  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.
