Diamond films obtained on silicone substrates by the CVD method and properties of structures based on them
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2023-06-01 |
| Journal | Physical Sciences and Technology |
| Authors | А. С. Саидов, Sh. N. Usmonov, Sh. N. Usmonov, U. Kh. Rakhmonov |
| Institutions | Academy of Sciences Republic of Uzbekistan |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”- Novel Buffer Layer Identification: Researchers successfully grew polycrystalline diamond films on n-type Si (111) substrates via Chemical Vapor Deposition (CVD) and identified a previously unreported p(15R-SiC)1-x(Cdiamond)x transition buffer layer formed at the interface.
- High Conductivity: Despite intentional nitrogen doping (via NH3), the resulting diamond films exhibited p-type conductivity with high charge carrier concentrations ((2-4)·1017 cm-3) and high electron mobility (up to 1010 cm2/(V·s)).
- Electroluminescence Demonstrated: The nSi - p(15R-SiC)1-x(Cdiamond)x heterojunction showed a visible whitish-blue electroluminescence glow during reverse bias breakdown (~14-15 V).
- Photon Conversion Mechanism: The structure facilitates the absorption of high-energy, short-wavelength photons (blue-violet) and their re-emission as longer-wavelength photons, which can be absorbed efficiently by the underlying silicon.
- Space Application Potential: This photon conversion and the inherent radiation resistance of diamond make these structures highly promising for enhancing the efficiency and durability of silicon solar cells used in space environments.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Material | Single-crystal Silicon (Si) | N/A | n-type, (111) orientation |
| Substrate Resistivity | ~10 | Ω cm | Initial Si substrate |
| Diamond Film Structure | Polycrystalline | N/A | Fine-grained, continuous film |
| Crystallite Size | 2-3 | µm | Grain size of individual single crystals |
| CVD Filament Temperature | 2100-2150 | °C | During diamond deposition |
| Substrate Temperature | 850-900 | °C | During diamond deposition |
| Average Growth Rate | 0.2-0.3 | µm/h | CVD process rate |
| Total Gas Flow Rate | 50-60 | cm3/min | CH3OH + H2 + NH3 mixture |
| Reactor Pressure | 50-60 | Torr | During deposition |
| H2/Methanol Ratio | 0.5-1.0 | % | In total gas flow |
| Transition Layer Polytype | 15R-SiC | N/A | Forms the p(15R-SiC)1-x(Cdiamond)x solid solution |
| Raman Shift (Diamond Peak) | 1351 | cm-1 | Corresponds to the polycrystalline diamond structure |
| Reverse Breakdown Voltage | ~14-15 | V | nSi - p(15R-SiC)1-x(Cdiamond)x heterojunction |
| Film Conductivity Type | p-type | N/A | Despite nitrogen doping |
| Carrier Concentration | (2-4)·1017 | cm-3 | Measured via Hall method |
| Electron Mobility | 950-1010 | cm2/(V·s) | Measured via Hall method |
Key Methodologies
Section titled “Key Methodologies”- Substrate Selection: Used n-type single-crystal silicon wafers (10x10x0.3 mm) cut in the (111) direction with a specific resistance of ~10 Ω cm.
- Hydrogen Etching Pre-treatment: Silicon surfaces were cleaned immediately prior to epitaxy using hydrogen etching to remove surface SiO2 and create dangling Si bonds.
- Process conditions: 1800 °C filament temperature, 3 min duration, 1000 cm3/min H2 flow.
- Chemical Vapor Deposition (CVD): Diamond films were grown using a well-known CVD technology in a hydrogen-methanol (CH3OH) gas mixture.
- Ammonia (NH3) was added to the mixture to introduce nitrogen impurities, targeting NV center formation.
- Structural Analysis: Film existence and quality were confirmed using microhardness testing, Scanning Electron Microscopy (Jeol JSM-5910LV), and X-ray analysis (JED-2200).
- Raman Spectroscopy: Raman spectra (514 nm laser, 300 K) were used to confirm the polycrystalline diamond structure (peak at 1351 cm-1) and identify the 15R-SiC polytype transition layer.
- Electrical and Optical Characterization: Dark current-voltage characteristics were measured, revealing reverse breakdown at 14-15 V. Electroluminescence was observed during breakdown. Hall measurements determined carrier concentration and mobility.
Commercial Applications
Section titled “Commercial Applications”- Space Photovoltaics: Used as a protective, radiation-resistant coating for silicon solar cells, extending operational life under cosmic radiation.
- Solar Energy Conversion: Functions as an active layer or transparent window that converts high-energy, short-wavelength solar photons into longer-wavelength photons that are more efficiently absorbed by the underlying silicon junction.
- Quantum Computing and Sensing: Nitrogen doping targets the creation of negatively charged Nitrogen-Vacancy (NV-) defects, which are essential components for solid-state qubits and spin detection.
- Optoelectronic Devices: The highly conductive p(15R-SiC)1-x(Cdiamond)x layer can serve as a transparent conductive “window” in micro- and optoelectronic devices, including LEDs and lasers based on NV centers.
- High-Power Electronics: Diamond’s wide bandgap and high thermal conductivity make it suitable for high-voltage and high-temperature diodes, crucial for power electronics operating in extreme conditions.
View Original Abstract
At present, the technology of obtaining diamond films on silicon and other substrates is well studied. However, in all published works to date, there has been no report of a layer of silicon carbide formed between the diamond film and the silicon substrate. The presence of a layer (15R-SiС)1-x(Cdiamond)x in the structure was revealed in the studies of structures with a diamond film obtained by us on silicon substrates by chemical vapor deposition. Diamond films were obtained on single-crystal silicon substrates with (111) orientation and n-type conductivity by the well-known CVD technology in a hydrogen-methanol (CH3OH) mixture with the addition of a certain amount (know-how) of ammonia (NH3). The diamond films consisted of small single crystals 3-5 µm in size, closely interlocked and constituting a continuous film. When studying the current-voltage characteristics of structures created on the basis of the obtained diamond films, a blue-white glow with a blue-violet tint was observed, which is explained by the mixing of blue-violet photons with photons re-emitted in the diamond film.