Peculiarities of admittance spectroscopy study of wide bandgap semiconductors on the example of diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-01-01 |
| Journal | E3S Web of Conferences |
| Authors | Anna Solomnikova, Vadim Lukashkin, Oleg Derevianko |
| Institutions | Peter the Great St. Petersburg Polytechnic University, Saint Petersburg State Electrotechnical University |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study focuses on optimizing admittance spectroscopy (AS) techniques to accurately characterize wide bandgap semiconductors (WBS), specifically boron-doped diamond, where incomplete impurity ionization presents a significant measurement challenge.
- Core Value Proposition: Established a robust methodology for high-precision determination of impurity activation energy (Ea) in WBS by systematically mitigating systematic and random experimental errors.
- Material and Impurity: Single-crystal diamond (HPHT synthesized) doped with boron (p-type acceptor).
- Key Achievement (Ea): Boron activation energy was accurately determined as 293 ± 2 meV, achieving a Mean Squared Error (MSE) of less than 1%.
- Signal/Noise Optimization: The test signal amplitude was increased to 80 meV to overcome the low conductance response caused by the low free carrier concentration (0.2% ionization at room temperature).
- Thermal Hysteresis Elimination: The temperature ramp rate was drastically reduced to approximately 0.5 K/min to ensure thermal equilibrium and eliminate hysteresis in the conductance spectra.
- Thermal Stabilization: A minimum thermostating time of 15 minutes was established as optimal for acquiring accurate frequency conductance spectra (G-f), preventing shifts in the conductance peak frequency.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Boron Activation Energy (Ea) | 293 ± 2 | meV | Calculated from thermal conductance spectra |
| Mean Squared Error (MSE) | < 1 | % | Precision of Ea calculation |
| Optimized Test Signal Amplitude | 80 | meV | Used to maximize signal/noise ratio |
| Optimized Temp. Ramp Rate | ~0.5 | K/min | Used to eliminate thermal hysteresis |
| Minimum Thermostating Time | 15 | minutes | Required for accurate G-f spectra acquisition |
| Schottky Contact Material | Platinum (Pt) | N/A | Upper contact |
| Schottky Contact Diameter | 130 | ”m | Size of circular contacts |
| Contact Thickness | 100 | nm | Pt Schottky and Ohmic contacts |
| Measurement Temperature Range | 20 - 450 | °C | Janis CCR-10-2 probe station capability |
| Measurement Frequency Range | 1 kHz - 2 | MHz | Agilent E4980A RLC-meter capability |
| Diamond Ionization at RT | 0.2 | % | Challenge for electrical characterization |
| Baliga Figure of Merit (BFOM) | 474 | Normalized to Si=1 | High-power switching potential |
| Johnson Figure of Merit (JFOM) | 6009 | Normalized to Si=1 | High-frequency potential |
Key Methodologies
Section titled âKey MethodologiesâThe study utilized Dynamic Admittance Spectroscopy (DAS) to characterize boron-doped diamond, focusing heavily on optimizing the measurement environment to account for the materialâs wide bandgap properties.
- Sample Synthesis and Structure:
- Single-crystal diamond plates were synthesized using the High Pressure High Temperature (HPHT) method.
- A multisectorial structure was used, containing areas of varying boron concentration (low-doped/white and heavily-doped/blue).
- Contact Fabrication:
- Schottky Contact: An array of 130 ”m diameter, 100 nm thick Platinum (Pt) contacts were deposited on the upper side at 300 °C.
- Ohmic Contact: A complete 100 nm thick Pt layer was deposited on the bottom side at 70 °C.
- Experimental Setup:
- Measurements were performed using an Agilent E4980A RLC-meter and a Janis CCR-10-2 closed-cycle helium probe station, controlled by a LakeShore 336 temperature controller.
- The sample was placed on a ceramic cell (rather than a Sitall wafer) inside the probe station to reduce induced noise and minimize the thermal capacity of the substrate.
- Signal/Noise Ratio Adjustment:
- The test signal amplitude was increased from 30 meV to 80 meV. This increase was necessary to obtain a measurable conductance response from the low-doped diamond, compensating for the low concentration of free carriers.
- Temperature Control Optimization:
- The temperature change speed (Ramp Rate) was reduced from an initial 4 K/min to approximately 0.5 K/min to eliminate significant thermal hysteresis in the conductance spectra.
- A thermostating time of 15 minutes was implemented before recording frequency conductance spectra (G-f) to ensure the sample reached the desired setpoint temperature, preventing a 20% error in peak frequency determination.
- Data Extraction:
- The activation energy (Ea) of the boron impurity was calculated from the Arrhenius plot derived from the thermal conductance spectra (G/Ï vs. T).
Commercial Applications
Section titled âCommercial ApplicationsâThe accurate characterization of boron activation energy in diamond is crucial for developing high-performance electronic devices that leverage diamondâs superior material properties compared to traditional semiconductors (Si, SiC, GaN).
| Industry Sector | Application Focus | Relevance of Diamond Properties |
|---|---|---|
| High-Power Electronics | Power converters, high-voltage switches, inverters, and motor drives. | Highest Baliga Figure of Merit (BFOM = 474x Si), enabling low loss and high breakdown voltage. |
| High-Frequency RF/Microwave | 5G/6G base stations, radar systems, high-power amplifiers. | Highest Johnson Figure of Merit (JFOM = 6009x Si), allowing for high-speed, high-power operation. |
| Thermal Management | Heat spreaders, substrates for high-density integrated circuits (ICs) and photonics. | Highest Keyes Figure of Merit (KFOM = 35x Si) due to giant thermal conductivity, crucial for reliability. |
| Semiconductor Manufacturing | Quality control and process optimization for WBS substrates (e.g., SiC, GaN, Diamond). | Accurate impurity characterization (Ea) ensures predictable doping profiles and device yield. |
| Extreme Environment Electronics | Sensors and electronics operating under high temperature or radiation conditions. | Diamondâs large bandgap and robust structure ensure stability where Si or GaAs fail. |
View Original Abstract
To improve the performance characteristics of power and high-frequency electronics, wide bandgap semiconductors are now widely used. This paper presents consideration of features arising during exploration of electronic characteristics of wide bandgap materials. We use the admittance spectroscopy method for analyzing free carrier concentration and boron-impurity activation energy in semiconductor diamond. The special aspect that should be taken into account while studying wide bandgap materials is incomplete ionization of impurity. In this work we adjust the experimental conditions, basing on the previous experience, in particular reduce signal/noise ratio and reckon with heat capacity of the samples and substrate. As a result we obtained high quality conductance spectra and activation energy of boron impurity in low-doped diamond.