Depletion Region Width Research Articles

2D semimetal with ultrahigh work function for sub-0.1 V threshold voltage operation of metal-semiconductor field-effect transistors

Metal-semiconductor field-effect transistors (MESFETs) offer the advantages of efficient gate control and low power consumption due to the large junction capacitance. However, the strong Fermi-level pinning caused by the metal-induced gap states makes it a great challenge to build a high-quality Schottky junction with a large energy barrier and low leakage current. Moreover, the upper limit of the work function of conventional metals is around 5 eV, which prevents the formation of a wide depletion region and the reduction of power consumption. In this work, 2D semimetals with high work function have been used as the gate to fabricate 2D van der Waals MESFETs. Compared with PtSe2 and PdSe2, TiS2 with ultrahigh work function of 6.6 eV forms the largest Schottky barrier height with MoS2. And TiS2/MoS2 MESFETs display a sub-0.1 V threshold voltage owing to the large built-in potential and exhibit a small subthreshold swing of 73 mV/dec. The tuning of the channel carrier density from the back gate can further optimize the device performance and provide a strategy to build AND logic gate in a dual-gated transistor. Our work successfully demonstrates the use of high-work-function 2D semimetal to realize high-performance MESFET with low power consumption.

Unveiling the dimensional effects of SnO2 quantum dots and nanoparticles on the interfacial properties of perovskite solar cells

SnO2 is the most efficient and widely used electron conductor for perovskite solar cells (PSCs) due to its superior conductivity and high stability, however, the effect of SnO2's dimensions and sizes on the interfacial properties and device stability has often been ignored. Here, we investigate the relationship between device performance and electron conductors, including SnO2 quantum dots (SnO2 QD) and SnO2 nanoparticles (SnO2 NC). In contrast to SnO2 NC, SnO2 QD yields larger perovskite grains and high film uniformity, resulting in remarkable device efficiency and stability. Nonetheless, the device containing SnO2 QD exhibits a significant current-voltage hysteresis. By incorporating SnO2 QD and SnO2 NC to construct a bilayer structure, the hysteresis response and efficiencies of the devices have been drastically altered. PSCs based on SnO2 QDs exhibit a significant capacitive response at low frequencies and an exponential increase in capacitance at lower voltages, indicating significant charge accumulation at the interfaces. After being passivated with SnO2 NC in a bilayer structure, the wide depletion region at the high built-in potential provides a greater driving force for charge transfer, resulting in a significant reduction of hysteresis and an efficiency increase to >21%. This research provides insights into the significance of structural effects on electron conductors and will aid in enhancing the device performance of PSCs.

Infrared Photodetection from 2D/3D van der Waals Heterostructures.

An infrared photodetector is a critical component that detects, identifies, and tracks complex targets in a detection system. Infrared photodetectors based on 3D bulk materials are widely applied in national defense, military, communications, and astronomy fields. The complex application environment requires higher performance and multi-dimensional capability. The emergence of 2D materials has brought new possibilities to develop next-generation infrared detectors. However, the inherent thickness limitations and the immature preparation of 2D materials still lead to low quantum efficiency and slow response speeds. This review summarizes 2D/3D hybrid van der Waals heterojunctions for infrared photodetection. First, the physical properties of 2D and 3D materials related to detection capability, including thickness, band gap, absorption band, quantum efficiency, and carrier mobility, are summarized. Then, the primary research progress of 2D/3D infrared detectors is reviewed from performance improvement (broadband, high-responsivity, fast response) and new functional devices (two-color detectors, polarization detectors). Importantly, combining low-doped 3D and flexible 2D materials can effectively improve the responsivity and detection speed due to a significant depletion region width. Furthermore, combining the anisotropic 2D lattice structure and high absorbance of 3D materials provides a new strategy in high-performance polarization detectors. This paper offers prospects for developing 2D/3D high-performance infrared detection technology.

Toward High Efficient Cu2 ZnSn(Sx ,Se1- x )4 Solar Cells: Break the Limitations of VOC and FF.

Increasingthefill factor (FF) and the open-circuit voltage (VOC ) simultaneously together with non-decreased short-circuit current density (JSC ) are a challenge for highly efficient Cu2 ZnSn(S,Se)4 (CZTSSe) solar cells. Aimed at such target in CZTSSe solar cells, a synergistic strategy to tailor the recombination in the bulk and at the heterojunction interface has been developed, consisting of atomic-layer deposited aluminum oxide (ALD-Al2 O3 ) and (NH4 )2 S treatment. With this strategy, deep-level CuZn defects are converted into shallower VCu defects and improved crystallinity, while the surface of the absorber is optimized by removing Zn- and Sn-related impurities and incorporating S. Consequently, the defects responsible for recombination in the bulk and at the heterojunction interface are effectively passivated, thereby prolonging the minority carrier lifetime and increasing the depletion region width, which promote carrier collection and reduce charge loss. As a consequence, the VOC deficit decreases from 0.607 to 0.547V, and the average FF increases from 64.2% to 69.7%, especially, JSC does not decrease. Thus, the CZTSSe solar cell with the remarkable efficiency of 13.0% is fabricated. This study highlights the increased FF together with VOC simultaneously to promote the efficiency of CZTSSe solar cells, which could also be applied to other photoelectronic devices.

ZnO nanowire network/4H-SiC heterojunction for improved performance ultraviolet photodetector: The effect of different SiC doping concentrations on photoresponse properties

Zinc Oxide (ZnO) and Silicon Carbide (SiC) are highly promising semiconductors with their heterostructures offering pathways for the next generation of sensing and detecting optoelectronics technologies due to their wide bandgaps. Optoelectric properties of ZnO nanowire network and n-type single crystal 4H-SiC heterojunction ultraviolet (UV) photodetectors have been investigated and compared for two different SiC doping concentrations. The fabrication of a high-performance UV photodetector based on a ZnO/4H-SiC heterojunction with high SiC doping concentration of 1018/cm3 was achieved. Its optoelectronic performance was improved compared with either a ZnO UV photodetector or a ZnO/SiC heterojunction photodetector with low SiC doping concentration of 1016/cm3. Heterojunction constructing and energy band bending in the ZnO/SiC interface facilitates the spatial separation of the photogenerated electron-hole pairs and the efficient transport of photoinduced charge carriers, which enhances photocurrent and simultaneously enables a quick time response in the device. In addition, carriers tunneling occurs in the heterojunction interface of ZnO/n+SiC with narrower depletion region width. This study suggests an opportunity for large-area and high-performance nanostructured optoelectronic devices fabrication based on a simple synthesis process and energy band engineering.

Studying the effect of copper on the p-ZnTe/n-AgCuInSe2/p-Si for thin films solar cell applications

A thin film of AgInSe2 and Ag1-xCuxInSe2 as well as n-Ag1-xCuxInSe2 /p-Si heterojunction with different Cu ratios (0, 0.1, 0.2) has been successfully fabricated by thermal evaporation method as absorbent layer with thickness about 700 nm and ZnTe as window layer with thickness about 100 nm. We made a multi-layer of p-ZnTe/n-AgCuInSe2/p-Si structures, In the present work, the conversion efficiency (η) increased when added the Cu and when used p-ZnTe as a window layer (WL) the bandgap energy of the direct transition decreases from 1.75 eV (Cu=0.0) to 1.48 eV (Cu=0.2 nm) and the bandgap energy for ZnTe=2.35 eV. The measurements of the electrical properties for prepared films showed that the D.C electrical conductivity (σd.c) increased with increasing Cu content for AgCuInSe2 thin films. So the electrical conductivity changed from 1 (Ω.cm)-1 to 29.96 (Ω.cm)-1 when x changed from 0.0 to 0.2. The prepared thin films have two activation energies (Ea1 & Ea2) in the temperature ranges of (300-393) K and (303-473) K. The C-V measurements revealed that all prepared heterojunctions were of the abrupt type and the junction capacitance reduced while the width of depletion region and the built-in potential increased with increasing the Cooper content. The current-voltage characteristics under dark condition of AgCuInSe2 heterojunctions, the current-voltage measurements under illumination showed that the performance of heterojunction solar cell improved with increasing Cu content. The result indicated that the prepared solar cell with 0.2 Ag content exhibited the highest efficiency (η = 1.68%) compared to other prepared solar cells.

A Fast Self‐Powered Solar‐Blind Ultraviolet Photodetector Realized by Ga2O3/GaN PIN Heterojunction with a Fully Depleted Active Region

AbstractGa2O3 is a wide bandgap semiconductor suitable for solar‐blind photodetection, but there exist two issues for Ga2O3‐based photodetectors: first, it is difficult to achieve reliable p‐type Ga2O3 and therefore form a homojunction photodetector, and the other is related with the slow response speed of Ga2O3‐based photodetectors. In this work, a self‐powered solar‐blind photodetector with a fast response using a p‐GaN/i‐Ga2O3/n‐Ga2O3 (pin) heterojunction with a fully depleted active region is realized, where i‐Ga2O3 serves as the main light‐absorbing active region. The device exhibits good self‐powered characteristics with a high responsivity of 72 mA W−1, a high photo‐to‐dark current ratio of 18 800, a high specific detectivity of 3.22 × 1012 Jones, and a fast response speed with a rise time/decay time of 7 ms/19 ms, respectively, without an external power supply. A detailed study of the interfacial electronic structure between p‐GaN and i‐Ga2O3 reveals a conduction band offset and valence band offset of 0.16 and 1.37 eV, respectively. Meanwhile, it has a large built‐in potential of 1.03 eV and a wide depletion region width of 235 nm in the i‐Ga2O3 side of heterojunction. It is believed that excellent device performance comes from a suitable energy band structure and wide depletion region.

Eliminating cracking morphology of solution-processed CZTSSe absorbers by Sn-rich composition engineering

Sol-gel method has attracted widespread attention for fabricating highly efficient Cu2ZnSn(S, Se)4 (CZTSSe) solar cells. However, the volume shrinkage of the gel during the baking process will cause severe cracking of CZTSSe films, which results in shunt paths and significantly deteriorates device performance. Herein, an Sn-rich CZTS precursor is proposed to produce high-quality CZTSSe films, which could relieve the shrinkage forces in CZTS precursor film and compensate for Sn loss of CZTSSe absorbers during selenization process. The effects of Sn content on CZTS precursor compactness and the post-selenization process on the crystallization quality of CZTSSe films are thoroughly investigated. Furthermore, the formation of the MoSe2 interfacial layer and the SnSe2 secondary phase can be regulated efficiently. As a result, the separation and collection of carriers are greatly improved as the depletion region width (Wd) of the CZTSSe solar cell is broadened. And the difference between the activation energy (Ea) and band gap (Eg) has decreased, indicating that the carrier recombination loss caused by the deviated Sn content in CZTSSe films has been effectively reduced. Consequently, the efficiency of the CZTSSe device increased from 7.6% to 9.3% through Sn-rich composition engineering. This study elucidates the role of Sn content in the fabrication of high-quality CZTSSe films and advances the development of ambient air-processed CZTSSe solar cells.

Theoretical analysis of GaN-based semiconductor in changing performanc of perovskite solar cell

GaN-based semiconductor has been used in optoelectronics and electronic devices. It is a new research topic at present that how its good electrical properties are integrated together to explore other applications in theory or experiment. In this work, SCAPS-1D software is used to calculate the mechanism of GaN electron transport in an FTO/GaN/(FAPbI<sub>3</sub>)<sub>0.85</sub>(MAPbBr<sub>3</sub>)<sub>0.15</sub>/HTL perovskite solar cell (PSC) structure. The results show that when GaN is used in PSC, the <i>V</i><sub>oc</sub> increases from 0.78 V to 1.21 V, PCE increases from 15.87% to 24.18%, and that the small conduction band cliff formed between GaN and the active layer can improve the efficiency of the cell. Quasi-Fermi level splitting, interfacial electric field, interfacial recombination rate and depletion zone thickness at different doping concentrations s are analyzed. The influences of GaN thickness and doping concentration on open-circuit voltage and other device parameters are investigated. The physical mechanism of GaN as an electron transport layer is discussed. With the increase of the thickness, the <i>J</i><sub>sc</sub> of this solar cell decreases gradually, but the change range is not large (24.13—23.83 mA/cm<sup>2</sup>). The <i>V</i><sub>oc</sub> decreases from 1.30 V to 1.21 V when the thickness of GaN exceeds 100nm, and then keeps stable. The power conversion efficiency changing regularity appears in the form of “pits” —first decreases, then increases, and finally keeps stable, with the highest efficiency being 24.76% and the corresponding GaN thickness being 245 nm. The FF shows a trend, which is first decreasing, then increasing, and finally leveling off. In the case of the doping concentration and thickness change at the same time, during the increase of doping concentration, the <i>J</i><sub>sc</sub> decreases gradually with the increase of thickness, but the overall change range is small, and the open-circuit voltage, filling factor and conversion efficiency all show “pits” changes. When the thickness of GaN is 200 nm, with the concentration of GaN doping increasing, the quasi Fermi level splitting increases, and the strength of the built-in electric field between the active layer and the GaN layer increases, thus providing a greater driving force for carrier separation, resulting in a larger potential difference Δ<i>μ</i>, and thus a larger <i>V</i><sub>oc</sub>. With the increase of doping concentration, the recombination rate of the active layer/GaN layer interface and the recombination rate inside the active layer increase, which leads the value of <i>J</i><sub>sc</sub> to decrease. It is found that the position of the “concave point” of <i>V</i><sub>oc</sub> under the change of GaN thickness is determined by varying the GaN doping concentration, the width of GaN depletion region between GaN/FTO, and the width of GaN depletion region between GaN/active layer determine the width of the whole “pit”. In summary, the cell parameters can be improved by simultaneously changing the thickness and doping concentration of GaN.

Photovoltaic performance optimization of integrated perovskite/organic solar cells based on PM6:Y6 polymer non-fullerene system

Integrated perovskite/organic solar cells (IPOSCs) based on CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>/PM6:Y6(BTP-4F) are successfully prepared through process innovation and thin film optimization technology. The quality of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>/PM6:Y6 mixed films is greatly optimized, and the interlayer ohmic contact is obtained by regulating the additive DIO and annealing treatment. At the same time, the mobility of holes and electrons in the organic layer in the near infrared region are, respectively, 8.3×10<sup>–3</sup> cm<sup>2</sup>/(V·s) and 8.8×10<sup>–3</sup> cm<sup>2</sup>/(V·s), which can match the mobility of holes and electrons in the visible perovskite layer, achieving the carrier transport balance in the microscopic pathway. The device has high short-circuit current density <i>J</i><sub>sc</sub> and high filling factor FF. In addition, by optimizing the mass ratio of polymer non-fullerene system PM6:Y6 to form a film, the density of non-radiation recombination sites and carrier recombination in the film are significantly reduced, making the extraction and transport of electrons and holes more efficient, and providing greater driving force to improve carrier transport. At the same time, a wider depletion region is formed to inhibit carrier recombination and increase the open-circuit voltage <i>V</i><sub>oc</sub>. The short-circuit current density of the optimized integrated solar cell increases to 25.88 A/cm<sup>2</sup>, the open-circuit voltage <i>V</i><sub>oc</sub> increases to 1.18 V, the filling factor FF reaches 80%, the optical response expands to 950 nm, the external quantum efficiency reaches 90% in the visible region, and the optimal energy conversion efficiency is as high as 24.42%. This is one of the highest efficiencies reported in IPOSCs. The results show that it is an effective method to enhance the near-infrared light absorption of perovskite solar cells and improve the performance of IPOSCs by combining the materials in visible region and the polymer non-fullerene system in near infrared region and optimizing the device structure. It lays a theoretical foundation for developing high efficiency IPOSCs in the future.

Assessment of Active Dopants and p-n Junction Abruptness Using In Situ Biased 4D-STEM.

A key issue in the development of high-performance semiconductor devices is the ability to properly measure active dopants at the nanometer scale. In a p-n junction, the abruptness of the dopant profile around the metallurgical junction directly influences the electric field. Here, a contacted nominally symmetric and highly doped (NA = ND = 9 × 1018 cm-3) silicon p-n specimen is studied through in situ biased four-dimensional scanning transmission electron microscopy (4D-STEM). Measurements of electric field, built-in voltage, depletion region width, and charge density are combined with analytical equations and finite-element simulations in order to evaluate the quality of the junction interface. It is shown that all the junction parameters measured are compatible with a linearly graded junction. This hypothesis is also consistent with the evolution of the electric field with bias as well as off-axis electron holography data. These results demonstrate that in situ biased 4D-STEM can allow a better understanding of the electrostatics of semiconductor p-n junctions with nm-scale resolution.

Large‐Scale Depletion of Nighttime Oxygen Ions at the Low and Middle Latitudes in the Winter Hemisphere

AbstractBy analyzing the latitudinal distributions of ionospheric ions observed by the Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions satellite at 670 km altitude in different seasons, we found that the large‐scale depletion of nighttime oxygen ions is prevalent at the low and middle latitudes of winter hemisphere (center ∼ 30°) under different geomagnetic conditions. The latitudinal width of the winter oxygen ion depletion (WOD) region is about 20°–60° at different longitudes, and its upper boundary latitudes are mostly lower than the midlatitude trough (|λ| ≥ 50°) of nighttime hydrogen ions (H+) near the plasmapause. In the WOD region, the density ratio of oxygen and hydrogen ions and that of their neutral densities (O and H) approximately agree with the chemical equilibrium relationship of charge exchange reactions (H + O+ ↔ H+ + O) predicted by previous theory, indicating that the charge exchange reactions are mainly responsible for the large‐scale oxygen ion depletion at the low and middle latitudes in winter hemisphere.

Modeling and characteristics of MWIR HgCdTe APD at different post-annealing processes

Mid-wavelength infrared (MWIR) HgCdTe electron-initiated avalanche photodiodes (e-APDs) have presented excellent performances to resolve and count photons with linear mode. Aiming at low flux, the ROIC noise can be extremely reduced by certain gain, and very low excess noise makes opportunity for noise equivalent photon (NEPh) to be 1. Therefore, the main issue for SNR of HgCdTe APD is gain normalized dark current density (GNDCD) at high reverse bias. In this work, the architecture of multiplication region is modeled and studied. The depth and width of multiplication region are controlled by regulating the p-type doping concentration, ion implantation and post thermal annealing conditions as well. Proper processes can keep the peak electric field away from the implantation damage region, effectively increase the Shockley–Read–Hall (SRH) lifetime, reduce the multiplication region concentration and finally increase the operating voltage. Considered with dark current and gain, depletion region (I region) width is optimized and characterized to be 3–3.6 μm when I region concentration is ∼1 × 1015 cm−3 in our case. The GNDCD of MW APD (cut off wavelength ∼5.16 μm @80 k) is less than 10−6 A/cm2@≤-10 V, with avalanche gain of ∼1570@-9.8 V. The excess noise factor (F) is measured to be 1–1.4 by noise power spectral density (PSD). The NEPh value is less than 5 photons with gain up to ∼280 for MW 128 × 128 HgCdTe APD array. Simulation results anticipate that GNDCD can be further reduced by decreasing the doping concentration of I region to below 5 × 1014 cm−3. Furthermore, increasing the p-type doping concentration and band gap will significantly reduce GNDCD below to ∼10−10 A/cm2@-10 V for 4.22 μm Hg1-xCdxTe (x = 0.332) APD.

Li/Ag Co‐Doping Synergistically Boosts the Efficiency of Kesterite Solar Cells Through Effective SnZn Defect Passivation

AbstractDespite the tremendous progress in the efficiency of Cu2ZnSn(S,Se)4 (CZTSSe) photovoltaic devices, open‐circuit voltage (Voc) deficit, mainly related to the SnZn‐related defects in the absorber, still remains one of the key issues that hinders the cell performance. To overcome this hurdle, here a facile synergistic post‐deposition treatment (PDT) strategy in CZTSSe family via AgF‐PDT after LiF‐PDT in the photovoltaic absorber to suppress SnZn defects, and thus, to promote the Voc and power conversion efficiency (PCE), is reported. Furthermore, a mechanism for improving device efficiency of CZTSSe cell is also proposed. The in‐depth investigation results demonstrate that Li/Ag co‐doping reduces the band tailing characteristic, enlarges the depletion region width, and enhances the carrier transport and collection, resulting in a lower bulk and interface recombination. More importantly, Li/Ag co‐doping strategy provides an effective method for SnZn defect passivation, thereby prolonging minority carrier lifetime in the ensuing devices and leading to enhancement in device performance. Correspondingly, the resulting Li/Ag co‐doped device delivers a champion efficiency of 12.58% with an impressive Voc of 507 mV. This work explores an effective strategy to kill the SnZn‐related defects, thereby overcoming the problems associated with the Voc deficit and lower cell efficiency in Kesterite‐based photovoltaic devices.

Understanding efficiency improvements of betavoltaic batteries based on 4H-SiC, GaN, and diamond

Wide-bandgap semiconductors are more advantageous for betavoltaic batteries due to their high conversion efficiency and strong radiation resistance. However, there has been little comprehensive analysis of how wide-bandgap semiconductors lead to efficiency improvements. In this work, we proposed a simulation model to predict the output performance of betavoltaic batteries based on 4H-SiC, hexagonal-GaN, and diamond, in which the Monte Carlo code and COMSOL Multiphysics software were combined. The energy deposition of a 63Ni source in semiconductors and the electrical characteristics of p–n junctions were investigated and compared. Our simulation results showed that the mass density and atomic number of semiconductor materials will cause the difference in energy deposition distribution, further leading to the different electron–hole pair generation rates. Then, the internal efficiency of batteries is co-determined by the energy band structure, depletion region width, built-in potential barrier, and minority carrier lifetime. The batteries based on wide-bandgap semiconductors can achieve the larger open-circuit voltage, further leading to higher efficiency. Additionally, to optimize the energy converter structure, the output parameters were calculated with a variation of doping concentrations and thicknesses of each region. Under the irradiation of a 63Ni source, the diamond-based battery with a p–n junction structure has the highest internal efficiency of 31.3%, while the GaN-based battery has the lowest one (16.8%), which can be attributed to the larger carrier recombination rate.

The Effect of Absorber Stoichiometry on the Stability of Widegap (Ag,Cu)(In,Ga)Se2Solar Cells

(Ag,Cu)(In,Ga)Se2solar cells with bandgaps of ≈1.45 eV with a large spread in absorber stoichiometry are characterized with the intention of assessing the effect of composition on the stability of the devices. This material is observed to have a poor diffusion length, leading to very strong dependence upon the depletion region width for charge carrier collection. The depletion width is observed to depend strongly upon the stoichiometry value and shrinks significantly after an initial period of dark storage. It is also seen that the depletion width can be varied strongly through light‐soaking and dry‐heat treatments, with prolonged annealing leading to detrimental contraction and light soaking leading to expansion which increases current collection. The extent of depletion width variation in response to the treatments is also clearly linked to absorber stoichiometry. Consequently, the device performance, particularly the current output, exhibits a stoichiometry dependence and is considerably affected after each round of treatment. Possible causes of this behavior are discussed.

Modeling and optimization of GaN-based betavoltaic batteries: Comparison of p–n and p–i–n junctions

Nuclear battery is a promising long-life power source. Selecting semiconductors with high limit efficiency and appropriate device structures effectively improves their output performance. In this work, a GaN-based (hexagonal) betavoltaic battery with Ni63 source was simulated by Monte Carlo codes and COMSOL Multiphysics, and the energy converters, including p–n junction and p–i–n junction, were compared and optimized. We analyzed the effects of thickness and doping concentration of each region on the battery performances. The p-region and n-region thickness and doping concentration of the p–n junction-based battery are 0.5, 9.5 µm, 1017 cm−3, and Nd = 1016 cm−3, which can achieve 3.77% conversion efficiency, and the short-circuit current density, open-circuit voltage, and maximum output power density are 0.074 µA/cm2, 2.01 V, and 0.125 µW/cm2, respectively. For the p–i–n junction-based battery, when the thickness and the doping concentration of p-region, i-region, and n-region are 0.5, 3, 6.5 µm, 1017, 1014, and 1016 cm−3, respectively, the conversion efficiency, short-circuit current density, open-circuit voltage, and maximum output power density are 5.03%, 0.099 µA/cm2, 2.0 V, and 0.167 µW/cm2, respectively. By comparing the output parameters of the two types of batteries, the results indicate that the p–i–n junction has a wider depletion region and better output performance compared with the p–n junction.

Normally-off AlGaN/GaN heterojunction field-effect transistors with in-situ AlN gate insulator

AlGaN/GaN heterojunction field-effect transistors (HFETs) with p-GaN cap layer are developed for normally-off operation, in which an in-situ grown AlN layer is utilized as the gate insulator. Compared with the SiN x gate insulator, the AlN/p-GaN interface presents a more obvious energy band bending and a wider depletion region, which helps to positively shift the threshold voltage. In addition, the relatively large conduction band offset of AlN/p-GaN is beneficial to suppress the gate leakage current and enhance the gate breakdown voltage. Owing to the introduction of AlN layer, normally-off p-GaN capped AlGaN/GaN HFET with a threshold voltage of 4 V and a gate swing of 13 V is realized. Furthermore, the field-effect mobility is approximately 1500 cm2⋅V−1⋅s−1 in the 2DEG channel, implying a good device performance.

Interface Engineering of CZTS/TiO2Heterojunction Using Wide‐Bandgap Ga2O3Passivation Interlayer for Efficient Charge Extraction

The greatest challenge for further improving the efficiency of Cu2ZnSnS4(CZTS) solar cells is the high open‐circuit voltage (VOC) loss owing to nonradiation interface recombination. Controlling interfacial defect states and hence eliminating interface‐dominated recombination are imperative for device performance to achieve better charge extraction and collection. In this aspect, interface passivation is an effective way to resolve this issue. An ultrawide‐bandgap Ga2O3film is inserted between CZTS absorber and TiO2electron transport layer to passivate the electrically active interface trap states. The induced field‐effect passivation due to the existence of an additional field of Ga2O3interlayer widens the depletion region width and cures the interfacial defect density. The significant photoluminescence quenching observed after inserting Ga2O3at the CZTS/TiO2heterojunction implies the effective injection of charge carriers from the CZTS absorber to TiO2layer owing to reduced interface defect density. Meanwhile, the substantial decrement in dark current and response time of device with passivated interface further advocates the findings. Herein, a route to understand the variation in interfacial electrical properties after inserting a thin dielectric layer at the interface is provided, which can be beneficial for the further study of CZTS‐based optoelectronic device applications.

Self-Powered Sb2S3 Thin-Film Photodetectors with High Detectivity for Weak Light Signal Detection.

Photodetectors (PDs) for weak light signal detection have wide applications for optical communication and imaging. Antimony sulfide (Sb2S3) as a nontoxic and stable light-sensitive material becomes a promising candidate for weak light PDs, which are developing in the direction of high response, high speed, and low cost. Herein, a self-powered Sb2S3 PD with the structure of FTO/TiO2/Sb2S3/Au is developed to achieve weak light detection for 300-750 nm visible light. We control the Sb2S3 thickness with about 460 nm to match depletion region width (438 nm) and obtain an excellent photoresponsivity and 3 dB bandwidth. Furtherly, we prepare pyramid structure polydimethylsiloxane (PDMS) on the illuminating surface to enhance the performance of weak light detection by light-trapping effects. The photocurrent of Sb2S3 PD with 20 μm-sized PDMS texture achieves 13.6% improvement compared with the control one. Under weak 530 nm light illumination of 1 μW cm-2, the self-powered Sb2S3 PD with PDMS achieves high responsivity (3.41 A W-1), large detectivity (2.84 × 1013 Jones), and ultrafast speed (15 μs). The present Sb2S3 PD and light-trapping strategy are expected to provide an alternative to future commercial weak light detection applications.