High-Quality SiO2/O-Terminated Diamond Interface - Band-Gap, Band-Offset and Interfacial Chemistry

At a Glance

Metadata	Details
Publication Date	2022-11-22
Journal	Nanomaterials
Authors	J. Cañas, D.F. Reyes, Alter Zakhtser, Christian Dussarrat, Takashi Teramoto
Institutions	Centre National de la Recherche Scientifique, Institut polytechnique de Grenoble
Citations	8
Analysis	Full AI Review Included

Executive Summary

This research successfully characterizes the high-quality interface formed by Atomic Layer Deposition (ALD) of amorphous silicon oxide (SiO₂) on oxygen-terminated (100) p-type diamond, validating its potential as a gate dielectric for diamond electronics.

Gate Oxide Quality: Amorphous SiO₂ was synthesized successfully via ALD, exhibiting a homogeneous ultra-wide band-gap (E_g) of 9.4 ± 0.2 eV across the layer, confirming its suitability for high-voltage applications.
Band Alignment: A highly favorable straddling band setting was established between SiO₂ and diamond, crucial for minimizing leakage currents in both accumulation and inversion regimes.
High Energy Barriers: Substantial band offsets were measured: a Valence Band Offset (VBO) of 2.0 eV and a Conduction Band Offset (CBO) of 1.9 eV. These barriers are significantly higher than those reported for other oxides on diamond.
Interfacial Chemistry: The interface bonding is dominated by single- and double-carbon-oxygen (C-O, C=O) bonds, with a scarce presence of silicon-carbon (C-Si) bonds, correlating with the previously reported low density of interface states.
Device Potential: The combination of wide band-gap, high band offsets, and low interface state density opens the route for fabricating stable, high-power diamond MOSFETs, including inversion-based devices requiring a large electron barrier.

Technical Specifications

Parameter	Value	Unit	Context
Diamond Type	p-type (100) CVD	-	O-terminated surface
Nominal Boron Conc.	~10¹⁶	cm^-3	Doping level of the active layer
CVD Growth Temperature	900	°C	Epitaxy conditions
CVD Pressure	33	Torr	Epitaxy conditions
SiO₂ Thicknesses	2 and 40	nm	ALD layer thicknesses studied
SiO₂ Phase	Amorphous	-	Confirmed by XPS VB peaks
SiO₂ Band-Gap (VEELS)	9.4 ± 0.2	eV	Bulk measurement (more reliable)
SiO₂ Band-Gap (PEELS)	9.0 ± 0.2	eV	Surface-sensitive measurement
Diamond Band-Gap (E_g)	5.5	eV	Reference value (Figure 5)
Valence Band Offset (VBO)	2.0	eV	Barrier for holes
Conduction Band Offset (CBO)	1.9	eV	Barrier for electrons
Diamond Breakdown Field	Up to 10	MV/cm	Superior material property [1]
Interface Bonding Ratio (C=O)	50	%	Relative area of C(1s) components
Interface Bonding Ratio (C-O)	35	%	Relative area of C(1s) components
Interface Bonding Ratio (C-Si)	15	%	Relative area of C(1s) components

Key Methodologies

The study combined advanced microscopy and spectroscopy techniques to characterize the heterojunction, focusing on precise band-gap and band-offset determination.

Diamond Epitaxy:
- p-type diamond layers (~1 µm thick) were grown via Microwave Plasma Chemical Vapor Deposition (MPCVD) on High Pressure High Temperature (HPHT) Ib substrates.
- Gas mixture included CH₄/H₂ = 1% and O₂/H₂ = 0.25%, with B/C = 60 ppm.
Surface Termination:
- The diamond surface was oxidized using an ozone plasma treatment.
- Conditions: 120 minutes at 500 mbar, utilizing a Xenon EXCIMER UV lamp (172 nm) to achieve O-termination.
Gate Oxide Deposition:
- Silicon oxide (SiO₂) layers (2 nm and 40 nm) were grown using Atomic Layer Deposition (ALD).
Scanning Transmission Electron Microscopy (STEM-EELS):
- Used to determine the bulk band-gap and interfacial chemistry at nanometer resolution.
- VEELS (Valence EELS): Measured the SiO₂ band-gap (9.4 eV). A low accelerating voltage (60 kV) was used to mitigate the Cherenkov effect, ensuring accurate band-gap estimation.
- Interface Analysis: EELS spectra (O K-edge and Si L-edge) confirmed C-O bonding dominance at the interface, with no detectable silicon signal on the diamond side.
X-ray Photoelectron Spectroscopy (XPS):
- Used for precise band alignment and interfacial bond quantification.
- Conditions: High-resolution monochromatic Al-Kα radiation (hν = 1486.7 eV), mild Ar⁺ cleaning (0.5 kV).
- PEELS (Photoelectron EELS): Measured the SiO₂ band-gap (9.0 eV) from the O(1s) core level energy loss spectrum.
- C(1s) Deconvolution: Identified and quantified interfacial bonds: C=O (50%), C-O (35%), and C-Si (15%).
- Band Offset Calculation: VBO and CBO were calculated using the core level and Valence Band Maximum (VBM) data from the 40 nm (bulk) and 2 nm (interface) samples.

Commercial Applications

The successful integration of high-quality SiO₂ as a gate dielectric on O-terminated diamond enables the development of next-generation power and high-frequency electronics.

High-Power Switching Devices:
- Product: Diamond Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs).
- Benefit: Utilizes diamond’s 10 MV/cm breakdown field and the high CBO (1.9 eV) and VBO (2.0 eV) barriers provided by the SiO₂ gate, minimizing leakage and enabling high-voltage operation.
High-Temperature Electronics:
- Industry: Aerospace, Automotive (EV power management), Geothermal Sensing.
- Benefit: O-terminated diamond and SiO₂ are thermally stable (O-termination up to 700 K), allowing device operation in environments exceeding the limits of silicon carbide (SiC) devices.
Normally-Off Transistors:
- Product: Depletion and Inversion-based MOSFETs.
- Benefit: The O-termination naturally depletes holes, facilitating normally-off operation. The large CBO (1.9 eV) is critical for achieving stable inversion regimes, a key requirement for energy-efficient power electronics.
Harsh Environment Systems:
- Industry: Nuclear, Defense, Space.
- Benefit: Diamond’s inherent radiation hardness, combined with a stable, low-defect gate oxide interface, ensures reliability in high-radiation or high-vibration environments.

View Original Abstract

Silicon oxide atomic layer deposition synthesis development over the last few years has open the route to its use as a dielectric within diamond electronics. Its great band-gap makes it a promising material for the fabrication of diamond-metal-oxide field effects transistor gates. Having a sufficiently high barrier both for holes and electrons is mandatory to work in accumulation and inversion regimes without leakage currents, and no other oxide can fulfil this requisite due to the wide diamond band-gap. In this work, the heterojunction of atomic-layer-deposited silicon oxide and (100)-oriented p-type oxygen-terminated diamond is studied using scanning transmission electron microscopy in its energy loss spectroscopy mode and X-ray photoelectron spectroscopy. The amorphous phase of silicon oxide was successfully synthesized with a homogeneous band-gap of 9.4 eV. The interface between the oxide and diamond consisted mainly of single- and double-carbon-oxygen bonds with a low density of interface states and a straddling band setting with a 2.0 eV valence band-offset and 1.9 eV conduction band-offset.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano12234125

References

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