Preparation and Hydrogenation Treatment of Single-Crystal Diamond with Different Orientations

doi:10.16553/j.cnki.issn1000-985x.2025.0113

Abstract

Abstract: As a typical ultra-wide bandgap semiconductor material， diamond possesses a bandgap of 5.47 eV， high breakdown electric field， and excellent thermal transport properties， making it highly promising for high-temperature， high-frequency， and high-power electronic devices. Hydrogen-terminated diamond field-effect transistors （FETs） have emerged as a frontier in microelectronics. However， diamond properties exhibit remarkable anisotropy due to varying atomic arrangements and chemical bond distributions across crystal orientations. Most existing studies focus on the （100） plane， while systematic investigations on the （110） and （111） planes （e.g.， processing characteristics and hydrogenation-induced electrical performance） remain insufficient， hindering the development of high-performance diamond devices.This study aims to address the above gap by clarifying differences in processing performance， surface quality， and post-hydrogenation electrical properties among （100），（110） and （111） diamond planes， thereby providing theoretical and experimental foundations for crystal plane selection in diamond device fabrication.In this study， single-crystal diamond was grown by microwave plasma chemical vapor deposition （MPCVD） technology， and diamond wafers with （100），（110） and （111） crystal planes were obtained through laser cutting， with the deviation of crystal plane orientation controlled within 1.2°. Hydroxyl plasma etching was used to observe surface morphologies. An improved dynamic friction polishing （DFP） method—innovatively adopting vacuum adsorption to fix samples （enhancing polishing uniformity） was employed to study the effect of load on material removal rate （MRR） and surface roughness. The high-resolution X-ray diffractometer was employed to determine the crystal orientation deviation of the diamond， the emission scanning electron microscope was used to observe the etched morphologies of the samples and the optical profiler was adopted to characterize the surface roughness of the samples. After hydrogenation， Raman spectroscopy， photoluminescence （PL） spectroscopy， and Hall effect measurements characterized crystal quality and electrical properties.Comparative analysis from the aspects of material processing and hydrogenation treatment reveals that： in hydrogen-oxygen plasma etching， the （100） crystal plane exhibits square etching pits， the （110） crystal plane forms tetrahedral hill-like morphologies， and the （111） crystal plane shows triangular etching pits. Raman and photoluminescence spectra indicate that the samples with different crystal planes exhibit uniform quality and low stress. Polishing experiments indicate that the material removal rate increases with the increment of load. Under a load of 2.0 N/mm²， the polishing removal rate of the （100） crystal plane is 1.1 times that of the （110） crystal plane and 17.7 times that of the （111） crystal plane. The surface roughness first decreases and then increases with the increment of load. When the load is 1.5 N/mm²， the roughness of the （111） crystal plane is as low as 0.118 nm， significantly better than that of the （100） plane （0.934 nm） and the （110） plane （0.708 nm）. Studies have shown that under specific hydrogenation processes， reducing the surface roughness of the samples helps to improve their hydrogenation performance. The （100） crystal plane has higher carrier mobility（103 cm²·V^-1·s^-1）， while the （111） crystal plane exhibits higher carrier concentration （1.25×10¹³ cm^-2） and lower sheet resistance （4 400 Ω/sq）. The （111） crystal plane may be more favorable for fabricating high-performance devices.

Key words: diamond; MPCVD; laser cutting; crystallographic orientation; polishing removal rate; surface roughness; hydrogenation treatment

CLC Number:

O786

LIU Xiaochen, JIANG Long, ZHANG Xin, GE Xingang, LI Yifeng, AN Xiaoming, GUO Hui, SUN Zhenlu, ZHANG Lihui. Preparation and Hydrogenation Treatment of Single-Crystal Diamond with Different Orientations[J]. Journal of Synthetic Crystals, 2025, 54(11): 1907-1915.

Figures/Tables 14

Fig.1 Positional relationship between different crystallographic orientations

Fig.2 As-grown bulk materials （a） and samples with different crystal plane orientations obtained by laser cutting （b）

Fig.3 Schematic diagram of vacuum adsorption DFP

Table 1 Polishing parameters and results of diamond with different crystal faces

Sample	Crystal orientation	Load/（N·mm^-2）	Removed thickness/μm	Polishing time/min	Removal rate/（μm·min^-1）	Surface roughness/nm
1	（100）	1.0	34	28	1.21	1.365
2	（110）	1.0	30	30	1.00	0.937
3	（111）	1.0	28	467	0.06	0.472
4	（100）	1.5	30	19	1.58	0.934
5	（110）	1.5	34	18	1.46	0.708
6	（111）	1.5	26	325	0.08	0.118
7	（100）	2.0	35	18	1.94	1.414
8	（110）	2.0	32	18	1.77	1.632
9	（111）	2.0	25	227	0.11	0.260

Fig.4 The van der Pauw Hall measurement pattern of the hydrogen-terminated diamond

Table 2 Deviation between actual crystal faces and ideal crystal faces

Sample	Crystal orientation	Standard Bragg angle， θ₀/（º）	Actual Bragg angle， θ₁/（º）	Orientation deviation/（º）
1	（100）	59.75	59.23	0.52
2	（110）	37.69	36.84	0.85
3	（111）	21.97	20.85	1.12

Fig.5 Etching morphologies of diamond with different crystal planes

Fig.6 Raman and PL spectra of the diamond plates with different surface orientations

Fig.7 Surface scanning of intrinsic Raman peak positions for diamond with different crystal planes

Fig.8 Polishing removal rate of samples with different crystal planes under different loads

Fig.9 Surface roughness of diamond with different crystal planes under different loads

Fig.10 Morphological characteristics of surface roughness for different crystal planes

Table 3 Room temperature Hall measurement results of diamonds

Sample	Crystal orientation	Surface roughness/nm	Carrier surface density，N_s/cm^-2	Mobility，μ/（cm²·V^-1·s^-1）	Square resistance，R_sh/（Ω·sq^-1）
1	（100）	0.934	1.08×10¹³	103.0	5 800
2	（100）	1.365	1.07×10¹³	102.5	5 860
3	（100）	1.414	1.03×10¹³	100.0	5 920
4	（110）	0.708	1.12×10¹³	102.4	5 260
5	（110）	0.937	1.07×10¹³	102.3	5 320
6	（110）	1.632	1.15×10¹³	99.6	5 360
7	（111）	0.118	1.25×10¹³	101.0	4 440
8	（111）	0.260	1.23×10¹³	100.8	4 460
9	（111）	0.472	1.21×10¹³	100.6	4 510

Fig.11 Electrical properties for diamond with different crystal planes vary with surface roughness

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