Electrical Characteristics of Diamond MOSFET with 2DHG on a Heteroepitaxial Diamond Substrate

At a Glance

Metadata	Details
Publication Date	2022-03-31
Journal	Materials
Authors	Genqiang Chen, Wei Wang, Fang Lin, Minghui Zhang, Qiang Wei
Institutions	Hebei Semiconductor Research Institute, Xi’an Jiaotong University
Citations	5
Analysis	Full AI Review Included

Executive Summary

This research successfully demonstrates a high-performance hydrogen-terminated diamond (H-diamond) Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) fabricated on a large-area heteroepitaxial diamond (HSCD) substrate.

Core Achievement: The device performance metrics (current density, transconductance) are achieved on HSCD, proving that this lower-cost, scalable material can compete with traditional, size-limited homoepitaxial diamond for electronic applications.
Peak Performance: The MOSFET achieved a maximum output current density of 172 mA/mm and a peak transconductance of 10.4 mS/mm.
Material Quality: The HSCD substrate exhibited a high crystalline quality, measured by an X-ray rocking curve FWHM of 209.5 arcsec for the diamond (004) peak.
Mobility Enhancement: A low-temperature annealing process (423 K for 3 min in N₂) increased the hole field effective mobility (µ_eff) by 27% (from 36.5 to 46.5 cm²/Vs).
Interface Improvement: The mobility increase was directly correlated with a decrease in the interface state density (D_it), confirming improved ALD-Al₂O₃/H-diamond interface quality after 423 K annealing.
Device Characteristics: The device operates normally-on (V_th = 11.85 V) with a low on-resistance (130.5 Ω·mm) and an on/off ratio greater than 10⁵.

Technical Specifications

Parameter	Value	Unit	Context
Substrate Type	Heteroepitaxial Single Crystal Diamond (HSCD)	N/A	Free-standing, 26 x 26 x 1 mm³
HSCD Quality (FWHM)	209.5	arcsec	Diamond (004) X-ray rocking curve
Gate Length (L_G)	2	µm	Device geometry
Gate Width (W_G)	100	µm	Device geometry
Dielectric Material	ALD-Al₂O₃	N/A	Gate oxide
Dielectric Thickness	30	nm	Total thickness
Max Output Current Density (I_DS)	172	mA/mm	V_GS = -8 V, V_DS = -30 V (As-fabricated)
Max Transconductance (g_m(max))	10.4	mS/mm	As-fabricated
On-Resistance (R_ON)	130.5	Ω·mm	V_GS = -8 V
Threshold Voltage (V_th)	11.85	V	As-fabricated (Normally-on)
Carrier Density (p)	3.3 x 10¹³	cm^-2	At V_GS = -8 V
Effective Mobility (µ_eff)	36.5	cm²/Vs	As-fabricated
Effective Mobility (µ_eff)	46.5	cm²/Vs	Post-annealing (423 K, 3 min)
Mobility Improvement	27	%	After 423 K annealing
Interface State Density (D_it)	1.07 x 10¹³	eV^-1/cm²	As-fabricated
Interface State Density (D_it)	8 x 10¹²	eV^-1/cm²	Post-annealing (423 K, 3 min)
Subthreshold Slope (SS)	400	mV/dec	Minimum value
On/Off Ratio	>10⁵	N/A	Measured at RT

Key Methodologies

The MOSFET fabrication involved several critical steps, focusing on heteroepitaxial growth and precise interface control using Atomic Layer Deposition (ALD).

HSCD Substrate Preparation:
- Initial Substrate: a-plane (11-20) sapphire (26 x 26 x 1 mm³).
- Buffer Layer: Approximately 150 nm Ir deposited at 900 °C via magnetron sputtering.
- Nucleation: Bias Enhanced Nucleation (BEN) conducted in direct current CVD.
- Epitaxial Growth: Horizontal type MPCVD used for 100 h (Growth rate: 10 µm/h).
Homoepitaxial Layer Growth:
- A 100 nm homoepitaxial layer was grown on the HSCD using MPCVD.
- Parameters: Temperature 930-970 °C, Pressure 30 Torr, Time 60 min.
- Gas Flow: H₂ (300 sccm), CH₄ (0.6 sccm).
H-Termination and Ohmic Contact:
- Hydrogen plasma was maintained for 20 min to form the H-diamond surface.
- Source and Drain (S/D) electrodes (200 nm Au) were deposited via electron beam evaporation.
Channel Passivation and Oxidation:
- Ultraviolet Ozone (UV/O₃) was used to convert the H-termination outside the channel region into Oxygen Termination (OT).
Gate Dielectric Deposition (ALD-Al₂O₃):
- Precursor: Trimethylaluminum (TMA) and H₂O.
- Step 1 (Protection): A 5 nm Al₂O₃ layer deposited at 90 °C to protect the C-H bonds from oxidation.
- Step 2 (Dielectric): A 25 nm Al₂O₃ layer deposited at 250 °C.
- Gate Electrode: 30/150 nm Ti/Au deposited on the Al₂O₃ layer.
Annealing Study:
- Samples were annealed in N₂ atmosphere for 3 min at two temperatures: 423 K and 473 K, to study the effect on interface quality and mobility.

Commercial Applications

The successful demonstration of high-performance MOSFETs on scalable heteroepitaxial diamond substrates opens up significant commercial opportunities in fields requiring extreme electronic performance and thermal stability.

High-Power Electronics: Diamond’s high breakdown electrical field (>10 MV/cm) and wide bandgap (5.5 eV) make it ideal for high-voltage switching devices (e.g., in power grids, electric vehicles, and industrial motor drives).
High-Frequency RF Devices: The high carrier mobility (up to 4500 cm²/Vs for electrons and 3800 cm²/Vs for holes) supports applications in high-frequency amplifiers and oscillators, potentially exceeding 100 GHz operation (as previously demonstrated on diamond FETs).
Thermal Management: Diamond’s extremely high thermal conductivity (22 W/cmK) is crucial for managing heat in densely integrated high-power electronic modules, acting as an integrated heat spreader.
Aerospace and Harsh Environments: The robust nature of diamond allows for reliable operation in high-temperature or high-radiation environments where silicon or GaAs devices fail.
Scalable Substrates: The use of heteroepitaxial diamond addresses the cost and size limitations of traditional diamond substrates, enabling mass production of large-area diamond wafers for commercial semiconductor manufacturing.

View Original Abstract

In this work, hydrogen-terminated diamond (H-diamond) metal-oxide-semiconductor field-effect-transistors (MOSFETs) on a heteroepitaxial diamond substrate with an Al2O3 dielectric and a passivation layer were characterized. The full-width at half maximum value of the diamond (004) X-ray rocking curve was 205.9 arcsec. The maximum output current density and transconductance of the MOSFET were 172 mA/mm and 10.4 mS/mm, respectively. The effect of a low-temperature annealing process on electrical properties was also investigated. After the annealing process in N2 atmosphere, the threshold voltage (Vth) and flat-band voltage (VFB) shifts to negative direction due to loss of negative charges. After annealing at 423 K for 3 min, the maximum value of hole field effective mobility (μeff) increases by 27% at Vth − VGS = 2 V. The results, which are not inferior to those based on homoepitaxial diamond, promote the application of heteroepitaxial diamond in the field of electronic devices.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma15072557

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