Large-scale GaP-on-diamond integrated photonics platform for NV center-based quantum information

At a Glance

Metadata	Details
Publication Date	2016-01-13
Journal	Journal of the Optical Society of America B
Authors	Michael N. Gould, Srivatsa Chakravarthi, Ian Christen, N. Thomas, Shabnam Dadgostar
Institutions	University of Washington, Humboldt-Universität zu Berlin
Citations	34
Analysis	Full AI Review Included

Technical Documentation & Analysis: GaP-on-Diamond Integrated Photonics for NV Center Quantum Information

This document analyzes the research paper “A Large-Scale GaP-on-Diamond Integrated Photonics Platform for NV Center-Based Quantum Information” to provide technical specifications and demonstrate how 6CCVD’s advanced MPCVD diamond solutions can support and scale this critical quantum technology.

Executive Summary

Scalable Quantum Platform: The research successfully demonstrates a hybrid GaP-on-Diamond integrated photonics platform suitable for Measurement-Based Quantum Computation (MBQC) utilizing Nitrogen-Vacancy (NV) centers.
High Efficiency Projection: The platform achieves a projected Total Quantum Efficiency (TQE) of 33% into an on-chip guided mode, representing a factor of >200 improvement over current free-space collection techniques.
Material System: The system relies on high-quality, electronic-grade Single Crystal Diamond (SCD) substrates hosting near-surface NV centers (~15 nm deep), overlaid with a 125 nm GaP waveguiding layer.
High Component Yield: Demonstrated high yields for key integrated components, including 89% for full measurement loops and 58% for waveguide-coupled disk resonators, confirming the platform’s suitability for complex circuit integration.
Exceptional Quality Factors: Measured intrinsic Quality Factors (Q_i) up to 11,700 in disk resonators, crucial for achieving significant Purcell enhancement (F_p ~24) and efficient ZPL photon emission.
6CCVD Value Proposition: 6CCVD provides the necessary high-purity, electronic-grade SCD substrates with custom dimensions (up to 125 mm) and precision thickness control required to scale this technology from lab prototypes to commercial quantum circuits.

Technical Specifications

The following hard data points were extracted from the analysis of the integrated photonics platform performance:

Parameter	Value	Unit	Context
Diamond Substrate Grade	Electronic Grade	N/A	Commercially sourced SCD
NV Center Depth	~15	nm	Below diamond surface (via implantation/annealing)
GaP Waveguide Thickness	125	nm	Epitaxially grown layer
Diamond Pedestal Etch Depth	600	nm	Etched into the SCD substrate
Resonator Intrinsic Quality Factor (Q_i)	Up to 11,700	N/A	Coupler Type 3 geometry
Resonator Measured Q (Best Device)	5,100	N/A	Used for ZPL photon collection
Projected On-Chip TQE	33	%	Into useful waveguide modes
Projected Off-Chip TQE	5.5	%	Total quantum efficiency (with grating coupler)
ZPL Wavelength	637.2	nm	Zero-Phonon Line
Average Grating Coupler Efficiency	17.0 ± 1.5	%	At ZPL wavelength
Directional Coupler Excess Loss (180 nm ridge)	0.063 ± 0.015	dB/µm	Per unit length
Full Measurement Loop Yield	89	%	97 out of 109 loops working

Key Methodologies

The fabrication process relies heavily on precise material preparation and etching of the diamond substrate:

NV Center Creation: Electronic grade diamond chips (2 mm x 2 mm) were subjected to ion implantation and annealing to create negatively charged NV centers approximately 15 nm below the surface.
Surface Preparation: The diamond was rigorously cleaned using a solution of KNO₃ in fuming H₂SO₄, followed by treatment with hexamethyldisilazane (HMDS) vapor.
GaP Membrane Transfer: A 125 nm thick GaP layer, grown on an Al_0.8Ga_0.2P sacrificial layer, was released via wet etching (1.5% hydrofluoric acid) and transferred to the prepared diamond surface.
Photonic Patterning: Electron-beam lithography was used with hydrogen silsesquioxane (HSQ) negative resist to define the integrated photonic structures.
Substrate Etching (RIE): A two-step Reactive Ion Etch (RIE) was performed:
- Cl₂/N₂/Ar chemistry etched the GaP layer.
- O₂ RIE followed, etching approximately 600 nm into the diamond substrate to form the diamond pedestal supporting the GaP waveguides.
Measurement: Transmission measurements were conducted using a custom microscope setup, coupling light via grating couplers and analyzing output via a spectrometer or photodetector. NV emission was excited using a 532 nm laser at low temperature (T ≈ 7K).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the foundational diamond materials and custom processing required to scale this high-performance GaP-on-Diamond quantum platform.

Applicable Materials

To replicate and extend this research, 6CCVD recommends the following materials:

Optical Grade Single Crystal Diamond (SCD): Required for the substrate, ensuring ultra-low birefringence and high transmission at the ZPL wavelength (637.2 nm). Our SCD offers Ra < 1 nm polishing, critical for minimizing scattering losses at the GaP/Diamond interface.
Electronic Grade SCD Substrates: Essential for hosting high-coherence NV centers. 6CCVD provides high-purity SCD material suitable for subsequent ion implantation and high-temperature annealing protocols.
Custom Thickness Control: We offer SCD wafers with thicknesses ranging from 0.1 µm up to 500 µm, allowing researchers to optimize the starting material for precise near-surface NV placement and deep etching (600 nm pedestal) requirements.

Customization Potential

The complexity of integrated quantum circuits demands highly customized material preparation, which 6CCVD provides:

Research Requirement	6CCVD Customization Service	Benefit to Client
Scaling Chip Dimensions	Large-Area Wafers: We supply SCD plates up to 10 mm thick and Polycrystalline Diamond (PCD) wafers up to 125 mm in diameter.	Enables the transition from 2 mm x 2 mm lab chips to wafer-scale fabrication, maximizing yield and throughput.
Deep Etching into Diamond	Thick Substrates: Provision of robust SCD substrates (up to 10 mm) capable of withstanding the 600 nm RIE pedestal etch and subsequent processing steps.	Ensures mechanical stability and consistency across large-area devices.
Integration of Control Electronics	Custom Metalization: In-house deposition of Au, Pt, Pd, Ti, W, and Cu.	Facilitates the integration of electrodes for Stark tuning (required for dynamic stabilization of optical resonances) and RF antennas for spin manipulation, as noted in the paper’s future work section.
Surface Quality for GaP Transfer	Ultra-Low Roughness Polishing: SCD polishing to Ra < 1 nm.	Minimizes interface defects and scattering losses, which is crucial for maintaining the high Q factors (up to 11,700) demonstrated in the resonators.

Engineering Support

6CCVD’s in-house PhD team can assist with material selection and optimization for similar NV Center-Based Quantum Photonic projects. Our expertise covers:

Substrate Optimization: Consulting on diamond surface termination and cleaning protocols to ensure optimal adhesion and quality for the GaP membrane transfer process.
Defect Engineering: Guidance on selecting the appropriate diamond grade and thickness to maximize NV center yield and coherence time following implantation and annealing.
Process Integration: Support for integrating custom metal layers necessary for electro-optic switching (leveraging GaP’s second-order non-linearity) and RF control elements.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

We present chip-scale transmission measurements for three key components of a\nGaP-on-diamond integrated photonics platform: waveguide-coupled disk\nresonators, directional couplers, and grating couplers. We also present\nproof-of-principle measurements demonstrating nitrogen-vacancy (NV) center\nemission coupled into selected devices. The demonstrated device performance,\nuniformity and yield place the platform in a strong position to realize\nmeasurement-based quantum information protocols utilizing the NV center in\ndiamond.\n

Tech Support

Original Source

DOI: https://doi.org/10.1364/josab.33.000b35