Fabrication and Characterization of Single-Crystal Diamond Membranes for Quantum Photonics with Tunable Microcavities.

Julia Heupel,Maximilian Pallmann,Rainer Stöhr,Michael Kopnarski,David Hunger,Jonathan Körber,Rolf Merz,Cyril Popov,Johann Peter Reithmaier

doi:10.3390/mi11121080

Abstract

The development of quantum technologies is one of the big challenges in modern research. A crucial component for many applications is an efficient, coherent spin–photon interface, and coupling single-color centers in thin diamond membranes to a microcavity is a promising approach. To structure such micrometer thin single-crystal diamond (SCD) membranes with a good quality, it is important to minimize defects originating from polishing or etching procedures. Here, we report on the fabrication of SCD membranes, with various diameters, exhibiting a low surface roughness down to 0.4 nm on a small area scale, by etching through a diamond bulk mask with angled holes. A significant reduction in pits induced by micromasking and polishing damages was accomplished by the application of alternating Ar/Cl2 + O2 dry etching steps. By a variation of etching parameters regarding the Ar/Cl2 step, an enhanced planarization of the surface was obtained, in particular, for surfaces with a higher initial surface roughness of several nanometers. Furthermore, we present the successful bonding of an SCD membrane via van der Waals forces on a cavity mirror and perform finesse measurements which yielded values between 500 and 5000, depending on the position and hence on the membrane thickness. Our results are promising for, e.g., an efficient spin–photon interface.

Highlights

In recent years, single-crystal diamond (SCD) membranes have emerged as a highly promising platform for various application fields including photonic integrated devices [1,2,3], radiation and pressure sensing [4,5] and nanoelectronics [6,7] due to diamond’s exceptional electrical [8,9,10] and optical properties [11,12]
We present the successful bonding of an SCD membrane via van der Waals forces on a cavity mirror and perform finesse measurements which yielded values between 500 and 5000, depending on the position and on the membrane thickness
We present an approach for fabrication of thin SCD membranes with a thickness in the range of 2–5 μm, utilizing a diamond bulk mask with angled holes to withstand long etch procedures

Summary

Introduction

Single-crystal diamond (SCD) membranes have emerged as a highly promising platform for various application fields including photonic integrated devices [1,2,3], radiation and pressure sensing [4,5] and nanoelectronics [6,7] due to diamond’s exceptional electrical [8,9,10] and optical properties [11,12]. A long coherence time for these defect related electronic states is facilitated by the wide-bandgap material (≈5.5 eV for bulk diamond), since diamond crystals are relatively free of background nuclear spins and feature a low electron concentration as well as low phonon scattering rate [21,22] These color centers, such as the nitrogen-vacancy (NV) center [23,24], the silicon-vacancy (SiV) center [25,26] or the germanium-vacancy center (GeV) [27,28], exhibit a high photostability at room temperature, polarizability and allow a practicable control of coherent single spins, serving as single-photon emitters. The most promising approach is to use minimally processed diamond membranes with a thickness of a few micrometers where color centers remain far away from surfaces, which are introduced into open-access microcavities by bonding to one of the cavity mirrors [25,26,36]. Due to particles on the surface, e.g., originating from the polishing procedure or sputtered material during the reactive ion etching (RIE) process, holes or etch pits can be formed at the surface [24]

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Results

Conclusion