Selective Undercut of Undoped Optical Membranes for Spin-Active Color Centers in 4H-SiC

TL;DR

This paper introduces a novel selective photoelectrochemical etching method based on electrical depletion, enabling the fabrication of high-purity undoped SiC membranes that enhance quantum emitter performance.

Contribution

Developed a doping-independent etching process using diode depletion to create undoped SiC membranes for quantum and photonic applications.

Findings

Undoped membranes show >3x longer spin lifetime than doped ones.

The process allows scalable fabrication of high-purity SiC thin films.

Membranes are compatible with quantum emitters for quantum technologies.

Abstract

Silicon carbide (SiC) is a semiconductor used in quantum information processing, microelectromechanical systems, photonics, power electronics, and harsh environment sensors. However, its high temperature stability, high breakdown voltage, wide bandgap, and high mechanical strength are accompanied by a chemical inertness which makes complex micromachining difficult. Photoelectrochemical etching is a simple, rapid means of wet processing SiC, including the use of dopant selective etch stops that take advantage of mature SiC homoepitaxy. However, dopant selective photoelectrochemical etching typically relies on highly doped material, which poses challenges for device applications such as quantum defects and photonics that benefit from low doping to produce robust emitter properties and high optical transparency. In this work, we develop a new, selective photoelectrochemical etching process that relies not on high doping but on the electrical depletion of a fabricated diode structure, allowing the selective etching of an n-doped substrate wafer versus an undoped epitaxial ($N_a=1(10)^{14}cm^{-3}$) device layer. We characterize the photo-response and photoelectrochemical etching behavior of the diode under bias and use those insights to suspend large ($>100\mu m^2$) undoped membranes of SiC. We further characterize the compatibility of membranes with quantum emitters, performing comparative spin spectroscopy between undoped and highly doped membrane structures, finding the use of undoped material improves ensemble spin lifetime by $>3x$. This work enables the fabrication of high-purity suspended thin films suitable for scalable photonics, mechanics, and quantum technologies in SiC.