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We report on high-performance 4H-SiC-based p-i-n ultraviolet (UV) photodiodes and investigation of the capacitance characteristics. The fabricated p-i-n photodiode exhibits a large UV-to-visible rejection ratio ( R 266 nm / R 380 nm ) while displaying a low dark current and a high responsivity at room temperature. Interestingly, even at 450 k, the photodiode presents a high responsivity of 0.15 A/W and high UV-to-visible rejection ratio more than 200. Capacitance-voltage measurements reveal that the 4H-SiC p-i-n photodiode presents strong frequency-, temperature-, and wavelength-dependent capacitance properties. These results indicate that the advances on the 4H-SiC material and the p-i-n junction offer exciting opportunities for important UV detection in a variety of commercial and military fields. [ABSTRACT FROM AUTHOR]

High‐quality epitaxial graphene is prepared on semi‐insulated 4H‐SiC (0001) by ultra‐high vacuum thermal decomposition method and used in graphene/SiC/graphene ultraviolet‐visible dual‐band photodetectors. The dual‐band detector exhibits an extremely low dark current (5.2 × 10−14 A) and a peak responsivity of 1.17 A W−1 corresponding to an external quantum efficiency of 518%. A high detectivity of 3.14 × 1014 Jones is achieved under 280 nm light illumination at 30 V, while a high response speed is obtained with a rise time of 25.17 ns and a decay time of 540.10 ns. The detector shows a responsivity of 1.4 × 10−5 A W−1 and a detectivity of 6.5 × 109 Jones under 430 nm light illumination. The dual‐band detector equipped with SiC grating and asymmetrical graphene electrodes is demonstrated for high‐performance optoelectronic logic "AND" gate with high detectivity at 280 and 430 nm. [ABSTRACT FROM AUTHOR]

A high-performance 4H-SiC p-i-n photodetector for visible-blind ultraviolet (UV) applications has been designed and fabricated. The electrical and optical characteristics were measured at room temperature. The photodetector suffered from significant dark current of 2.5 pA/mm2 at reverse bias of 5 V, and the UV light photocurrent was larger than four orders of magnitude higher than the dark current. The built-in potential and the unintentional i-layer doping concentration were obtained from capacitance-voltage (C-V) measurements. The spectral peak responsivity of the detector reached 0.13 A/W at a wavelength of 270 nm, corresponding to a maximum external quantum efficiency of ∼61%. And the ratio of responsivity at 270 nm to that at 380 nm was >103. The characteristics imply that the photodetector has a great improved ultraviolet-visible rejection ratio which is needed for ultraviolet signal detection. [ABSTRACT FROM AUTHOR]

Thermal oxidation and hydrogen annealing were applied on a 100 μm thick Al-doped p-type 4H-SiC epitaxial wafer to modulate the minority carrier lifetime, which was investigated by microwave photoconductive decay (μ-PCD). The minority carrier lifetime decreased after each thermal oxidation. On the contrary, with the hydrogen annealing time increasing to 3 hours, the minority carrier lifetime increased from 1.1 μs (as-grown) to 3.14 μs and then saturated after the annealing time reached 4 hours. The increase of surface roughness from 0.236 nm to 0.316 nm may also be one of the reasons for limiting the further improvement of the minority carrier lifetimes. Moreover, the whole wafer mappings of minority carrier lifetimes before and after hydrogen annealing were measured and discussed. The average minority carrier lifetime was up to 1.94 μs and non-uniformity of carrier lifetime reached 38% after 4-hour hydrogen annealing. The increasing minority carrier lifetimes could be attributed to the double mechanisms of excess carbon atoms diffusion caused by selective etching of Si atoms and passivation of deep-level defects by hydrogen atoms. [ABSTRACT FROM AUTHOR]

Graphene/SiC/graphene photodetectors were fabricated by epitaxial graphene prepared on semi-insulated 4H-SiC (0001) using the ultra-high vacuum high-temperature thermal decomposition method. The device exhibits a maximum responsivity of 0.01 A/W, a 103 UV–visible rejection ratio, and a high detectivity of 1.34 × 1012 Jones with a ultra-low saturation dark current of 3 × 10−13 A. Interfacial quantum states were adopted at graphene/4H-SiC heterojunction for tuning the Schottky barrier by reverse bias. The extracted Schottky barrier heights decrease from 0.91 to 0.81 eV with bias due to the upward shift of the charge-doped graphene's Fermi level. The peak responsivity of the detector is tuned from 260 to 300 nm, which indicates SiC photogenerated carriers are released from the interfacial quantum states by applied bias. More carriers transit over the Schottky barrier so that the photodetectors achieve high photoelectric conversion. [ABSTRACT FROM AUTHOR]

• A UV photodetector with excellent electrical properties based on Cs 4 PbI 6 single crystals has been fabricated. • The device exhibits good UV detection performances at 1 V bias. • The device exhibits a long-time stability under the temperature from 303 K to 404 K and air. In this work, a high-performance and stable UV photodetector is reported that is based on solution-processed lead bulk Cs 4 PbI 6 single crystals. The Cs 4 PbI 6 single crystals are demonstrated with unique 0D structural and high visible transparent with the wide optical bandgap at 3.46 eV. The crystals exhibit excellent electrical properties with a large μτ value of 9.5 × 10-4 cm2 V-1 and a low trap density of 1.7 × 1010 cm-3. Further, a symmetrical Au-semiconductor-Au structured ultraviolet photodetector based on Cs 4 PbI 6 single crystals has been achieved. The device has been demonstrated with good UV detection performances at 1 V bias: low dark current density of 63.6 nA cm-2, the ratio of the photocurrent to the dark current was about 728 times, fast time profile (response time and recovery time are 11.65 and 12.80 μs, respectively), high UV response (responsivity of 5.07 mA W-1). In addition, the device has good environmental stability under the temperature from 303 K to 404 K and air. This work proves that Cs 4 PbI 6 is a competitive candidate for ultraviolet photon detectors with high detection performance and strong environmental stability. [ABSTRACT FROM AUTHOR]

Abstract: The separate absorption and multiplication (SAM) 4H–SiC ultraviolet (UV) avalanche photodetectors (APDs) have been designed, fabricated and characterized. A gain higher than 1.8×104 was achieved at 90% breakdown voltage of ∼55V. At 0V, the peak absolute responsivity was estimated to be larger than 0.078A/W at 270nm, corresponding to a peak external quantum efficiency of over 35.8%. The long-wavelength cutoff was about 380nm. In addition, the UV-to-visible rejection ratio of around three orders of magnitude was extracted from the spectra response. When the reverse bias was larger than 35V, the spectral responsivity enhanced distinctly. At the reverse bias of 42V, the peak responsivity increased to 0.203A/W at 270nm, corresponding to a maximum external quantum efficiency of ∼93%, which showed a distinct avalanche behavior. Furthermore, the ideality factor around 1.65 and the spectral detectivity about 3.1×1013 cmHz1/2 W−1 were estimated. In conclusion, the 4H–SiC APD have excellent performance for UV detection. [Copyright &y& Elsevier]

With the continuous advancement of electronic devices, there is an urgent need for advanced thermal interface materials (TIMs) to prevent high-power density electronics from overheating. The orderly arrangement of thermally conductive fillers in TIMs plays a crucial role in enhancing thermal conduction along preferred directions. However, it is challenging to control the orientation of the fillers, especially for two-dimensional fillers. In this study, graphene nanoplates (GNPs) were co-planarly arranged in polyvinyl alcohol (PVA) using a rotating magnetic field, which significantly increased the thermal conductivity of the composites. The coplanar vertically aligned GNPs/PVA (CVGNPs/PVA) exhibited a through-plane thermal conductivity of 11.78 W m−1 K−1, which is about 10 times higher than that of the composites with disorderly distributed GNPs (1.14 W m−1 K−1). The rotating magnetic field facilitated the alignment of GNPs and increased face-to-face contact between adjacent GNPs, which significantly boosted the through-plane thermal conductivity of the composite. The compressive modulus of the CVGNPs/PVA composites was only 1.06 MPa, and it helped to reduce the thermal interface resistance to 49 mm2 K W−1. These results offer a novel approach for preparing excellent TIMs that could be used in various applications. GNPs are oriented more compactly and orderly in PVA by using the rotating magnetic field, resulting in a densified thermal conductive paths and higher thermal conductivity of the composite. [Display omitted] [ABSTRACT FROM AUTHOR]

4H‐SiC ultraviolet p‐i‐n photodiodes with four different epitaxial structures were fabricated. The experimental results prove that both a thin P+‐type Ohmic contact layer and a thick intrinsic layer were indispensible for a high‐performance ultraviolet p‐i‐n photodiode. A 4H‐SiC p‐i‐n photodiode with responsivity as high as 0.139 A/W at 278 nm incident wavelength was achieved. Meanwhile, within a certain wavelength range, the peak response wavelength of an ultraviolet p‐i‐n photodiode would be modulated by properly varying the thicknesses of P+‐type layer and the intrinsic layer. Moreover, the theoretical calculation was carried out to further authorise the experimental results. [ABSTRACT FROM AUTHOR]

Abstract: We designed Mg-doped InGaN/GaN quantum well (QW), strained ultrathin InN/GaN QWs, and Mg and Si δ-doped AlGaN/GaN superlattices (SLs) by using first-principles simulations. The designed structures were grown by metal–organic vapor phase epitaxy (MOVPE) on high-quality thick GaN using an interruption technique. The injection-current-dependent electroluminescence characteristics of Mg-doped QW exhibit smaller injection-current-induced blueshift and energy separation, which indicate that modification of quantized levels has occurred in Mg-doped QW due to the reduction of polarization field. The cathodoluminescence intensity of the strained ultrathin InN/GaN QWs is enhanced with increasing barrier thickness due to the suppression of interwell coupling, while the emission wavelength redshifts significantly as the well width increases due to reduction of strain in the QW. Higher hole concentration and mobility are achieved in Mg and Si δ-doped p-type SLs compared to those in modulation-doped SL. These results are in excellent agreement with those of theoretical designs. [Copyright &y& Elsevier]

On the semi-insulating 4H–SiC (0001) surface, hydrogenated multilayers graphene (MLG) were epitaxially prepared by the method of Joule heating decomposition in the hydrogen atmosphere. The structural and chemical characteristics of multilayers graphene have been elaborately analyzed by the X-ray photoelectron and Raman spectroscopies, showing the level of hydrogenation being promoted with the increase of hydrogen pressure. Then, diodes with MLG/4H–SiC contact were fabricated and studied, proving that the Schottky barrier height (SBH) of MLG/4H–SiC junction was enhanced by the hydrogenation. By studying the typical current-voltage characteristics, the SBH was observed to be heightened from 0.84 eV to 1.0 eV along with the hydrogen pressure increasing from 10−2 mbar to 102 mbar. Finally, graphene-semiconductor-graphene photodetectors were fabricated, showing peak responsivity as high as~ 0.9 A/W and external quantum efficiency of 345%, under the 324 nm illumination and biased at 3V. Image 1 • A Joule heating decompostion method has been employed. • Bandgap of epitaxial multilayers graphene could be opened and modulated by different level of hydrogenation. • Schottky barrier height as high as a 1.0 eV have been achieved at the 102 mbar hydrogen pressure. [ABSTRACT FROM AUTHOR]