Key Engineering Materials Vol. 1056

Abstract: This paper presents the development of a confocal Optically Detected Magnetic Resonance (ODMR) system to study diamond and Silicon Carbide (SiC) for reactor dosimetry and quantum defect analysis. Initially, Nitrogen-Vacancy (NV) centers in diamond were characterized to establish a performance baseline, followed by plans to map and quantify color center populations in SiC crystals before and after alpha and neutron irradiation. By correlating ODMR data with electrical performance metrics, we aim to optimize fabrication and annealing protocols to investigate fast neutron sensitivity. The ODMR system, integrated with a home-built confocal microscopy setup, includes a microwave antenna, magnet, laser, objective, and advanced measurement devices such as Si-APD and Time Tagger 20 for high-resolution T2* and T2 measurements. The characterization of the instrument includes high-resolution fluorescence and ODMR spectra of NV centers in diamond, and improved resolution with confocal optics. Ongoing work focuses on correlating luminescence with reactor neutron fluence and the long-term goal is for the advancing SiC irradiation for integrated spin defect analysis.

Abstract: Silicon vacancies (V_Si) are relevant for quantum technologies, including sensing, computing, and communication. For the realization of quantum photonic integrated circuits (QPICs) and, therefore, co-integration of optical and electrical devices with resonant excitation through the wafer surface, a-plane 4H-SiC wafers are required. Transferring established complementary metal-oxide-semiconductor (CMOS)-compatible processes from c-plane to a-plane wafers is, therefore, a crucial step. In this work, key fabrication steps, namely ion implantation, thermal oxidation, and ohmic contact formation, were investigated for a-plane 4H-SiC substrates. To demonstrate successful process transfer, p-channel MOS field-effect transistors were fabricated and electrically characterized, showing comparable I_on/I_off ratios and mobilities to their c-plane counterparts, but with a threshold voltage shift from −7.1 V to −12.0 V on the a-plane. Additionally, tunneling diodes were realized as broadband light emitters, with a significant portion of the emission spectrum falling within the range of off-resonant excitation of V_Si centers. The devices maintained light emission functionality down to cryogenic temperatures.

Abstract: Precise control of optical transitions of color centers like silicon vacancies (V_Si) in 4H-SiC is essential for their functionalization. An applied electric field (E || c) of a pin-diode can be used to tune the optical properties of V_Si centers via the Stark effect, while the associated space charge region under bias suppresses spectral diffusion. Unlike commonly used 4H-SiC c-plane wafers, a-plane wafers allow a scalable fabrication of lateral pin-diodes and resonant laser excitation of the V_Si perpendicular to the wafer surface (a ⊥ c). In this work non-circular lateral pin-diodes oriented perpendicular to the wafer flat were produced in a scalable, CMOS-compatible process. Electrical characterization revealed that 97% of the devices on an a-plane wafer with n-type epitaxial layer were functional, exhibiting breakdown voltages exceeding 200 V and reverse currents below 100 pA/µm, enabling low current noise during optical measurements. The diodes remained operational at cryogenic temperatures after frozen-out charge carriers were re-ionized by the applied electric field. Electron irradiation followed by thermal annealing at 600 °C was used to generate V2 silicon vacancies in the intrinsic region without significantly altering the electrical characteristics. Optically detected magnetic resonance (ODMR) measurements on selected single emitters confirmed the presence of V2 centers by detecting a contrast at 70 MHz, while cryogenic photoluminescence (PL) spectra revealed a zero-phonon line (ZPL) peak at 916 nm.

Abstract: We report a light emitter based on a 4H-SiC lateral Zener diode that is operated under reverse bias in the quantum tunneling regime. Wide bandwidth white light emission with a peak wavelength of 492 nm corresponding to the transition between the nitrogen donor state and the aluminum acceptor state and a full width half maximum breadth of 303 nm at room temperature is shown. The peak breadth can be attributed to the relative shift of the acceptor and donor levels in the high electric field within the space charge region under reverse bias. At the wavelength of 730 nm, which is commonly used for off-resonant excitation of silicon vacancy defects, the emitter achieves 43.1% of its peak intensity. The emitter shows no blue light peak corresponding to the transition between the donor level of nitrogen and the valence band at 391 nm, such as the LED spectrum under forward bias of the same diode does.

Abstract: Point defects in 4H silicon carbide (4H-SiC), such as the silicon vacancy, also known as color centers, offer considerable potential for quantum applications in the fields of quantum sensing as well as computing and communication. The latter two necessitate indistinguishable photons for entanglement swapping and consequently demand precise control over the electronic transition energies, i.e. emission and absorption wavelengths of color centers. One way to achieve this is through monolithic integration of electronic devices in combination with integrated photonics in 4H-SiC. This is considered a potential pathway for scalable quantum photonic integrated circuits. In this paper, we investigate the suitability of a signal-ground-modulator and a vertical pin diode in combination with a waveguide to (i) achieve local field strengths of 5 to 20 MV/m in the crystal’s c-direction, (ii) stabilize the charge state of the silicon vacancy by controlling the local Fermi level, (iii) meet the requirements for photonic single-mode operation, and (iv) minimize the absorption of the evanescent wave due to metal contacts. The findings of the electronic and optical simulations conducted with Synopsys Sentaurus and Ansys Lumerical suggest that the signal-ground-modulator, commonly used in integrated photonics, rarely attains the requisite field strength. In contrast, the vertical pin diode has the potential to meet these requirements even at reduced bias voltages. Furthermore, the intrinsic layer of the diode offers a wide region in which to host the color center in its optically active, negatively charged state.

Abstract: The deployment of silicon carbide (SiC) power devices in aerospace applications is constrained by their unexpected susceptibility to single-event effects (SEEs), despite the inherent advantages of wide bandgap materials. In this work, we experimentally investigate the SEE mechanisms in in-house fabricated 1200 V SiC VDMOSFETs under heavy-ion irradiation using Ta ions with a LET of 75 MeV·cm²/mg. Real-time current monitoring, post-irradiation electrical characterization, and focused ion beam (FIB) analysis were employed to systematically examine device degradation and failure modes under various bias conditions. The results demonstrate a clear progression of damage with increasing bias voltage: no significant changes, single-event gate leakage degradation (SEGLD) at 100 V, single-event leakage current (SELC) in both I_d=I_g and I_d>I_g modes at 300–400 V, and catastrophic single-event burnout (SEB) at 500 V. Structural analyses reveal progressive deepening of gate oxide fractures, extension into the P+ source region, and eventual source metal melting, consistent with the observed electrical degradation. Notably, the threshold voltage remained stable throughout, suggesting that localized damage to limited unit cells has minimal influence on the global device threshold. These findings provide critical insights into SEE-induced degradation pathways in SiC MOSFETs and offer valuable guidelines for the design and radiation hardening of next-generation aerospace power systems.

Abstract: Silicon carbide (SiC) complementary metal-oxide-semiconductor (CMOS) technology and its circuit applications have been rapidly advancing, making the stability and reliability of planar p-channel metal-oxide-semiconductor field-effect transistors (PMOSFETs) increasingly important. In this study, a channel-length-dependent threshold voltage instability was observed under both gate bias stress and gamma-ray irradiation. The results indicate that the majority of positive charge trapping originates from hole injection induced by external bias. Secondary ion mass spectrometry (SIMS) analysis confirmed the retention of aluminum species in the gate dielectric after thermal oxidation. Based on these experimental findings, a dopant diffusion model was proposed, suggesting that dopant contamination in the gate oxide is the primary cause of the channel-length-dependent instability.

Abstract: A laser-based experimental system was developed to investigate Single Event Burnout (SEB) in high-voltage silicon carbide (SiC) devices. By enabling transient measurements under high reverse-bias conditions, the setup emulates ion-induced charge generation with femtosecond laser pulses. Time-resolved waveforms and charge collection trends were obtained, showing consistency with previous heavy ion experiments. This confirms the system’s capability to reproduce SEB-relevant dynamics. Further improvements in spatial resolution and impedance matching are required for detailed analysis of internal charge transport mechanisms.

Abstract: In this paper, the resistance degradation behaviors of double trench (DT) and asymmetric trench (AT) SiC MOSFETs under total ionizing dose (TID) effect and high drain voltage bias are investigated in detail. The output characteristics measurement results before and after irradiation indicate that the TID effect with high drain voltage bias increases the drain current, resulting in the On-state resistance degradation, whereas the high drain voltage bias seems to have no impact on the degradation. In particular, the DT SiC MOSFETs demonstrate a greater degree of degradation in comparison to the AT SiC MOSFETs under the same gate voltage. This phenomenon can be attributed to a more pronounced decline in channel resistance. Simultaneously, the threshold voltage (V_TH), the drain leakage current (I_DSS), and the gate leakage current (I_GSS) are also measured, which can be concluded that the resistance degradation is attributable to the V_TH negative shifting induced by the positive charge accumulation in the gate oxide. Furthermore, the AT SiC MOSFETs have better irradiation tolerance owing to the P-shield asymmetric trench structure, exhibiting slight shift in the V_TH, the I_DSS, and the I_GSS. Finally, the TCAD simulations are utilized to successfully verify the degradation mechanism.