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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]

Thermal management of electronic devices under extreme temperature conditions is very important. Carbon-based materials with low thermal resistance are beneficial for cooling electronic devices, while aerogels with high thermal resistance play a role in thermal insulation. However, achieving both thermal conduction and thermal insulation using the same material is a significant challenge. Herein, a graphene aerogel was synthesized by a solvothermal method, and the thermal resistance of the graphene aerogel was decreased by high-temperature annealing. The elastic graphene aerogel with tunable thermal resistance makes it possible to have dual functions of thermal insulation and thermal conduction. The thermal resistance of the graphene aerogel with 80% compressive strain is 3.3 times lower than that of the original state. During the process of thermal management for lithium-ion batteries (LIBs), the original graphene aerogel acts like a thermal insulator, preventing heat loss from LIBs when the ambient temperature is low (−20 °C), resulting in a temperature improvement of 9 °C and enhancing the discharge capacity of LIBs by 26%. In contrast, when the operating temperature is high (40 °C), the compressed graphene aerogel with low thermal resistance acts as a thermal interface material, dissipating the excessive heat from LIBs and preventing overheating. [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]

In this report, 4H-SiC p-i-n photodiodes with various micro-hole arrays are fabricated, then measured and discussed by using photoelectric measurement system and simulation software. Periodic micro-hole arrays etched from p layer to i layer are obtained by using the selective etching technology, which increases the photosensitive area of devices and reduces the ultraviolet light absorption of p layer. The average dark current of devices has an ultralow value of approximate $6.0\times 10 ^{-15}$ A in the low reverse bias range of 0–10 V. Furthermore, the device with $4 ~\mu \text{m}$ micro-hole exhibits the best performance and its peak responsivity increased by 10.4 % compared to the conventional device. It is significant that the peak responsivity and corresponding external quantum efficiency of devices with $4 ~\mu \text{m}$ micro-hole at 40 V bias are 815 % and 819 % higher than those of devices without micro-hole, respectively. This is attribute to the fact that a high electric field is observed around the micro-holes as the reverse bias increased to 40 V, which leads to local avalanche. Thus, the local avalanche photodiodes work at a relatively low bias, which improved the responsivity and quantum efficiency of the device enormously. [ABSTRACT FROM AUTHOR]

Recently, organic–inorganic hybrid perovskites (OIHPs) are rising as promising candidates for light-emitting applications, due to their superior optical properties. High performance light-emitting applications such as scintillators require minimum non-radiative recombination and high fractions of radiative recombination. Here, we report a simple solution-processing strategy for the synthesis of funnel-type CH3NH3(MA)PbCl3/CH3NH3(MA)PbBrxCl3−x heterostructure perovskite materials that improve the light emission performances. The single crystal X-ray diffraction pattern indicates that the lattice mismatch is only ∼3.24% in the heterointerface. The halide gradient is helpful for driving the photoexcited carriers from the internal high bandgap material to the low bandgap light-emitter layer. The steady-state photoluminescence (PL) and radioluminescence (RL) spectra show that the luminescence intensity has been significantly improved by this heterostructure perovskite. Time-resolved photoluminescence (TRPL) exhibits carrier transport along the halide gradient. Our research suggests that the gradient halide perovskite heterostructure with specific optical properties could be a prospect for commercial scintillator applications. [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]

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]

We report on the fabrication and characterization of very low-dark-current \TiO2 metal–semiconductor–metal ultraviolet (UV) photodetectors (PDs) with Pt Schottky contacts. The dark current of the PDs is merely 1.28 pA at a 5-V bias, which is much better than the previously reported data. The photoconductive gain is less than one for a bias of less than 10 V. The remarkable reduction of the dark current and the gain can be attributed to the combined effect of the large Schottky barrier height produced at the \Pt/TiO2 contacts and the high quality of the sputtered \TiO2 films, such as low intrinsic carrier concentration, large grain size, and absence of oxygen vacancies. The PDs also display a high quantum efficiency and a large UV-to-visible rejection ratio of about three orders of magnitude. [ABSTRACT FROM AUTHOR]

This article investigates the radiation effects on as-deposited and annealed AlN films on 4H-SiC substrates under gamma-rays. The AlN films are prepared using plasma-enhanced-atomic-layer-deposition on an n-type 4H-SiC substrate. The AlN/4H-SiC MIS structure is subjected to gamma-ray irradiation with total doses of 0, 300, and 600 krad(Si). Physical, chemical, and electrical methods were employed to study the variations in surface morphology, charge transport, and interfacial trapping characteristics induced by irradiation. After 300 krad(Si) irradiation, the as-deposited and annealed samples exhibit their highest root mean square values of 0.917 nm and 1.190 nm, respectively, which is attributed to N vacancy defects induced by irradiation. Under irradiation, the flatband voltage ( V fb ) of the as-deposited sample shifts from 2.24 to 0.78 V, while the annealed sample shifts from 1.18 to 2.16 V. X-ray photoelectron spectrum analysis reveals the decomposition of O-related defects in the as-deposited AlN and the formation of Al(NO x ) y compounds in the annealed sample. Furthermore, the space-charge-limits-conduction (SCLC) in the as-deposited sample is enhanced after radiation, while the barrier height of the annealed sample decreases from 1.12 to 0.84 eV, accompanied by the occurrence of the SCLC. The physical mechanism of the degradation of electrical performance in irradiated devices is the introduction of defects like N vacancies and O-related defects like Al(NO x ) y . These findings provide valuable insights for SiC power devices in space applications., (© 2024 IOP Publishing Ltd.)