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SiC MOSFETs are increasingly gaining attentions from aerospace industry due to their superior radiation tolerance and low loss. The influences of total ionizing dose (TID) radiation on static characteristics of SiC MOSFETs have been extensively studied in recent years. However, the influence on their switching behaviors has seldom been comprehensively studied yet. In this article, we comparatively studied the switching characteristics of SiC MOSFETs pre and after $\gamma $ -ray radiation. It is observed that their turn-on time and turn-on loss ( ${E}_{\text {ON}}\text {)}$ decrease by 12.78% and 9.19%, and turn-off time and turn-off loss ( ${E}_{\text {OFF}}\text {)}$ increase by 15.92% and 20.79%, respectively, after 500-krad radiation under gate bias ( ${V}_{\text {GS}} =15$ V and ${V}_{\text {DS}} =0$ V), while they are 9.91%, 13.31%, 14.87%, and 28.51% with the same tendency after 500-krad radiation under drain bias ( ${V}_{\text {GS}} =0$ V and ${V}_{\text {DS}} =400$ V). The compensation effect of $\Delta {E}_{\text {ON}}$ and $\Delta {E}_{\text {OFF}}$ is beneficial to power electronic systems from thermal budget point of view. Further investigation indicates that the negative shift of threshold voltage and increment in parasitic capacitances, both of which are induced by accumulation of positive charges in gate oxide, should be responsible for dynamic degradation of SiC MOSFETs after $\gamma $ -ray radiation. Besides, TCAD simulation reveals that the differences in electric field magnitude and distribution under ${V}_{\text {GS}}$ and ${V}_{\text {DS}}$ bias could be the physical mechanism for their different radiation responses. These results provide fundamental knowledge to predict radiation reliability of SiC MOSFETs through switching parameters.

The state-of-the-art field-plate (FP) power MOSFETs are mostly based on a stripe cell pattern. Few attentions were paid to their circular/hexagonal cell patterns. In this article, analytical models are developed to compare the performances between stripe and circular cell patterns for the first time. The proposed models offer a physical insight into the 3-D charge-sharing effect and also a design formula for circular FP power MOSFETs. Numerical results are well consistent with the proposed models. It is revealed through the model that the circular structure with a silicon shell has the best breakdown ability as well as improved trade-off relationship between breakdown voltage (BV) and specific on-resistance. The static performance limit for the circular structure is calculated. Due to the unique 3-D charge-sharing effect, the specific on-resistance for circular structure rated above 100 V can be reduced by more than 50% when compared with the stripe structure.

High hole injection is desired for improving the performance of AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs). In this work, we adopted a compositionally graded p-Aly1Ga1-y1N/Al0.85Ga0.15N superlattice (SL) structure in a nitrogen-polarity DUV LED. Our numerical simulation results show that this SL structure is very beneficial to the hole injection into the active region, and leads to a low turn-on voltage and device resistance. This is significant because a low device resistance means a low power consumption and a high wall-plug efficiency. Meanwhile, a DUV LED with compositionally graded SL has a peak internal quantum efficiency (72%) that is much higher than that of the reference DUV LED without an SL (56%). This work provides an attractive approach to effectively injecting holes into the active region of a nitrogen-polarity AlGaN-based DUV LED.

In this article, the “segmented gate (SG)” concept is proposed and implemented in trench gate to realize both low loss and wide safe-operating area (SOA) for insulated-gate bipolar transistors (IGBTs). The poly gate of the proposed IGBT is split into segments along the trench and each segmented poly gate is surrounded by the poly emitter. This unique 3-D trench architecture is demonstrated under numerical studies to be highly effective in enhancing the short-circuit ruggedness, the turn-off capability, and the latch-up immunity. It enables a 37% reduction in saturation current and a 90% reduction in Miller capacitance. The proposed design also shows an improved trade-off relationship between ON-state voltage and turn-off loss. For the same turn-off loss, the ON-state voltage of the proposed IGBT is reduced by 0.25 V when compared with the conventional carrier-stored trench IGBT.

In this article, we proposed a comprehensive model for predicting the degradation of SiC MOSFETs after gamma-ray irradiation. It is experimentally founded that SiC MOSFETs exhibit different degradation behaviors under gate bias (i.e., ${V}_{\text {GS}} =15$ V and ${V}_{\text {DS}} $ = 0 V) and drain bias (i.e., ${V}_{\text {GS}} $ = 0 V and ${V}_{\text {DS}} =400$ V) in terms of threshold voltage ( ${V}_{\text {TH}}$ ) and ON-resistance ( ${R}_{\text {ds}, \text{ON}}$ ). TCAD simulation shows that gate bias causes a high electric field in gate oxide above the MOS channel region, while drain bias generates relatively lower electric field in gate oxide around near-channel region. The differences in electric field under gate bias and drain bias lead to different hole yields and charge accumulation in gate oxide, which is the underlying physical mechanism for their different degradation behaviors. ${V}_{\text {TH}}$ is chosen as the parameter to quantify the accumulated charges in gate oxide and further predict irradiation-induced degradation. The relationship between the variation of threshold voltage ( ${\Delta} {V}_{\text {TH}}$ ) and the total ionizing doses (TIDs) under both gate and drain bias is formulated and validated. Comparison among measured data, TCAD simulation, and model prediction shows that the maximum prediction error is lower than 0.08 V, which proves the rationale and accuracy of the proposed degradation model. In addition, the two submodels for gate bias and drain bias are unified as one according to the time dependence effect (TDE) for TID irradiation. The proposed model could be useful to predict the degradation and/or lifetime of SiC MOSFETs in irradiation environments.

The fast turn-on speed of silicon carbide (SiC) gate-turn-off (GTO) thyristor is preferred for pulse power applications. However, the turn-on delay phenomenon hinders its improvement. In this article, the dynamic turn-on transient process of SiC GTO thyristor is investigated and analyzed extensively by means of both numerical simulation and physical modeling. The physical mechanism behind its turn-on transient process is discussed in detail. A physical model based on the charge-control theory is proposed to identify the dominant factors influencing the dynamic turn-on transient. Then the theoretical analysis is quantitatively made on the parameter design of GTO’s unit cell, and methods to increase the turn-on switch speed are extensively discussed. This study provides not only in-depth physical insights into the device’s turn-on characteristics, but also designs guidelines for the advancement of SiC GTO thyristor.

Highly efficient hole injection into a AlGaN quantum well is desirable in nitride deep-ultraviolet light-emitting diodes (DUV LEDs) for high optical performance. In this work, we report the observation of enhanced hole injection in the N-polar AlGaN-based DUV LEDs with compositionally graded p-AlxGa_1−xN (x?=?0.65–0.75) by simulation and show that the enhanced hole injection leads to the increase of the peak internal quantum efficiency (IQE) and the significant reduction of efficiency droop at high current density. This work might activate researchers to realize the efficient polarization p-type doping of N-polar AlGaN with high Al content and thus to achieve high performance DUV LEDs experimentally.

Realization of nitrogen-polar (N-polar) AlN on SiC is important for the development of high-performance GaN high-electron mobility transistors (HEMTs). However, AlN films grown on SiC substrates are mostly metal-polar, and it is difficult to achieve an N-polar AlN on them. In this work, we manipulated the lattice polarity of AlN grown on SiC by varying the V/III ratio. Our results show that AlN films grown at a low V/III ratio undergo lattice polarity reversal from N-polarity to metal-polarity near the AlN/SiC interface. This occurs because oxygen enrichment occurs in AlN, forming a thin AlON layer close to the interface. Importantly, we suppress the oxygen enrichment and thus the formation of AlON in AlN under a high V/III ratio, i.e., an N-rich growth condition, and finally achieve an N-polar AlN film on SiC. We also find that the threshold V/III ratio that realizes N-polar AlN on SiC without lattice polarity reversal is ∼6000. Furthermore, we prepared a GaN/AlGaN HEMT structure based on the obtained N-polar AlN, and the 2-dimensional electron gas density and mobility at the heterostructure interface are 1.5 × 1013cm–2and 923 cm2/V·s, respectively. This work is expected to promote the development of N-polar GaN HEMTs on SiC.

Nitrogen-polar (N-polar) wurtzite (WZ)-phase InGaN films suffer from severe zincblende (ZB)-phase inclusions and thus present a rough surface, which severely restricts its application in GaN-based optoelectronic devices. In this paper, several different pulsed modes were adopted to grow N-polar InGaN films with the purpose of suppressing the ZB-phase inclusions, and their effects on the surface morphology and crystal quality of the InGaN films were studied in detail. Our results demonstrate that the pulsed mode of continuously feeding In source while alternately injecting N and Ga sources can effectively suppress the formation of ZB-phase inclusions, due to the increased mobility of group-III adatoms on the N-polar surface. Benefiting from the suppression of the ZB-phase inclusions, the surface roughness of InGaN films is significantly reduced. Meanwhile, the screw dislocation density of the InGaN decreases from 1.4 ​× ​109to 6.0 ​× ​108 ​cm−2. This work provides an approach to the growth of high-quality N-polar InGaN films free of ZB-phase inclusions for N-polar InGaN-based devices.

Surface-enhanced Raman scattering (SERS) is a supersensitive technique for monitoring catalytic reactions. However, building a SERS-kinetics model to investigate catalytic efficiency on the surface or interface of the catalyst remains a great challenge. In the present study, we successfully obtained an excellent semiconducting SERS substrate, reduced MnCo2O4(R-MnCo2O4) nanotubes, whose favorable SERS sensitivity is mainly related to the promoted interfacial charge transfer caused by the introduction of oxygen vacancies as well as the electromagnetic enhancement effect. Furthermore, the R-MnCo2O4nanotubes showed a favorable oxidase-like activity toward oxidation with the aid of molecular oxygen. It was also showed the oxidase-like catalytic process could be monitored using the SERS technique. A new SERS-kinetics model to monitor the catalytic efficiency of the oxidase-like reaction was developed, and the results demonstrate that the Vmvalues measured by the SERS-kinetics method are close to that obtained by the UV–vis approach, while the Kmvalues measured by the SERS-kinetics method are much lower, demonstrating the better affinity between the enzyme and the substrate from SERS results and further confirming the high sensitivity of the SERS-kinetics approach and the actual enzyme-like reaction on the surface of nanozymes, which provides guidance in understanding the kinetics process and catalytic mechanism of natural enzymatic and other artificial enzymatic reactions. This work demonstrated the improved SERS sensitivity of defective semiconductors for the application of enzyme mimicking, providing a new frontier to construct highly sensitive biosensors.

Effective ultraviolet light-emitting diodes (LEDs) were fabricated by clamping the n-ZnO films on the top of p-hBN/p-GaN/sapphire substrates. An ultraviolet emission originating from ZnO was measured from the diode under a forward bias, the electroluminescence (EL) spectra of which show a peak wavelength of ∼376 nm with a narrow full-width at half maximum of ∼12 nm. Compared with the reference diode fabricated by directly growing n-ZnO on the p-hBN substrates using metal–organic chemical vapor deposition, the proposed diode showed a dramatic increment of the EL intensity; meanwhile, its emission onset lowered down considerably. The improved optical property of the proposed LED is mainly ascribed to suppressing the formation of the BNO-related layer at the n-ZnO/p-hBN interface. The present work provides a simple and feasible approach for developing advanced ZnO-based optoelectronic devices.

In this paper, we have demonstrated that Ga-free AlInN can be obtained in the close-coupled showerhead (CCS) reactor metalorganic chemical vapor deposition (MOCVD) system when thorough cleaning was applied. For the AlInN films grown in the CCS reactor routinely used, the serious unintentional incorporation of gallium (Ga) atoms in AlInN was confirmed by the measurement results of secondary ion mass spectroscopy. To avoid the Ga incorporation, we removed the Ga-contained coatings on the surface of quartz liner, wafer susceptor, and showerhead. Then, in the reactor without Ga-contained coatings, Ga-free AlInN films were obtained. Moreover, the effect of growth parameters on the indium incorporation in AlInN and the structural properties of AlInN were studied systematically. It is worth noting that the realization of Ga-free AlInN in the CCS reactor is significantly important because CCS MOCVD system is widely used for the research and mass production of nitride materials and devices.