Fabrication of photonic crystal circuits based on GaN ultrathin membranes by maskless lithography

Abstract

We report on maskless fabrication of photonic crystal (PhC) circuits based on ultrathin (d ~ 15 nm) nanoperforated GaN membranes exhibiting a triangular lattice arrangement of holes with diameters of 150 nm. In recent years, we have proposed and developed a cost-effective technology for GaN micro-and nanostructuring, the so-called surface charge lithography (SCL), which opened wide possibilities for a controlled fabrication of GaN ultrathin membranes. SCL is a maskless approach based on direct writing of negative charges on the surface of a semiconductor by a focused ion beam (FIB). These charges shield the material against photo-electrochemical (PEC) etching. Ultrathin GaN membranes suspended on specially designed GaN microstructures have been fabricated using a technological route based on SCL with two selected doses of ion beam treatment. Calculation of the dispersion law in nanoperforated membranes in the approximation of scalar waves is indicative of the occurrence of surface and bulk modes, and there is a range of frequencies where only surface modes can exist. Advantages of the occurrence of two types of modes in ultrathin nanoperforated GaN membranes from the point of view of their incorporation in photonic and optoelectronic integrated circuits are discussed. Along with this, we present the results of a comparative analysis of persistent photoconductivity (PPC) and optical quenching (OQ) effects occurring in continuous and nanoperforated ultrathin GaN suspended membranes, and assess the mechanisms behind these phenomena.

Porous semiconductor compounds

“…While most of the ordered semiconductor nanostructures prepared by electrochemical etching are based on selforganization processes or on using surface charge lithography (as in the case of GaN nanostructures [295,297]), hexagonal close-packed 2D photonic crystals were formed by electrochemical growth of CdSe through the interstitial spaces between polymer nano/micro sphere templates [298]. In such a case, the confocal voids containing photonic crystals can be made either interconnected or well separated, with high uniformity.…”

Atomically thin semiconducting layers and nanomembranes: a review

“…FIB-induced nanoperforation by design of GaN membranes enabled the fabrication of flexible 2D photonic crystals with embedded waveguides, beam splitters, and ring resonators [88][89][90] (see figure 27). Actually, any lattice defect can be routinely designed and realized in the 2D photonic crystals involved.…”

Dose influence on the PMMA e-resist for the development of high-aspect ratio and reproducible sub-micrometric structures by electron beam lithography

“…Nevertheless, it exists also other different techniques for reaching this aim, as, for example, the immersion lithography, able to increase the resolution of classical deep UV lithography down to 20 nm using excimer lasers with wavelengths of 193 and 248 nm [4,5], the nanoimprinting lithography (NIL) that creates patterns by mechanical deformation of imprint resist and subsequent processes [6,7,8], or the Focused Ion Beam (FIB) Lithography [9,10].…”