Piezospectroscopy and first-principles calculations of the nitrogen-vacancy center in gallium arsenide

At a Glance

Metadata	Details
Publication Date	2018-01-31
Journal	Journal of Applied Physics
Authors	Nicola Kovač, Christopher Künneth, Hans Christian Alt
Institutions	Munich University of Applied Sciences
Citations	1
Analysis	Full AI Review Included

Technical Analysis: Piezospectroscopy of the Nitrogen-Vacancy Center in Gallium Arsenide (GaAs)

This document analyzes the research detailing the atomic structure, energetics, and vibrational properties of the Nitrogen-Vacancy (NV) center in GaAs, providing technical specifications and linking the required high-precision material characteristics to 6CCVD’s capabilities in high-purity MPCVD diamond materials.

Executive Summary

The investigated paper utilizes high-resolution Fourier Transform Infrared (FTIR) piezospectroscopy and Density Functional Theory (DFT) to characterize the $\text{N}{\text{As}}\text{-}\text{V}{\text{Ga}}$ nearest-neighbor pair (NV center) in bulk GaAs crystals. This methodology and defect analysis directly inform quantum defect engineering in diamond, 6CCVD’s specialty.

Defect Identification: Confirmed the $638 \text{ cm}^{-1}$ local vibrational mode (LVM) originates from the $\text{N}{\text{As}}\text{-}\text{V}{\text{Ga}}$ complex, structurally analogous to the critical NV center in diamond.
Symmetry Confirmation: Experimental piezospectroscopic results under [100] stress, combined with DFT calculations, confirm the trigonal $\text{C}_{3v}$ point symmetry of the relaxed defect.
Charge State Determination: DFT calculations show the $\text{-}3$ charge state is the most thermodynamically stable configuration across nearly all Fermi level positions.
High-Resolution Analysis: Achieved ultra-high-resolution separation of the LVM into four components due to the isotopic perturbation from neighboring $\text{}^{69}\text{Ga}$ and $\text{}^{71}\text{Ga}$ host atoms.
Strain/Field Coupling: Observed and successfully modeled complex non-linear frequency shifts under stress, caused by the coupling between the strain splitting and the intrinsic isotopic anisotropy.
Relevance to Diamond: The principles of defect creation, strain engineering (piezospectroscopy), and $\text{C}_{3v}$ symmetry analysis are directly transferable to the optimization of NV and SiV centers in Single Crystal Diamond (SCD) for quantum applications.

Technical Specifications

The following hard data points were extracted from the experimental results and computational modeling:

Parameter	Value	Unit	Context
N-Vacancy LVM Frequency (Transverse Mode)	638	$\text{cm}^{-1}$	Main FTIR absorption band in GaAs at 10 K
Isotopic Fine Structure Separation	0.24	$\text{cm}^{-1}$	Peak-to-peak separation of $\text{}^{69}\text{Ga}/\text{}^{71}\text{Ga}$ components
FTIR Spectral Resolution (Apodized)	0.08	$\text{cm}^{-1}$	Resolution used for absorption spectra measurement
FWHM (Zero Stress)	0.11 (1)	$\text{cm}^{-1}$	Full Width at Half Maximum of individual LVM components
Maximum Uniaxial Stress Applied ($\sigma$)	0.15	GPa	Applied parallel to the [100] crystallographic direction
Stress-Induced Shift Range (Linear Regime)	0.1 to 0.5	$\text{cm}^{-1}\text{/0.1 GPa}$	Shift magnitude varies between mode components
Sample Temperature	10	K	Measurement environment (Optical Helium Cryostat)
Stable Charge State (DFT)	$\text{-}3$	$q/e$	Lowest formation energy for most Fermi levels
Relaxed N-Ga Bond Length (DFT)	1.89	$\text{Å}$	Distance supporting the $\text{C}_{3v}$ symmetry
DFT Vibrational Frequency Scaling Factor	0.9862	$\text{-}$	Used to match calculated $\omega_{\text{calc}}$ to experimental $\omega_{\text{exp}}$

Key Methodologies

The study combined high-pressure, low-temperature measurement techniques with sophisticated all-electron DFT modeling.

Material Growth and Preparation:
- Crystal Growth: GaAs bulk crystal grown via the Liquid-Encapsulation Czochralski (LEC) technique.
- Doping Method: Nitrogen doping achieved by applying a $\text{N}_{2}$ gas atmosphere at 70 bar during crystal growth.
- Sample Cutting: Rod-like specimens (2 mm x 4 mm x 10 mm) were cut with the long axis aligned precisely parallel to the [001] direction for uniaxial stress application.
Piezospectroscopy & FTIR Measurement:
- Stress Application: Uniaxial stress (up to 0.15 GPa) applied using a home-made push-rod apparatus within an optical helium cryostat (Sample temperature: 10 K).
- Equipment: FTIR measurements performed using a Bruker Vertex 80v vacuum instrument.
- Detection: Potassium Bromide (KBr) beam splitter and a liquid-nitrogen cooled Mercury Cadmium Telluride (MCT) detector.
- Polarization Control: A wire-grid polarizer was used in front of the cryostat to obtain polarized absorption spectra.
Density Functional Theory (DFT) Modeling:
- Code & Basis: Calculations performed using the all-electron DFT code FHI-Aims, utilizing numeric atom-centered basis functions (Second tier level in LDA approximation).
- Super Cell: A 64-atom ($\text{Ga}{32}\text{As}{32}$) super cell was used, structured as $\text{Ga}{31}\text{As}{31}\text{N}$ with one Ga atom removed ($\text{N}{\text{As}}\text{-}\text{V}{\text{Ga}}$).
- Relaxation: Atomic positions and lattice constants were relaxed until electronic and ionic forces fell below strict limits ($\text{5 x } 10^{-5} \text{ eV/Å}$ for ionic forces).
- Vibrational Frequency Calculation: Used the Phonopy utility coupled with the finite displacements method to derive LVM frequencies and simulate isotopic effects.

6CCVD Solutions & Capabilities

This research paper provides an essential technical roadmap for engineers developing strain-controlled quantum devices. The study of the $\text{C}_{3v}$ symmetric NV center in GaAs, and its manipulation via piezospectroscopy, directly parallels the critical research required to optimize the performance of NV centers in 6CCVD’s Single Crystal Diamond (SCD) for quantum computing and sensing applications.

6CCVD offers the specialized materials and customization services necessary to replicate this methodology for diamond-based research and next-generation device fabrication.

Applicable Materials

The ability to precisely control crystal defect precursors, symmetry, and charge state is paramount to extending this research into functional quantum devices.

Material Recommendation	Application in Quantum Defect Engineering	6CCVD Capability Match
Optical Grade Single Crystal Diamond (SCD)	The fundamental host material for high-coherence NV centers. Required for low background absorption essential for FTIR and optical measurements.	SCD Thickness: $0.1 \text{ µm} \text{ - } 500 \text{ µm}$. Custom Wafers up to 125 mm.
Boron-Doped Diamond (BDD)	Used to precisely control the Fermi level, allowing stabilization of specific NV charge states ($\text{NV}^{0}$ or $\text{NV}^{-}$), analogous to the preferred $\text{-}3$ state observed in the GaAs study.	Customizable doping levels (lightly to heavily BDD).
Polycrystalline Diamond (PCD)	Suitable for large-area diamond anvil cell (DAC) applications where extreme pressure/stress must be applied for material characterization.	Inch-size PCD wafers; Surface roughness $\text{Ra } < 5 \text{ nm}$.

Customization Potential

The experimental success depends on meticulously prepared, precisely oriented samples subjected to controlled strain, requiring advanced fabrication capabilities.

Service	Requirement Identified in Research	6CCVD Custom Solution
Precision Polishing (Ra)	Critical for reducing scattering losses during high-resolution FTIR and photoluminescence studies.	Standard polishing achieving $\text{Ra } < 1 \text{ nm}$ on SCD; suitable for high-fidelity optical studies.
Custom Crystal Orientation	Paper required precise [001] alignment for uniaxial stress. Diamond research demands precise [100] or [111] alignment for NV center spin quantization.	SCD wafers provided with certified crystallographic orientation (e.g., [100], [111]) to maximize strain alignment and defect coherence.
Advanced Metalization	Required for creating electrodes or integrated stress gauges for high-precision piezospectroscopic setups.	In-house multi-layer metalization using Au, Pt, Pd, Ti, W, Cu, tailored for adhesion, ohmic contact, and subsequent bonding.
Custom Dimensions & Shaping	The paper used specific 2 mm x 4 mm x 10 mm rods for stress analysis.	High-precision laser cutting and shaping services to produce rods, cantilevers, or custom device geometries.

Engineering Support

The analytical approach demonstrated in this paper—linking applied strain fields to fundamental defect symmetry ($\text{C}_{3v}$) and LVM spectroscopy—is core to 6CCVD’s material science focus.

6CCVD’s in-house PhD engineering team specializes in the growth and characterization of diamond materials optimized for quantum applications. We offer comprehensive consultation on material selection, defect incorporation (e.g., nitrogen/silicon precursors), and substrate preparation for projects involving:

Piezospectroscopy and Strain Engineering for modifying spin resonance frequencies (e.g., $\text{NV}^{-}$ center).
High-Resolution LVM Analysis for precursor identification and defect quantification.
Controlling Charge State Stability through customized Boron doping to ensure maximum concentration of the desired quantum state.

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

View Original Abstract

The nitrogen-vacancy (NV) center occurs in GaAs bulk crystals doped or implanted with nitrogen. The local vibration of nitrogen gives rise to a sharp infrared absorption band at 638 cm-1, exhibiting a fine structure due to the different masses of neighboring 69Ga and 71Ga host isotopes. Piezospectroscopic investigations in the crystallographic ⟨100⟩ direction prove that the center has C3v point symmetry, which is weakly perturbed by the isotope effect. The stress-induced shifts of some band components show an unusual non-linear behavior that can be explained by coupling between the isotope and the stress splitting. First-principles density-functional theory calculations are in full accordance with the experiments and confirm the C3v symmetry, caused by relaxation of the nitrogen atom from the anion lattice site towards the nearest-neighbor Ga plane. Furthermore, the calculations indicate the -3 charge state of the center as the most stable one for nearly all Fermi level positions. The NV center in GaAs is structurally analogous to the same center in diamond.

Tech Support

Original Source

DOI: https://doi.org/10.1063/1.5011302

References

1985 - Proceedings of the 17th International Conference on the Physics of Semiconductors [Crossref]