Rapid Growth of Single Crystal Diamond at High Energy Density by Plasma Focusing

doi:10.15541/jim20220633

Abstract

Abstract:

Single crystal diamond is a kind of crystal material with excellent performance, which has important application value in advanced scientific field. In the field of single crystal diamond growth by microwave plasma chemical vapor deposition (MPCVD), improvement of crystal growth rate is still a key challenge, although corrent high energy density plasma has been a ralatively effective method. In this work, a special plasma focusing structure was designed through magnetohydrodynamic (MHD) model simulation which then was used in the growth experiment based on the simulation. The plasma properties were studied by means of spectral analysis and plasma imaging, and late on single crystal diamond samples were synthesized. The simulation results show that the core electric field and electron density under focusing conditions were 2 times higher than those under normal conditions. The growth experiment results show that plasma with high energy density (793.7 W/cm³) is obtained under conventional microwave power (3500 W) and growth pressure (18 kPa), which is consistent with the model calculation results. We find that a certain amount of nitrogen instead of high energy density growth conditions can significantly change the growth morphology and affect the quality of the crystal. With those findings, we realize the growth rate of single crystal diamond up to 97.5 μm/h. Different from the way to obtain high energy density by increasing the growth pressure, single crystal diamond can be synthesized with high energy density under normal growth pressure and microwave power.

Key words: MPCVD single crystal diamond growth, high energy density, high growth rate, plasma simulation

CLC Number:

TQ174

LI Yicun, LIU Xuedong, HAO Xiaobin, DAI Bing, LYU Jilei, ZHU Jiaqi. Rapid Growth of Single Crystal Diamond at High Energy Density by Plasma Focusing[J]. Journal of Inorganic Materials, 2023, 38(3): 303-309.

Figures/Tables 8

Table 1 Conditions for the growth experiment of single crystal diamond samples

Sample	Substrate type	N₂ concentration/ (μL·L^-1)	Growth rate/ (μm·h^-1)
S1	molybdenum disk	0	9.5
S2	focusing structure	0	32.2
S3	molybdenum disk	300	20.1
S4	focusing structure	300	97.5

Fig. 1 Simulation results of the distribution of electric field and electron density in the reaction chamber at 3500 W and 18 kPa (a) Electric field distribution with molybdenum disk; (b) Electric field distribution with focusing structure; (c) Electron density distribution with molybdenum disk; (d) Electron density distribution with focusing structure

Fig. 2 Observation maps of plasma under two conditions (MW power 3500 W, pressure 18 kPa, with Hα filter) (a, b) Molybdenum disk condition; (c, d) Focusing structure condition; (a, c) are the light intensity contour plots of observation maps (b, d)

Fig. 3 Hα (656 nm) intensity of plasma under different power and pressure conditions Data points in the horizontal axis represent different power-pressure parameters. Data point 1 is the initial parameter (900 W-5 kPa), and then the power and pressure of each data point increase by 200 W and 1 kPa successively until the final growth conditions (3500 W-18 kPa)

Fig. 4 Photos of growth of samples (a) S1 (molybdenum disk); (b) S2 (focusing structure); The growth of S3 and S4 samples is similar

Fig. 5 OE spectra during growth of different samples (a) OE spectra of sample S1, S2, S3 and S4 during the growth experiments; (b) Magnified OE spectra around the CN (388 nm) band; 1 ppm=1 μL/L; Colorful figures are available on website

Fig. 6 Optical microscopic images of surface morphologies of sample after growth (a) S1; (b) S2; (c) S3; (d) S4

Fig. 7 Central region Raman spectra of sample S1, S2, S3, S4 after growth (excited by 532 nm wavelength laser)

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