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The results of electrical characteristics and alpha-particle energy spectrometry of 4H-SiC p-i-n diodes are reported. From the capacitance-voltage measurement, the effective doping concentration of the $80 ~\mu \text{m}$ lightly doped 4H-SiC epitaxial layer used in this work is calculated to be about $2\times 10\,\,^{{13}}$ cm $^{-{3}}$ , approaching the limit of the lowest doping level by the SiC epitaxial growth technique. The detector exhibits consistently low leakage current of picoampere level at a reverse bias of 100 V and superior thermal stability up to 150 °C. Resultantly, an energy resolution of 0.6% has been achieved within a 5486 keV $\alpha $ -particle spectrum, which is comparable to the high-resolution SiC Schottky barrier $\alpha $ -particle detector. Also, near 100% charge collection efficiency has been realized with reverse bias exceeding 25 V. This study thus provides a promising solution to high-performance 4H-SiC radiation detectors with low-voltage operation. [ABSTRACT FROM AUTHOR]

In this work, a prototype solar-blind single-photon imaging lidar based on SiC ultraviolet (UV) avalanche photodiodes (APD) is demonstrated. The SiC APD with a peak responsivity at ~280 nm can greatly lessen the strict solar-blind filtering requirement for the system. When characterized by using a gated quenching circuit, the SiC APD operating in Geiger mode could exhibit a room temperature single photon detection efficiency of ~27% with a dark count probability of $1.59\times 10 ^{-2}$. Based on the SiC APD, a 266 nm nanosecond pulsed laser, a galvanometer scanner and a time-correlated single-photon counter, 3-dimensional depth image with $128\times 128$ resolution is realized by the prototype system in daylight. The average ranging accuracy of the system is found within 28 mm based on current setup. [ABSTRACT FROM AUTHOR]

Extreme ultraviolet (EUV) detectors are key components required in many critical applications. In this work, a high-performance 4H-SiC $\delta \text{n}$ -i-p EUV detector with gradient doping-induced surface junction is designed and fabricated. The detector demonstrates ultra-low leakage current and excellent photo-response uniformity across the ~6 mm2 photo-sensitive area. Under photovoltaic operation mode, the detector exhibits high responsivity of 0.104 A/W and corresponding quantum efficiency of 960%@13.5 nm, which are close to the theoretical limit. Meanwhile, the equivalent noise power of the device under 0 V bias is determined to be $2.35\times {10}^{\text {-12}}$ W by 1/f noise test, proving that the device has a very low noise level and corresponding high detectivity. In addition, the high-temperature working capability and radiation-resistant performance of the EUV detector are preliminarily verified. [ABSTRACT FROM AUTHOR]

Identifying defects/traps is of vital importance for the implementation of high-performance Ga2O3 power devices. In this work, majority and minority carrier traps in beta-gallium oxide ($\beta $ -Ga2O3) have been investigated and identified by means of deep level transient spectroscopy (DLTS) in Ni/ $\beta $ -Ga2O3 Schottky barrier diode (SBD) and NiO/ $\beta $ -Ga2O3 p+-n heterojunction diode (HJD). For both diodes, a dominant energy level of majority carrier (electron) trap states is determined to be ${E}_{C}-$ (0.75–0.79) eV with a concentration of (2.4–4.1) $\times 10^{{13}}$ cm $^{-{3}}$. Meanwhile, an additional trapping level at ${E}_{V} +0.14$ eV with a concentration of 1.2 $\times 10^{{14}}$ cm $^{-{3}}$ yield is present in NiO/ $\beta $ -Ga2O3 bipolar HJD but absent in the Ni/ $\beta $ -Ga2O3 SBD unipolar counterpart. The detection of such minority carrier traps originates from the hole injection through trap-assisted tunneling (TAT) from $\text{p}^{+}$ -NiO to $\beta $ -Ga2O3. The bias- and frequency-dependent DLTS characteristics identify that such shallow-level minority carrier traps are located in the $\beta $ -Ga2O3 bulk region rather not interfacial states at the NiO/ $\beta $ -Ga2O3 heterointerface. The identification of both majority and minority carrier traps in this work may shed light on the in-depth understanding of carrier transport mechanisms in Ga2O3-based unipolar and bipolar power devices. [ABSTRACT FROM AUTHOR]

With a reverse p-n junction in the gate stack design, this work demonstrates a 1.2 kV/25 A normally off p-n junction/AlGaN/GaN high-electron mobility transistor (PNJ-HEMT). Benefiting from the robust gate terminal, the PNJ-HEMT exhibits a large gate breakdown voltage of 18.2 V and a positive threshold voltage of 1.7 V, enabling a wide gate-bias window. Thereafter, with an applicable VGS of 10 V, the transient switching characteristics in nanosecond timescale (11.7-ns rise time and 10.5-ns fall time) and notable immunity to dynamic Ron degradation, as well as record-high dynamic breakdown voltage (1.62 kV) under transient overvoltage have been demonstrated. In particular, rugged reliability is validated after over 1-million times dynamic breakdown with a 1.5-kV peak overvoltage. To the best of our knowledge, this is the first demonstration of high-VGS (10 V) GaN HEMT's circuit-level operating capability with considerable reliability, and has well exceeded the VGS limit of 5–7 V in conventional p-GaN gate-terminal devices, thus possessing great potentials in high-power, high-frequency, and high-reliability applications. [ABSTRACT FROM AUTHOR]

Robustness of GaN power diodes must consider the device ruggedness against out of safe-operating-area events, especially the transient spikes in voltage and current. In this work, intriguing resistive energy dissipating capability against transients was realized in the AlGaN/ GaN Schottky barrier diodes (SBDs), delivering a kilowatt-level sustaining power, which alternatively overcomes the technological bottleneck of non-avalanche behavior in AlGaN/GaN SBDs. In particular, the GaN SBDs achieved a high dissipating energy of 1.5 mJ and a low transient voltage of 445 V, thanks to the partially metallized anode design. Together with rugged repetitive sustaining capability and high-temperature stability, the GaN SBDs with this advanced technical design present enormous potential in high-power, and high-reliability applications. [ABSTRACT FROM AUTHOR]

In this letter, we achieved significantly enhanced avalanche ruggedness and surge current capability in GaN junction barrier Schottky (JBS) diode for highly reliable power operation. Based on the selective Mg-ion implantation technology, the GaN JBS diode obtains superior electrostatic performances, including 830-V breakdown voltage, 150-mΩ specific on-state resistance, and 0.5-V turning on voltage. Meanwhile, zero reverse recovery behaviors are observed even under extreme switching conditions of 600 V/10 A. During the reliability evaluation in the inductive load circuits, crucial avalanche capability with avalanche breakdown voltage over 965 V, avalanche energy up to 57.8 mJ, and more than 10 000 repetitive avalanche breakdown events are demonstrated. Together with the surge current tolerance up to 65 A and surge energy of 6.0 J, a large safe-operation-area under both forward and reverse inductive spikes is realized for the GaN-based rectifier. [ABSTRACT FROM AUTHOR]

In this letter, we report a quasi-vertical GaN junction barrier Schottky diode on low-cost sapphire substrate. With the high quality GaN epitaxy and selective-area p-islands formed via Magnesium ion implantation at the anode region, reverse leakage in level of 10−7 A/cm2 was achieved, as well as a high on/off current ratio of 1010 and a high breakdown voltage of 838 V. Meanwhile, advantageous characteristics as expected in vertical GaN Schottky barrier diode were realized, including a low turn-on voltage of 0.5 V and fast switching performance under 400 V/10 A operation condition. Along with the improved heat dissipation via substrate thinning and packaging techniques, the diode retains a relatively low thermal resistance, enabling high current rectification level over 60 A, power efficiency up to 98.7 %, while maintaining low case temperatures. [ABSTRACT FROM AUTHOR]

Engineering oxide interfaces with defined electronic band structures is of vital importance for designing all-oxide devices with controllable multifunctionality and improved performance. Here, we report the band alignment, band bending, and transport mechanism in the NiO/β-Ga2O3 p-n heterojunction (HJ) which exhibits high performances with a rectification ratio over 1011, a turn-on voltage of 1.87 V and specific ON-resistance of 10.2 mΩ ⋅ cm2. A type-II band alignment is identified at NiO/ β-Ga2O3 HJs with a valence band offset of 3.60 eV and a conduction band offset of 2.68 eV, respectively, determined from the depth-profiled X-ray photoelectron spectroscopic analysis. Besides band edge discontinuity, an additional built-in potential of 0.78 V is observed at the interface due to the charge transfer across the p-n-junction. In comparison, the NiO/β-Ga2O3 p-n HJ has lower leakage current and higher breakdown voltage than that of the Ni/Ga2O3 Schottky barrier diode. Capacitance–frequency analysis indicates the presence of interfacial states, and interface recombination is the dominant transport mechanism. The type-II NiO/Ga2O3 HJ provides favorable energetics for facile separation and transportation of photogenerated electrons and holes, which is important for all-oxide devices that require bipolar operation and power devices with higher conversion efficiencies. [ABSTRACT FROM AUTHOR]

We reported on a fast-speed and self-powered $\beta $ -Ga2O3 vertical Schottky solar-blind photodiodes of 7 mm $\times7$ mm detecting area. Operated at zero bias, this photovoltaic diode exhibits a peak responsivity of 9.78 A/W at 212 nm with its corresponding specific detectivity of $3.29\times 10^{{14}}$ Jones. An UVC-to-UVA rejection ratio over $10^{{4}}$ is also achieved that is mainly limited by the internal photoemission of hot electrons from metal injecting into Ga2O3. In particular, the diode exhibits a recorded shortest response time of $ < 5~\mu \text{s}$ , which is the first report of RC-time-limited performance for Ga2O3 photodetectors reported to date. Along with the large sensitive area, high detectivity and fast response speed allows them suitable for the real time response to objectives with high speed and weak flux of solar-blind spectral signal or high-energy radiations. [ABSTRACT FROM AUTHOR]

In this work, the after-pulse properties of 4H-SiC ultraviolet (UV) avalanche photodiodes (APDs) working in gated quenching mode are firstly characterized by using a double gate method. The after-pulse probability is determined as a function of delay time at various overbias voltages and temperatures. It is found that the after-pulse probability of 4H-SiC APDs would decrease at higher chip temperature, supporting the carrier trapping/releasing mechanism. Compared to state-of-the-art Geiger-mode Si APDs, the 4H-SiC APD exhibits considerably larger after-pulsing effect, which should be mainly caused by high density point defects within the SiC epilayer. The maximum signal repetition rate of the SiC APD in gated quenching operation mode is estimated, which is a key performance parameter for future UV laser radar and quantum communication applications. [ABSTRACT FROM AUTHOR]

In this work, the effect of very high-fluence 100 MeV proton radiation on the performance of 6H-SiC photoconductive proton detectors is studied. The irradiation fluence is up to ${1.6}\times {10}^{{{17}}}{\mathrm {cm}}^{{\text {-2}}}$ and the degradation process of the SiC detector is continuously monitored for the first time. Before proton irradiation, the detector shows a low dark current of ~0.8nA/cm2 at 1000 V bias. As the irradiation fluence increases, the dark current continuously drops, which should be caused by irradiation damage induced carrier compensation defects. Meanwhile, the output current of the SiC detector shows an exponential decay behavior and tends to saturate at irradiation fluence up to ${5}\times {10}^{{{16}}}{\mathrm {cm}}^{{\text {-2}}}$. At the end of the very high fluence irradiation test, the detector still exhibits ~20% of its original output current value, suggesting the excellent radiation hardness of SiC for proton detection. [ABSTRACT FROM AUTHOR]

In this paper, carrier transport and gain mechanisms are exploited in the $\beta $ -Ga2O3-based metal–semiconductor–metal photodetectors with Au back-to-back Schottky contacts. The resultant devices exhibit a low dark current of <10 pA at 10 V, a sustaining bias over 500 V without electric breakdown, a self-powered sensitivity with a UVC-to-visible rejection ratio over $10^{{3}}$ , and a photo-to-dark current ratio of 50 at 473 K, indicative of its strong operation capability at high temperature and in harsh environments. Temperature-dependent current–voltage features reveal that the dark reverse leakage is dominated by the thermionic field emission at low electric field and Poole–Frenkel emission from a deep trap level of 0.42 eV under the conduction band at high field, respectively. These negatively charged traps positioned below the Fermi level in the vicinity of Schottky interface capture photogenerated holes and reduce the barrier height upon illumination. The temperature- and bias-dependent photoresponse features are identified in physics that the photoconductive gain as well as slow response speed is originated from the change of barrier height due to trap repopulation. [ABSTRACT FROM AUTHOR]

4H-SiC avalanche photodiodes (APDs) working in Geiger mode are promising devices for ultra-weak ultraviolet light detection. In this letter, the degree of avalanche uniformity across device mesa of 4H-SiC p-i-n APDs is studied by imaging hot carrier luminescence pattern of the devices in avalanche regime. It is found that the luminescence emission from the APD under avalanche always first appears in the [ $\overline 1 \overline 1 20$ ] side of the top contact electrode. As over-bias increases, the luminescence pattern gradually extends toward the [ $11\overline 2 0$ ] direction and finally covers the whole device mesa. A physical model is proposed to explain the non-uniform avalanche phenomenon, in which the substrate off-orientation related carrier lateral drift would cause asymmetric hole accumulation and screening of junction electrical field along the [ $11\overline 2 0$ ] direction. [ABSTRACT FROM AUTHOR]

In this letter, in order to improve avalanche characteristics in deep ultraviolet range and enhance fill factor, vertical 4H-SiC n-i-p-n avalanche photodiodes (APDs) are designed and fabricated, in which avalanche current flows through a forwardbiased p-n junction formed between the p epi-layer and the n-type substrate. Compared with a traditional n-i-p APD, no obvious difference of gain-voltage and photo-response characteristics is observed, indicating the feasibility of the proposed n-i-p-n device structure. When a partial trench isolation scheme is applied, the vertical n-i-p-n APD shows a high fill factor of 78.3% and a low-bias quantum efficiency of 66%. [ABSTRACT FROM AUTHOR]

In this paper, 4H-SiC separated absorption charge and multiplication ultraviolet avalanche photodiodes (APDs) with small gain-voltage slope and enhanced fill factor are designed and fabricated. As a special reach-through structure, the absorption layer of the APD is fully depleted at breakdown voltage, which can share a considerable portion of reverse bias. As a result, the sensitivity of electric field within the multiplication layer as a function of overbias is reduced, leading to a small gain slope. Given the fact that the impact ionization coefficient of holes is less sensitive to electric field variation than that of electrons, the APD is also designed to be a hole-initiated ionization type, which can further reduce the gain slope. Meanwhile, three different top-electrode geometric patterns of SiC APDs are designed, and their impact on APD performance is investigated for the first time. Severe current crowding effect is observed in the forward current–voltage (I–V) characteristics of the APD with a traditional dot top-electrode, indicating inefficient current spreading across the top contact layer due to nonnegligible lateral resistance. In contrast, the forward I–V characteristics and photo-current at the avalanche regime of the APDs with optimized branch-shaped top-electrodes are apparently improved, owing to the improvement of electric field distribution and avalanche multiplication uniformity across the device active area. Furthermore, photon count rate increases by two to four times with larger voltage pulse height, suggesting enhanced effective avalanche multiplication area and fill factor. [ABSTRACT FROM PUBLISHER]

In this letter, a high-performance 4H-SiC p-i-n ultraviolet (UV) photodiode (PD) with its p layer formed by Al implantation is designed and fabricated. The dark current density of the PD remains lower than 1 nA/cm2 at −100 V in the entire temperature range from room temperature (RT) up to 175 °C. The RT maximum external quantum efficiency of the PD under 0 V bias is 44.4% at 270 nm with a UV/visible rejection ratio larger than 10^4 . The photoresponse characteristics of the PD are studied as the functions of reverse bias and temperature, which suggest that the device is advantageous to detect UV signals in high-temperature harsh environment. Compared with a 4H-SiC p-i-n PD formed entirely by epitaxial growth, the PD formed by Al implantation exhibits larger frequency dispersion in capacitance–voltage measurement, which should be caused by residual structural defects introduced during the ion implantation process. [ABSTRACT FROM PUBLISHER]

In this letter, we report the first demonstration of a 4H-SiC p-i-n ultraviolet (UV) avalanche photodiode (APD) with its p-layer formed by Al implantation. In order to alleviate the electric field crowding around mesa edge, an appropriately doped p sub-layer with high lateral resistance is added beneath the top p+ contact layer, which are both formed by Al implantation into a lightly doped n-SiC layer. The room temperature (RT) dark current of the APD remains lower than 0.1 pA when reverse bias is <200 V, and then increases by several orders of magnitude before avalanche breakdown occurs at \sim 260 V. A maximum avalanche gain larger than 10^{3} can be achieved, while the related breakdown voltage exhibits a positive temperature coefficient of \sim 25$ mV/°C. The activation energy of dark current as well as the relationship between the dark current and the device active area is studied, which suggests that bulk leakage assisted by residual implantation-induced deep-level defects is the dominant source of dark current at high bias. The RT maximum quantum efficiency of the APD under 0 V bias is 44.4% at 270 nm with a UV/visible rejection ratio larger than 10^{4} . [ABSTRACT FROM PUBLISHER]

In this letter, a beveled mesa 4H-SiC ultraviolet (UV) avalanche photodiode (APD) with partial trench isolation is reported. By adopting this partial trench isolation structure, when device diameter of the APD is 150~\mu \textm , its fill factor can increase from 33.9% to 63.5% compared with the traditional full trench isolation structure. The photocurrent of the APD shows corresponding improvement when illuminated with the same UV light source. Through current–voltage, spectral response, and single photon detection characterizations, it is proved that the performance of the partial trench isolation APD does not degrade compared with the traditional full trench isolation structure. The APD fabricated in this letter with partial trench isolation shows a unity-gain peak quantum efficiency of 66.4% at 270 nm and a single photon detection efficiency of 9.5% at 280 nm when the dark count rate is fixed at 1 Hz/ \mu \textm^2 . [ABSTRACT FROM PUBLISHER]

In this letter, a hig-performance inverter based on amorphous indium–gallium–zinc oxide thin-film transistors (TFTs) is fabricated, which consists of an enhancement mode driver and a depletion mode load. By applying an area-selective laser annealing technique, the threshold voltage ( \(V_{\mathrm {th}}\) ) of the load TFT could be tuned from positive to negative gate voltage. Based on X-ray photoelectron spectroscopy analyses, the negative \(V_{\mathrm {th}}\) shift can be attributed to the increase of oxygen vacancy concentration within the device channel upon laser annealing. Meanwhile, compared with conventional inverters with an enhancement mode load, the proposed inverter shows much improved switching characteristics, including output swing range close to 100% full swing as well as an enhanced output voltage gain from −1.5 to −20.5 V/V. [ABSTRACT FROM AUTHOR]

In this letter, GaN-based p-i-n ultraviolet (UV) photodetectors (PDs) are fabricated on patterned sapphire substrate (PSS) for the first time. Based on cathodoluminescence mapping and x-ray diffraction measurement, the as-grown structure on PSS has considerably lower defect density than that of a similar structure grown on standard sapphire substrate (SSS). The PD on PSS exhibits a low dark current density of \sim5.1~nA/cm^2 under -5~V, a high UV/visible rejection ratio of more than 10^4, and a zero-bias peak responsivity of \sim0.19~A/W at 360 nm, which corresponds to a maximum quantum efficiency of 65%. In the photo-sensitive wavelength region between 250 and 365 nm, the quantum efficiency of the PD on PSS is, on average, over 30% higher than that of the control device fabricated on SSS. [ABSTRACT FROM PUBLISHER]