350-nm band edge-emitting laser diodes enabled by low-dislocation-density AlGaN templates
Realization of efficient laser diodes with ultra-violet (UV) emission from ~260-360 nm would enable many applications including fluorescence-based biological agent detection, sterilization, and portable water purification. While InGaN-based laser diodes are well developed down to ~370 nm, achieving shorter UV wavelengths requires higher Al-content AlGaN alloys with increasing challenges in achieving p-type doping, strain-management, and low threading-dislocation-density (TDD) AlGaN templates. Given these challenges, few groups have reported AlGaN-based edge-emitting laser diodes (LDs) with emission <; 355 nm.[1, 2] Most recently, random lasing via Anderson localization in AlGaN nanowire structures has demonstrated a novel approach to realizing deep-UV laser diodes.[3].
Entirely Crack-Free Ultraviolet GaN/AlGaN Laser Diodes Grown on 2-in. Sapphire Substrate
We have succeeded in fabricating ultraviolet (UV) GaN/AlGaN laser diodes without any crack generation on a whole 2-in. sapphire substrate using a hetero-facet-controlled epitaxial lateral overgrowth (hetero-FACELO) method. The UV laser diodes lased in the peak wavelength range from 355.4 to 361.6 nm under a pulsed current operation at room temperature. We have also investigated both parameters, material gain and optical-internal loss in GaN/AlGaN multiple quantum wells (MQWs). The actual threshold currents of the UV laser diodes were practically in agreement with the estimated threshold current from these parameters. This layer structure is one of the solutions for the purpose of high-yield production of UV photonic devices.
Optical gain characteristics of non-polar Al-rich AlGaN/AlN quantum well structures
Optical properties of non-polar Al-rich AlGaN/AlN quantum well (QW) structures were investigated using the multiband effective-mass theory and non-Markovian optical model with the many-body effect. These results are compared with those of the c-plane, i.e., the (0001)-oriented QW structures. The theoretical PL transition wavelength is found to agree well with the experimental result. The optical gain for the x′-polarization is much larger than that for the y′-polarization because the optical matrix element for the x′-polarization is larger than for the y′-polarization. The x′-direction in the non-poalr plane corresponds to c-axis direction. Also, the optical gain for the x′-polarization is shown to decrease with increasing Al composition. This is mainly attribute to the fact that the optical matrix element is decreased due to the reduction in the electron-hole overlap for QW structures with higher Al contents.