Fabrication of thin diamond membranes for photonic applications

Abstract

High quality, thin diamond membranes containing nitrogen-vacancy centers provide critical advantages in the fabrication of diamond-based structures for a variety of applications, including wide field magnetometry, photonics and bio-sensing. In this work we describe, in detail, the generation of thin, optically-active diamond membranes by means of ion implantation and overgrowth. To establish the suitability of our method for photonic applications, photonic crystal cavities with quality factor of 1000 are fabricated. IntroductionNitrogen-vacancy (NV) centers in diamond have emerged as one of the most promising solid state qubits due to their room temperature operation, long spin coherence times, and suitability for optical initialization and readout [1][2][3][4][5][6]. Beyond their quantum photonic applications, NV centers in diamond have been recently utilized to demonstrate electric and magnetic field sensing with exceptional sensitivity and spatial resolution [7][8][9][10]. Furthermore, the bio-compatibility and the chemical inertness of diamond enable applications of NVs in diamond as biosensors for cellular and neural activities [11][12][13]. Many applications in the field of photonic technologies and bio-sensing require availability of high quality, thin diamond membranes with stable NV centers. For instance, coupling single emitters to photonic crystal cavities (PCCs) or waveguides requires thin (~ 300 nm) diamond membranes having only a few NV centers. [14,15] Alternatively, recent schemes for ensemble magnetometry demand high concentrations of NV centers in a free-standing, single crystal diamond slab [10,16]. Thin diamond membranes with diluted NV centers provide an excellent platform for the formation of optical cavities, strongly coupled to single emitters. Several approaches have been utilized to form free-standing diamond membranes from bulk single-crystal diamond. One approach involves high energy (∼ a few MeV) and high dose ion implantation (∼ 1×10 17 ions/cm 2 ) to selectively damage a portion of the diamond, sub-surface, followed by a lift-off of the membrane [17]. Other approaches employ focused ion beam (FIB) milling to etch or 'cut out' suspended diamond membranes [18,19] and vertical etch of diamond substrates [20]. Unfortunately, in both cases, the process of creating the membrane introduces ion damage that degrades the optical performance of the NVs within the membrane. In addition, a residual built-in strain, resulting from the high ion damage, makes subsequent processing of the membranes extremely challenging [21]. Recently, our group demonstrated that an overgrowth method dramatically improves the optical properties of the membranes, making them suitable for device engineering [22,23]. Subsequent reports have shown that a short overgrowth of diamond

Diamond Nanophotonics

“…To achieve full suspension, one option is using Polymethyl methacrylate (PMMA) as a sacrificial layer between the diamond and the SiO 2 . Upon the completion of the devices fabrication, the PMMA can be selectively etched away, leaving behind a suspended photonic crystal [123] . Alternatively, a diamond membrane can be positioned on silicon, and upon patterning the diamond resonator, the silicon material from beneath the devices can be removed with an isotropic etch recipe for Si in a RIE [40,122] .…”

“…While the first experiments of δ − doped films used a bulk crystal, growth on membranes is currently underway. [123,130] …”

Superconducting single-photon detectors integrated with diamond nanophotonic circuits

“…Therefore transferring our approach to single crystal diamond-oninsulator substrates is possible. Recent progress in realizing single crystalline DOI templates via transfer techniques provide promising steps in this direction [48][49][50] . For compatibility with our waferscale fabrication approach, however, here we restrict our work to high quality microcrystalline diamond thin films.…”

High quality-factor optical nanocavities in bulk single-crystal diamond

“…Despite wafer-scale polycrystalline diamond thin films on foreign substrates being readily available, these films typically exhibit inferior properties due to scattering and absorption losses at grain boundaries, significant surface roughness and large interfacial stresses [2][3][4] . In the absence of suitable heteroepitaxial diamond growth, substantial efforts by the diamond photonics and quantum optics community have focused on novel processing techniques to yield nanoscale singlecrystal diamond optical elements [5][6][7][8][9][10][11] . For the most part, these efforts have involved heterogeneous integration of single-crystal diamond slabs (B5-to 30-mm thick) on supporting silica substrates, with subsequent oxygen plasma etching to thin the slab near a target thickness B500-nm or less.…”