Dark defect charge dynamics in bulk chemical-vapor-deposition-grown diamonds probed via nitrogen vacancy centers

A. Lozovoi, D. Daw, H. Jayakumar, and C. A. Meriles

Phys. Rev. Materials 4, 053602 – Published 12 May 2020

Abstract

Although chemical vapor deposition (CVD) is one of the preferred routes to synthetic diamond crystals, a full knowledge of the point defects produced during growth is still incomplete. Here we exploit the charge and spin properties of nitrogen vacancy (NV) centers in type-1b CVD diamond to expose an optically and magnetically dark point defect, so far virtually unnoticed despite an abundance comparable to (if not greater than) that of substitutional nitrogen. Indirectly detected photoluminescence spectroscopy indicates a donor state 1.6 eV above the valence band, although the defect's microscopic structure and composition remain elusive. Our results may prove relevant to the growing set of applications that rely on CVD-grown single-crystal diamond.

Received 15 January 2020
Revised 5 April 2020
Accepted 14 April 2020

DOI:https://doi.org/10.1103/PhysRevMaterials.4.053602

Physics Subject Headings (PhySH)

Charge Defects Photoconductivity

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

A. Lozovoi ¹, D. Daw ^1,2, H. Jayakumar¹, and C. A. Meriles^1,2,*

¹Department of Physics, CUNY, The City College of New York, New York, New York 10031, USA
²CUNY Graduate Center, New York, NY 10016, USA

^*cmeriles@ccny.cuny.edu

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Vol. 4, Iss. 5 — May 2020

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Figure 1
(a) DEER pulse sequence adapted to include a variable delay time $τ_{del}$ between the MW1 and MW2 inversion pulses. (b) Measured DEER signal as a function of the MW2 frequency for $τ = 57 μ s$ and $τ_{del} = 0 μ s$ ; the solid line is a calculated spectrum using the known ${}^{14}N$ hyperfine coupling constants at the $N^{0}$ site. (c) Ground-state energy diagram of the $N V^{-}$ and $N^{0}$ centers (left and right respectively) in a magnetic field of 17 mT aligned with the NV symmetry axis; $m_{S}$ ( $m_{S}^{'}$ ) denotes the $N V^{-}$ ( $N^{0}$ ) electron spin projection number and $m_{I}^{'}$ is the ${}^{14}N$ spin projection number at the $N^{0}$ site. (d) DEER signal at 490 MHz as a function of the MW2 pulse duration; all other conditions as in (b). The solid trace is a damped sinusoidal and serves as a guide to the eye. (e) DEER signal (at the $m_{I}^{'} = 0$ transition) as a function of $τ_{del}$ for $τ = 110 μ s$ ; the solid line indicates an exponential fit with a time constant $τ_{dip} = 44 \pm 5 μ s$ corresponding to an $N^{0}$ concentration $n_{N^{0}} = 0.25 \pm 0.03$ ppm. (f) $N V^{-}$ coexist with $N^{0}$ and a dark defect, referred to as X, at least as abundant as nitrogen; see below.
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Figure 2
(a) Adapted DEER sequence for monitoring the N charge state. (b) Normalized DEER contrast as a function of the wait time $τ_{w}$ . The amplitudes are recorded at the $m_{I}^{'} = 0$ transition; all other conditions as in Fig. 2. (c) Schematic energy level diagram. The X acceptor level can be populated either by electron tunneling from neighboring $N^{0}$ or by optical injection of a valence electron.
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Figure 3
(a) Schematics of NV photochromism under optical $(\sim 460 - 637 nm)$ excitation. Steps (1) and (2) describe $N V^{-}$ photoionization into $N V^{0}$ ; steps (3) and (4) correspond to recombination of $N V^{0}$ into $N V^{-}$ . CB (VB) stands for conduction (valence) band. (b) $N V^{0}$ and $N V^{-}$ selective confocal scans (respectively, left and right) upon application of the upper pulse protocol. Zigzags (solid rectangles) indicate a beam scan (park); green (red) color indicates laser excitation at 532 nm (632 nm). We use green (red) laser light for $N V^{0}$ ( $N V^{-}$ ) readout. (c) Same as in (b) but for a red laser park (0.6 mW). In (b) and (c) the park time is 1 min and the scans correspond to $100 \times 100$ pixels and a 10-ms dwell time over a $32 \times 32 - μ m^{2}$ area. (d) $N V^{-}$ photoluminescence as a function of the green laser pulse duration at a point within the $N V^{-}$ -depleted halo; the laser power is 500 µW. (e) Same as in (d) but at the $N V^{-}$ -depleted site created via the protocol in (c).
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Figure 4
(a) We use a protocol identical to that of Fig. 1 but park an IR beam of variable wavelength. Top (bottom) panels show the $N V^{-}$ ( $N V^{0}$ ) fluorescence after a 5-s, 20-mW laser park; all other conditions as in Fig. 1. (b) Proposed mechanism of the $N V^{-}$ bleaching involving the promotion of the electron from the valence band into defect X and capture of the created hole by $N V^{-}$ . (c) Integrated $N V^{-}$ photoluminescence in a 2.8 $\times$ 2.8 μm around the point of illumination as a function of the illumination wavelength. Dashed lines are guides to the eye. (d) Decay rate of the $N V^{-}$ fluorescence under 710-nm illumination as a function of the illumination power; the red line is a linear fit. (e) Fourier-transformed infrared absorbance spectrum.
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