Expansion Growth of <110>-oriented Single Crystal Diamond
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The morphology and quality characterization：Expansion Growth of <110>-oriented Single Crystal Diamond
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The substrates used in the experiment are five 5 mm × 5 mm × 0.5 mm high-temperature high-pressure (HTHP) Ib single crystal diamond plates, and they have (110) top and bottom surfaces with two (110) side faces and two (100) side faces . Before the experiment, the top growth surface of the substrates were finely polished. Atomic Force Microscopy (AFM) test results showed a typical polished surface roughness (Ra) of 0.91 nm within 10µm×10µm area . The substrate was then ultrasonically cleaned in acetone, anhydrous ethanol, and deionized water for 15 minutes each to obtain a clean surface. A MPCVD system (Shanghai Platinum World Optoelectronics Technology Co., Ltd.) with a 2.45 GHz, 6 kW microwave power source was used for the diamond epitaxial growth. The purity of the hydrogen and the methane gas source is 6N and 5N5, respectively. Before growth, the MPCVD system was evacuated to below 1×10⁻² Torr to ensure that the chamber was clean and would not introduce impurities during the deposition process. Then, the microwave power and chamber pressure were increased to elevate the temperature on the sample surface to 900oC. The sample surfaces were etched for 10 minutes using a hydrogen flow rate of 300 sccm and an oxygen flow rate of 5 sccm to remove impurities and mechanical damage caused by the surface polishing process, thereby improving the epi-crystal quality. To explore the effect of methane concentration on growth, the sample surface temperature, microwave power, pressure, and growth time were kept constant at 900 °C, 4000 W, 140 Torr, and five hours, respectively. Growth was conducted at CH4/H2 = 2%, 4%, and 6%, and the resulting diamond samples were signed as S1 to S3. The sample for growth at CH4/H2 = 4% and O2/H2 = 0.5% was signed as S4. During the growth, the HR4PRO Spectrometer from Ocean Optics was used to test the plasma species. After growth, the diamond samples were observed using Scanning Electron Microscope (SEM) (ZEISS sigma 300) and AFM (Park Systems NX20) to observe the surface morphology. X-ray diffraction (XRD) (Malvern Panalytical B.V. X' Pert3 MRD), Raman and Photoluminescence (PL) (WITec alpha300RS) were used to analyze the crystal orientation, stress and crystalline quality. All tests were conducted at room temperature.