Nitrides Seminar - Special Guests, Marcin Gebsky and Michał Wasiak from Lodz University, Poland
2/12/2019 12PM Elings Hall 1605
1) Monolithic High-Contrast Grating as a versatile mirror for novel VCSEL designs
Monolithic high-contrast grating (MHCG) is a subwavelength diffraction grating characterized by a large polarization discrimination and wavelength-comparable thickness. It can be designed in such a way that it reflects almost 100% of the incident light. Unlike the standard high-contrast grating (HCG), the MHCG doesn’t have to be surrounded by a low refractive index material and hence it can be used as a mirror monolithically integrated with a vertical-cavity surface-emitting laser (VCSEL).
In our presentation we will show experimental results of the first electrically-injected VCSEL incorporating a MHCG mirror made of GaAs. We will discuss a possible design of a GaN VCSEL using GaN MHCG mirrors instead of DBR mirrors. Moreover, we will present a novel metallized MHCG design which might act as both a mirror and an electrical contact in GaN VCSELs.
2) Numerical simulations of tunnel-junction ion-implanted nitride Vertical-Cavity Surface-Emitting Lasers
Vertical-Cavity Surface-Emitting Lasers (VCSELs) have many advantages that make them, in many applications, more suitable than the edge-emitters. Unlike their GaAs-based counterparts, nitride VCSELs have not yet reached the stage of development that allows for wide-spread commercial applications. In the nitride technology there are at least two severe problems: the lack of native lattice-matched Distributed Bragg Reflectors (DBRs), and the lack of high-conductivity p-type material. The former can be addressed by application of dielectric DBRs (although the device’s thermal resistance is deteriorated). A tunnel-junction (TJ) can be used to get around the latter problem.
Simulations performed by the Photonics Group, Lodz University of Technology, concern possible optimizations of TJ, ion-implanted nitride VCSELs with dielectric DBRs. In our talk we will focus on the apparently significant negative impact of the optical absorption in the highly-doped n-GaN contact layers and in the Ta2O5 DBR layers. We will show possible modifications of the structure that help to diminish this problem, and how much, in terms of the optical power emitted by the laser, one can gain.