement of these mechanisms result in a very slight increase in EQE of 1-2% with a several-fold increase in j in the range of j > 2 A/cm 2 .…”

“…The complexities of charge carrier recombination processes in nitride-based lightemitting devices (LEDs) are crucial in understanding various related physical phenomena. These phenomena include the efficiency droop effect, characterized by a decrease in efficiency with increasing injection currents, a reduction in efficiency due to higher indium or aluminium content (known as the "green gap" issue), notably low efficiency levels of UV LEDs using AlGaN alloys, reversible degradation processes, the short lifespan of laser diodes, and the creation of defects under injection current [1][2][3][4][5][6][7][8][9][10].…”

“…Furthermore, the ABC model assumes relatively ideal heterointerfaces and uniform distributions of electrons and holes in the multiple QWs. The observed deviations in real LED characteristics from those calculated within the framework of the ABC model are often attributed to imperfections in technological processes and such effects as the Stark effect, low hole concentration, high dislocation density, Auger recombination, and random alloy fluctuations (RAFs) [2,5,7]. However, during analysis, only a subset of these factors is typically considered, leaving others unexplored.…”

Electron-Beam Pumped UVC-Emitters Based on (Al, Ga)N Material System

“…At present, several scientific groups are engaged in the development of alternative semiconductor UVC lasers based on AlGaN heterostructures, but this topic is beyond the scope of this review. A detailed analysis of this problem can be found in a recent review by Nikishin et al [44].…”

Electron-Beam-Pumped UVC Emitters Based on an (Al,Ga)N Material System

“…At present, several scientific groups are engaged in the development of alternative semiconductor UVC lasers based on AlGaN heterostructures, but this topic is beyond the scope of this review. A detailed analysis of the challenges and implementation of efficient electrically driven UVC lasing can be found in a recent review by Nikishin et al [ 46 ].…”