Electrically stimulated optical spectroscopy of interface defects in wide-bandgap field-effect transistors
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-01-31 |
| Journal | Communications Engineering |
| Authors | Maximilian W. Feil, H. Reisinger, André Kabakow, Thomas Aichinger, Christian Schleich |
| Institutions | TU Wien, Infineon Technologies (Austria) |
| Citations | 12 |
| Analysis | Full AI Review Included |
Technical Analysis and Documentation: Electrically Stimulated Optical Spectroscopy in Wide-Bandgap FETs
Section titled âTechnical Analysis and Documentation: Electrically Stimulated Optical Spectroscopy in Wide-Bandgap FETsâPrepared for: Engineers and Scientists developing next-generation Wide-Bandgap (WBG) power electronics.
Reference Paper: Feil et al., Electrically stimulated optical spectroscopy of interface defects in wide-bandgap field-effect transistors, Communications Engineering (2023).
Executive Summary
Section titled âExecutive SummaryâThis research presents a critical advancement in characterizing interface defects in wide-bandgap (WBG) power devices, a field highly relevant to 6CCVDâs diamond material offerings.
- Core Achievement: Demonstrated a direct, one-to-one correlation between electrically stimulated photon emission (radiative recombination) and the Threshold Voltage Shift ($\Delta V_{th}$) in a commercial 4H-SiC MOSFET.
- Reliability Link: This correlation optically links the emission spectrum directly to Bias Temperature Instability (BTI) and hysteresis, which are caused by charge trapping in semiconductor-insulator interface defects.
- Novel Methodology: Utilized reverse-side etching and detection to achieve âflawless lightâ access to the SiC/SiO2 interface, minimizing absorption artifacts from intermediate layers (polysilicon gate, SiO2).
- Defect Identification: Spectral analysis of the emitted light (1.4 eV to 3 eV) allowed decomposition into ten distinct optical transitions, enabling the assignment of specific Charge Transition Levels (CTLs) to known interface defects (e.g., C-C, N=N).
- Quantum Access: The method provides a unique opportunity to investigate quantum observables and structural information on defects in fully processed devices, exceeding the capabilities of standard electrical measurements.
- Diamond Relevance: As Diamond is the ultimate wide-bandgap material (5.5 eV) for high-power applications, this non-destructive optical characterization technique is essential for accelerating the development and reliability of Diamond MOSFETs/MISFETs.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the analysis of the 4H-SiC MOSFET device and experimental setup:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Semiconductor Material | 4H-SiC | N/A | Wide-bandgap FET under test |
| SiC Bandgap Energy | 3.26 | eV | Theoretical bandgap energy |
| Diamond/Al2O3 Defect Density (Literature) | 6 x 1012 | cm-2 eV-1 | Cited comparison for WBG interfaces |
| Etched Substrate Thickness | ~185 | ”m | Remaining 4H-SiC thickness for reverse-side detection |
| Gate Voltage Switching Range | -10 to 10 | V | Continuous gate switching stimulus |
| Gate Switching Frequency Range | 50 kHz to 2 | MHz | Range tested for photon flux linearity |
| Detected Emission Spectrum Range | 1.4 to 3 | eV | Broad band emission (visible spectral range) |
| Photo Charge Shift Correlation Slope | 0.086 | pC mV-1 | Linear fit slope relating Qphoto to $\Delta V_{th}$ |
| Pearson Correlation Coefficient | 0.96 | N/A | Strong linear correlation between $\Delta V_{th}$ and photo charge shift |
| SiPM Photodetection Efficiency | ~40 | % | High efficiency for single photon detection |
| SiPM Internal Gain | ~5 x 106 | N/A | Used for high-sensitivity measurements |
| Short-Term Trapping Time Constant ($\tau_{1/e}$) | 130 | ns | Measured during single photo current peak decay |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relied on precise material preparation and advanced optical detection to isolate and analyze radiative recombination events at the SiC/SiO2 interface.
- Reverse-Side Preparation: The commercial 4H-SiC MOSFET was chemically processed (nitric acid, aqua regia) to remove the lead frame and solder. The reverse-side metallization was polished off using diamond paste.
- Substrate Thinning: The remaining 4H-SiC epitaxial layer and substrate were thinned to approximately 185 ”m to ensure transparency for the emitted photons (1.4 eV to 3 eV).
- Electrical Stimulus: A custom microcontroller setup generated ultra-fast gate voltage signals, switching the device between deep accumulation (-10 V) and inversion (10 V) at frequencies up to 2 MHz.
- Optical Detection (Imaging): Emission microscopy visualized the photon flux, confirming localization in the channel region underneath the gate insulator.
- Time-Resolved Detection: A highly sensitive Silicon Photomultiplier (SiPM) was used to detect single photon events, allowing temporal separation of recombination events originating from accumulation-to-inversion and inversion-to-accumulation transitions.
- Spectroscopic Analysis: A fiber-coupled CCD spectrometer recorded the emission spectrum, which was subsequently decomposed using ten Gaussian functions to identify the energetic positions of the Charge Transition Levels (CTLs) of the interface defects.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research highlights the critical need for high-quality, precisely engineered wide-bandgap materials and custom processing to advance power electronics reliability. 6CCVD is uniquely positioned to supply the materials and services required to replicate and extend this research to the next generation of diamond-based devices.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend this research to the ultimate wide-bandgap platform, 6CCVD recommends the following materials:
- Optical Grade Single Crystal Diamond (SCD): Required for high-purity, low-defect substrates necessary for fundamental defect spectroscopy. SCD offers superior transparency across the visible and infrared spectrum, ensuring minimal absorption during reverse-side detection.
- Heavy Boron Doped Diamond (BDD) Films: Ideal for creating highly conductive substrates or back-side contacts in Diamond MISFET structures, facilitating the necessary electrical stimulus and ultra-fast $V_{th}$ readouts used in the methodology.
- Polycrystalline Diamond (PCD) Wafers: Available in large formats (up to 125 mm) for scaling up defect studies or for use as high-thermal-conductivity heat spreaders in power modules.
Customization Potential
Section titled âCustomization PotentialâThe paperâs methodology relies heavily on precise material modification (substrate thinning and metal removal). 6CCVDâs in-house capabilities directly address these requirements:
| Research Requirement | 6CCVD Customization Service | Specification Match |
|---|---|---|
| Substrate Thinning for Optical Access | Custom Thickness Control & Substrates: We provide SCD and PCD wafers with thicknesses ranging from 0.1 ”m to 500 ”m, and substrates up to 10 mm. | We can supply diamond wafers pre-thinned to the required ~185 ”m or less, ensuring optimal optical transparency for reverse-side detection. |
| High-Quality Optical Surface | Precision Polishing: Ultra-low roughness polishing services for both SCD and PCD. | SCD surfaces achieve Ra < 1 nm, critical for minimizing light scattering and maximizing photon collection efficiency. |
| Custom Contact Layers | In-House Metalization: We offer custom deposition of standard and refractory metals. | We can deposit specific metal stacks (e.g., Ti/Pt/Au, W/Cu) or provide wafers with precise metal layer removal/etching services, supporting tailored device fabrication. |
| Large-Area Defect Mapping | Large Format Wafers: Custom dimensions for PCD plates/wafers. | Wafers available up to 125 mm diameter, enabling large-scale emission microscopy studies similar to those performed on the commercial SiC chip. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in the growth and characterization of MPCVD diamond for advanced electronic and quantum applications. We offer consultation services to assist researchers transitioning from SiC/GaN platforms to diamond. Our expertise ensures optimal material selection and processing parameters for similar Electrically Stimulated Optical Spectroscopy projects targeting diamond-insulator interfaces (e.g., Diamond/Al2O3 or Diamond/SiO2).
Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract Wide-bandgap semiconductors such as silicon carbide, gallium nitride, and diamond are inherently suitable for high power electronics for example in renewable energy applications and electric vehicles. Despite the high interest, the theoretical limit regarding device performance has not yet been reached for these materials. This is often due to charge trapping in defects at the semiconductor-insulator interface. Here we report a one-to-one correlation between electrically stimulated photon emission and the threshold voltage shift obtained from a fully processed commercial 4H-SiC metal-oxide-semiconductor field-effect power transistor. Based on this observation, we demonstrate that the emission spectrum contains valuable information on the energetic position of the charge transition levels of the responsible interface defects. We etch back the transistor from the reverse side in order to obtain optical access to the interface and record the emitted light. Our method opens up point defect characterization in fully processed transistors after device passivation and processing. This will lead to better understanding and improved processes and techniques, which will ultimately push the performance of these devices closer to the theoretical limit.