Date

2017

Document Type

Thesis

Degree

Master of Science

Department

Electrical Engineering

First Adviser

Tansu, Nelson

Abstract

In this thesis, we examine the importance of an efficient mirror in laser structures regarding threshold current density, as well as proposed an alternative reflector in the form of Subwavelength Gratings (SWGs) to standard DBRs for III-Nitride VCSELs. The numerical method Rigorous Coupled Wave Analysis (RCWA) for grating reflectivity is shown and was used in all reflectivity simulations.SWG reflectors for blue light of � = 450 nm capable of ultra-high reflectivity were designed in this work, which is achievable by InGaN quantum well in III-Nitride VCSEL structures. This SWG is a GaN based grating on an air interface with a period (�), of 400 nm, a duty cycle of 50%, and a height (H) of 130 nm which shows reflectivity >99% in the range of � ~400 nm to ~460 nm. This grating is polarization selective and favors reflecting TE light, where the electric field is parallel to the grating bars. The effect of variations in grating period, height, and duty cycle were explored and it was found the period has a significant impact on the position of the reflective band. A threshold analysis was performed on a VCSEL implementing the designed SWG and threshold current densities of ~ 4.6 kA/cm2 were achieved for a light emission of 450 nm. This grating mirror is designed with the intent of replacing the inefficient p-type DBRs in standard III-Nitride VCSEL structures, and was shown to be an exceptional upgrade. Lastly a fabrication for our membrane structure SWG was proposed.

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