Fabrication of GaN/AlGaN 1D photonic crystals designed for nonlinear optical applications

TL;DR

This paper reports a reliable fabrication process for GaN/AlGaN 1D photonic crystal microcavities with nonlinear optical properties, enabling efficient frequency conversion for optical applications.

Contribution

It introduces a novel fabrication method combining high-resolution e-beam writing and deep etching for GaN/AlGaN 1D photonic crystals with optimized nonlinear optical features.

Findings

Successful fabrication of deeply etched, high-quality 1D photonic crystal microcavities.

Achieved well-controlled grating periods of 150 nm, 230 nm, and 400 nm.

Demonstrated potential for efficient nonlinear optical frequency conversion.

Abstract

In this paper we present a reliable process to fabricate GaN/AlGaN one dimensional photonic crystal (1D-PhC) microcavities with nonlinear optical properties. We used a heterostructure with a GaN layer embedded between two Distributed Bragg Reflectors consisting of AlGaN/GaN multilayers, on sapphire substrate, designed to generate a {\lambda}= 800 nm frequency down-converted signal (\chi^(2) effect) from an incident pump signal at {\lambda}= 400 nm. The heterostructure was epitaxially grown by metal organic chemical vapour deposition (MOCVD) and integrates a properly designed 1D-PhC grating, which amplifies the signal by exploiting the double effect of cavity resonance and non linear GaN enhancement. The integrated 1D-PhC microcavity was fabricate combing a high resolution e-beam writing with a deep etching technique. For the pattern transfer we used ~ 170 nm layer Cr metal etch mask obtained by means of high quality lift-off technique based on the use of bi-layer resist (PMMA/MMA). At the same time, plasma conditions have been optimized in order to achieve deeply etched structures (depth over 1 micron) with a good verticality of the sidewalls (very close to 90{\deg}). Gratings with well controlled sizes (periods of 150 nm, 230 nm and 400 nm respectively) were achieved after the pattern is transferred to the GaN/AlGaN heterostructure.