RESEARCH ARTICLE Copyright © 2014 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoelectronics and Optoelectronics Vol. 9, 1–5, 2014 Photonic Crystal Structures Based on GaN Ultrathin Membranes Olesea Volciuc 1 2 ∗ , Vladimir Sergentu 3 , Ion Tiginyanu 2 4 ∗ , Marco Schowalter 1 , Veaceslav Ursaki 4 , Andreas Rosenauer 1 , Detlef Hommel 1 , and Jürgen Gutowski 1 1 Institute of Solid State Physics, University of Bremen, Bremen 28334, Germany 2 National Center for Materials Study and Testing, Technical University of Moldova, Chisinau 2004, Moldova 3 Institute of Applied Physics, Academy of Sciences of Moldova, Chisinau 2028, Moldova 4 Institute of Electronic Engineering and Nanotechnologies, Academy of Sciences of Moldova, Chisinau 2028, Moldova We report on maskless fabrication of ultrathin (d ∼ 15 nm) nanoperforated GaN membranes exhibit- ing a triangular lattice arrangement of holes with a diameter of 150 nm, and show that these mem- branes represent an intermediate case between two-dimensional (2D) and three-dimensional (3D) photonic crystals (PhC). A calculation of the dispersion law in the approximation of scalar waves is indicative of the occurrence of surface and bulk modes, further, there is a range of frequencies where only surface modes can exist. Advantages of the occurrence of two types of modes in ultra- thin nanoperforated GaN membranes from the point of view of their incorporation in photonic and optoelectronic integrated circuits are discussed. Keywords: Photonic Crystals, GaN Ultrathin Membranes, Nanostructure Fabrication, Theory and Design. 1. INTRODUCTION Photonic crystal structures based on GaN, as an emer- gent field of applications, widen the traditional applica- tions of GaN and related materials restricted mainly to short-wavelength light-emitting devices and heterostruc- ture field-effect transistors for high-frequency/high-power applications. 1 In particular, one-dimensional photonic crystal (1D-PhC) GaN/AlGaN microcavities have been designed for nonlinear optical applications in integrated photonics. 2 Two-dimensional photonic crystals (2D-PhC) are widely used to address the issue of light extraction for achieving large external quantum efficiency in GaN- based LEDs. The goal in this case is to overcome the total internal reflection at the interface between a LED device and air, which originates from the large difference in the refractive indices between GaN and air. 3–5 Besides that, recent works on photonic crystal resonators have demon- strated the potential of these structures to achieve optical modes with high quality factor (Q) values within small modal volumes, allowing for the occurrence of interesting phenomena such as the Purcell effect, strong coupling, and low-threshold lasing. 6 7 Nitride-based high-quality photonic crystal membranes, however, are not easy to fabricate since the chemical ∗ Authors to whom correspondence should be addressed. inertness of III-N materials makes their processing diffi- cult. Moreover, photonic crystal structures optically active at short wavelengths require a rather small lattice constant, typically between 100 and 200 nm, and transverse sizes of holes between 50 and 150 nm. 6 The realization of reli- able ultrathin GaN membranes with designable nanoarchi- tecture still remains a major technological challenge. Due to the high chemical stability of GaN, its nanostructur- ing is usually based on inductively coupled plasma reac- tive ion etching (ICP-RIE) through lithographically opened windows. 8 9 Electron beam lithography and dry etching techniques including focused-ion beam milling employed to pattern the GaN layer and to fabricate suspended thin membranes through wet etching of sacrificial films are rather expensive, and are generally not suitable for achiev- ing veritable ultrathin membranes. An original method, not based on etching of III-N mate- rials, has been recently proposed for the fabrication of III- nitride photonic crystal membranes. 6 A photonic crystal pattern was first realized in a silicon substrate. GaN quan- tum dots embedded in a thin AlN layer were then grown on top of the patterned silicon substrate, and a free-standing membrane was achieved by selective etching of the silicon substrate through the holes of the photonic crystal. In this paper, we demonstrate the fabrication of GaN PhC ultrathin membranes using a cost-effective technology J. Nanoelectron. Optoelectron. 2014, Vol. 9, No. 2 1555-130X/2014/9/001/005 doi:10.1166/jno.2014.1586 1