Assessment of the Feasibility of a Semi-Monolithic GaN VCSEL Structure Emitting at 450 nm Based on Electrical and Thermal Modeling

Abstract

This work presents a possible structure of a semi-monolithic GaN-based VCSEL with a tunnel junction, emitting at 450 nm and incorporating a nanoporous GaN (NP-GaN)/GaN distributed Bragg reflector (DBR). Self-consistent electrothermal simulations were performed to examine how the current-aperture radius and cavity length affect current-crowding and selfheating within the active region. Increasing the cavity length from 1λ to 10λ was found to markedly improve current uniformity and heat dissipation, while smaller apertures yielded lower maximum temperatures; a cavity length of 5λ combined with a 3 µm aperture radius was identified as the optimal design compromise. The influence of NP-GaN porosity on the thermal resistance of the rear DBR was further analyzed for two refractive-index models, linear and quadratic, while maintaining a target reflectivity above 99.98%. A porosity of about 30% offered the best trade-off between the number of required DBR pairs and thermal performance, giving a maximum device temperature of 317.1–317.6 K. Comparison with alternative AlInN/GaN and AlScN/GaN DBRs showed that the NP-GaN/GaN mirror achieves the lowest maximum temperature and requires fewer layer pairs, despite the technological challenges of controlling nanoporosity precisely. These findings provide guidance for designing thermally efficient, high-reflectivity DBRs for future GaN-based VCSELs.