Pn Heterojunction Research Articles

Self‐Powered and Vis‐Infrared Broadband Gr/InSe/MoTe2 Heterostructure Photodetectors with Ultra‐Fast Response and Low Dark Current

AbstractSelf‐powered photodetection devices, which meet the requirement of environmental sustainability, are widely designed by PN heterojunctions. The design of the semiconductor/metal interface is vital in PN‐junction devices. In particular, the elevated potential barrier at the metal/semiconductor interface impedes efficient carrier transport. Therefore, optimizing the semiconductor/metal interface for the PN junction, either by reducing the interface barrier or leveraging the built‐in electric field within the Schottky junction, holds significant importance in enhancing the performance of PN‐junction devices. In this study, an InSe/MoTe2 Type‐II PN heterojunction photodetector is constructed, with graphene (Gr) and gold (Au) serving as electrodes in contact with InSe and MoTe2, respectively. Benefiting from the reduced barrier in Au/InSe interfaces and the built‐in electric field formed at the InSe/MoTe2 and MoTe2/Au interfaces in the same direction, the device achieves an ultra‐fast photoresponse speed of 14 µs and an ultra‐low dark current of 8.5 × 10⁻¹⁴ A at zero bias. Furthermore, the device exhibits a remarkable light on/off ratio up to 105 and achieves broad‐spectrum photodetection ranging from the visible to infrared wavelength. This research highlights the enormous potential of the Gr/InSe/MoTe2 van der Waals heterostructure in the realms of self‐powered photodetection, imaging, and optical communication.

Effects of NiO doping and trench wall tilt on Ga2O3 PiN diodes performance

Gallium Oxide (Ga2O3) is a promising material for next-generation power semiconductors due to its wide bandgap (∼4.9 eV), high Baliga's figure of merit (FOM) (3444 W/cmK), and high breakdown field (Ec, 8 MV/cm). To achieve high blocking and low leakage current, research has been conducted on PN heterojunctions and bevel structures. In this paper, we performed simulations using Sentaurus TCAD to investigate the impact of NiO doping concentration and NiO's trench tilt angle on the electrical characteristics of NiO/Ga2O3 PiN diodes with trench NiO. As the NiO doping concentration increased, the resistance decreased from 21.5 to 7.5 mΩcm2, and we observed the expansion of depletion from NiO to the NiO/Ga2O3 interface. Furthermore, we confirmed a reduction in resistance and a change in breakdown voltage with an increase in NiO trench tilt. By understanding the optimal angle to mitigate the concentration of high electric fields in the edge region, we anticipate the fabrication of stable Ga2O3 PiN diodes.

Self-Powered Photodetectors Based on InGaN/PdO PN Heterojunctions for Visible Light Communication

Self-Powered Photodetectors Based on InGaN/PdO PN Heterojunctions for Visible Light Communication

Construction of one-dimensional pn heterojunction TiO2/CuO composite with hierarchical structure and its dual efficient inactivation of Escherichia coli

Construction of one-dimensional pn heterojunction TiO2/CuO composite with hierarchical structure and its dual efficient inactivation of Escherichia coli

CuS@MoS2 p[sbnd]n heterojunction photocatalyst integrating photothermal and piezoelectric enhancement effects for tetracycline degradation

Photocatalysis is an environmentally friendly and low-cost technology for the degradation of pollutants. In addition to the construction of heterojunction which may decrease the recombination of charge carriers and extend the photo-response range, the utilization of piezoelectricity and photothermal conversion also provides the promising routes to improve the photocatalytic performance. Herein, a CuS@MoS2 heterostructure was developed to simultaneously meet the needs of these enhancement mechanisms. The formation of pn heterojunction was confirmed and the associated energy band diagram was constructed with band gaps of CuS and MoS2 as 1.56 and 1.80 eV, respectively. For the degradation of tetracycline, it was demonstrated that the inherent piezoelectric property of MoS2 surface enhanced the piezocatalytic activity by inducing an electric field to aid charge separation. The heat generated by illumination raised the photocatalytic reaction rate by supplying extra energy to carriers. The CuS@MoS2 heterostructure exhibited significantly better catalytic performance than the individual CuS or MoS2 due to the formation of pn heterojunction. Furthermore, the combination of piezoelectricity and photothermal conversion also led to a significant synergistic effect, achieving a degradation efficiency of over 95% within 30 min. As compared to the conditions under ultrasonic vibration, visible light irradiation and visiblenearinfrared light irradiation alone, the combination of visiblenearinfrared irradiation and ultrasonic vibration could lead to 96, 205 and 81% enhancement. This work provides valuable insights into the design of novel heterojunction photocatalysts integrating the piezoelectric and photothermal enhancement effects.

Enhancing performance of SnS2 based self-powered photodetector and photocatalyst by Na incorporation

Sn and S are environmentally friendly elements that are abundant in nature. The SnS2 compound formed with these elements has intrinsic n-type electrical conductivity and a direct forbidden band gap of ∼2.2 eV. Therefore, it is a very promising compound for visible light optoelectronic applications. In this study, SnS2thin films were coated on p-Si substrates and pn heterojunction structures were obtained. By adding certain amounts of Na element to SnS2, the photosensitivity of the heterojunction devices increased tremendously and reached a high value of 3.2 × 104 under zero bias condition. It was observed that the prepared devices had excellent speeds and stability with rise and decay times of as low as 28 m s and 23 m s. Moreover, the devices were found to be sensitive to visible light even at ultra-low light intensity of ∼0.3 μW/cm2. Furthermore, the responsivity and specific detectivity values of the prepared photodetectors reach very high values of 11 A/W and 8.4 × 1013 Jones at this low light intensity. The NEP value drops to a low level of 2.7 × 10−15 WHz −1/2. In addition, the photocatalytic properties of Na-doped and undoped SnS2 compound were also examined under visible LED light. Compared to undoped samples, photocatalytic efficiency increased by ∼42 % in Na-doped SnS2 thin films. The findings clearly reveal that Na improves both photodetector device performance and the photocatalytic effect of the SnS2 semiconductor.

In situ growth of BiVO4–Bi2O3 p-n heterojunction nanocomposite via facile green combustion method: Efficient photocatalytic activity under visible light, photoluminescence and biosensing applications

The easiest and simplest green combustion approach was successfully used to synthesize the pn Heterojunction BiVO4/Bi2O3 nanocomposites (NCs) with efficient visible light activity. Different stoichiometric ratios of butea monosperma leaf powder were used as the green fuel. Using XRD, SEM, EDAX, FTIR, UV–visible, and PL spectroscopy, the phase and surface structure, composition, and optical properties of synthesized NCs are characterised. In comparison to other ratios, it was found that the 1:1.5 ratio of BiVO4/Bi2O3 NCs exhibits good photocatalytic performance for the degradation of rose bengal dye. The outcome demonstrated that the formation of a p-n heterojunction between p-type Bi2O3 and n-type BiVO4 is responsible for the improved photocatalytic activity. It resulted from the separation of electron and hole pairs and the improvement of the interfacial charge transfer efficiency, both of which were made possible by the heterojunction. In addition, the BVO 15 photocatalyst exhibits good stability across 4 degradation cycles. The glassy carbon electrode (GCE) was modified with BVO NCs for the electrochemical detection of dopamine (DA). By using CV and LSV, the electrochemical behaviour of the fabricated electrode was examined. The outcomes demonstrate that BVO NCs have strong electrocatalytic activity. The limit of detection (LOD) was determined to be 33 μM. The current work is also a beneficial effort for developing new visible light photocatalysts with heterojunction architectures and biosensors.

Ferroelectric BaTiO3 Nanoparticles Embedded at the p–n Heterojunction Interface Improves the Carrier Transport in Kesterite Solar Cells

AbstractThe built‐in field (Ebi) is a key factor for the dynamic of carrier transport in the heterojunction interface, thus determining the photovoltaic performance of the solar cell, such as Cu2ZnSn(S,Se)4 (CZTSSe) cell. It is critical to improve the carriers' transport across the pn heterojunction for the fabrication of highly efficient solar cells. In this work, the large electric field of ferroelectric BaTiO3 nanoparticles (BTO NPs) is used to tailor the carrier transport in the CZTSSe solar cells by embedding BTO NPs into the interface of CZTSSe/CdS heterojunction. It is very surprising that a polarization electric field (EP) with the same direction of Ebi synergically enhances carrier transport greatly and increases the PCE by 20.6%. Further study on the mechanism discloses that BTO NPs reduce the work function of CZTSSe and CdS and form interfacial dipoles at their interface, which is conducive to the photogenerated electrons to be collected by the electron transport layer. This strategy also works well on other thin film solar cells and gives a new aspect of strengthening the carrier transport between p–n heterojunction.

Enhancement of photodetection performance of Ga2O3/Si heterojunction solar-blind photodetector using high resistance homogeneous interlayer

Creating homojunctions using Ga2O3 material presents a significant challenge, primarily because of the inherent difficulty in achieving stable p-type Ga2O3. The pn heterojunctions based on n-Ga2O3 materials offer a promising alternative for developing solar-blind photodetectors. In this work, our strategy is to fabricate a n-Ga2O3/p-Si heterojunction solar-blind photodetector with interface layers of high resistance and low resistance through using a magnetron sputtering system. The results indicate that a Ga2O3 layer with high resistance as an interface layer contributes to broadening the width of space charge region of this pn heterojunction, resulting in the enhancement of photodetection responsivity (61.7 mA/W @-5 V). Furthermore, the pn heterojunction photodetector exhibits a photo-response to 254 nm UV light at zero bias voltage, showcasing robust stability. This suggests significant potential for applications in the challenging environments. The synergistic blend of the enhanced photodetector performance and the well-established technology of Si integrated circuits is generating considerable enthusiasm.

Redeeming the photocatalytic potential of CuWO4 incorporating Ag6Si2O7 via S-scheme PN heterostructure

Water pollution and energy crisis are deemed the most prevalent issues of contemporary decades, and enhanced efforts to counteract these issues via semiconductor photocatalyst engineering are among the best-proposed solutions. Semiconductor photocatalysts could effectively transform clean sunlight into chemical energy, thereby facilitating the breakdown of organic dyes. Herein, we demonstrate the PN heterojunction S scheme photocatalyst Ag6Si2O7/CuWO4 via the facile hydrothermal method. The Ag6Si2O7/CuWO4 heterostructure discerns the broadening of the absorption spectrum and enhanced carrier separation owing to the interfacial process at the interface. Both these aspects work as a stimulus regarding the photocatalytic properties and add versatilities to the effective utilization of carriers. The performance of different ratios of Ag6Si2O7 and CuWO4 in Ag6Si2O7/CuWO4 composite was monitored via photocatalytic degradation of Rhodamine B and Methylene Blue under visible irradiation. About 97.50% degradation efficiency for RhB was reached in 50 minutes at a 1:5 molar ratio (AgCW-E). The degradation constant rate of AgCW-E for RhB and MB was 21.12 and 26.13 times higher than pristine, respectively. Based on trapping experiments and electron spin resonance spectra, it was determined that the photogenerated holes (h+) and •O2- played a crucial role as active species in the photocatalytic degradation of RhB. The synthetic substances additionally demonstrated great promise for recycling. The present study delivers an innovative perspective on developing a more potent Ag6Si2O7/ CuWO4 nano heterojunction photocatalyst that can capture visible light.

Multilevel and Low-Power Resistive Switching Based on pn Heterojunction Memory

Multilevel and Low-Power Resistive Switching Based on pn Heterojunction Memory

Using thin-film transistor with thick oxygen-doped Si–Zn–Sn–O channel and patterned Pt/NiO capping layer to enhance ultraviolet light sensing performance

Improving the photodetection performance of thin-film transistor (TFT)-based UV photodetectors (UVPDs), using thick channel layers to promote photocurrent (I ph) or using thin channel layers to suppress dark current (I dark) is typically a trade-off. In this work, UVPDs based on oxygen-doped Si-Zn-Sn-O (SZTO) TFT with a stack of Pt/NiO capping layers (CLs) to release the trade-off between I dark and I ph are demonstrated. The Pt CL creates a wide depletion region in the channel layer to allow the use of thick channels, but still maintains low I dark, while the NiO CL forms a pn heterojunction to provide additional photogenerated carriers and enhance I ph under UV irradiation. Experimental results show that the proposed 95 nm-thick oxygen-doped SZTO TFT with a stack of Pt/NiO dual CLs exhibits an excellent photoresponsivity of 2026 A W−1 and photosensitivity of 9.3 × 107 A A−1, which are about 76× and 82.5× higher than a conventional 45 nm-thick SZTO TFT under 275 nm UV irradiation.

High-performance CsSnBr<sub>3</sub>/Si PN heterojunction photodetectors prepared by pulsed laser deposition epitaxy

Halide perovskite semiconductors have outstanding physical properties such as high light absorption coefficient, large carrier diffusion length, and high photoluminescence quantum efficiency, and demonstrate significant potential applications in optoelectronic devices such as photodetectors and solar cells. However, the toxicity and environmental instability associated with lead-based perovskites significantly limit their applications. An attractive solution is substituting tin for lead in perovskites and growing high-quality tin-based perovskite films. In this study, we adopt the pulsed laser deposition method to achieve the epitaxial growth of CsSnBr<sub>3</sub> films on silicon substrates. The morphologies, optical and electrical properties of the CsSnBr<sub>3</sub> films, as well as the CsSnBr<sub>3</sub>/Si heterojunction detectors, are comprehensively investigated with various characterization techniques, including XRD 2<i>θ</i>-<i>ω</i> and <i>φ</i> scans, atomic force microscope, scanning electron microscope, photoluminescence and time-resolved photoluminescence spectroscopy, and Hall electrical measurements. The results indicate that such a CsSnBr<sub>3</sub> film grows epitaxially onto the silicon substrate via a face-to-face mode. Interestingly, an unusual temperature-dependent bandgap increase is found to be due to the high electron effective mass of CsSnBr<sub>3</sub>. The CsSnBr<sub>3</sub> film shows the P-type semiconductor behavior with a high mobility of 122 cm²/(V·s), enabling the formation of an ideal Type-II heterojunction with the silicon substrate. The CsSnBr<sub>3</sub>/Si semiconductor heterojunction detector exhibits distinctive heterojunction PN diode characteristics in the dark and a pronounced photoresponse under illumination. At zero bias, the detector displays a switch ratio exceeding 10<sup>4</sup>, responsivity of 0.125 mA/W, external quantum efficiency of 0.0238%, detectivity (<inline-formula><tex-math id="Z-20240301150440">\begin{document}$D^* $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231645_Z-20240301150440.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231645_Z-20240301150440.png"/></alternatives></inline-formula>) of 2.1×10<sup>9</sup> Jones, response time 3.23 ms, and recovery time of 4.87 ms. Under a small bias of –1 V, the switch ratio decreases to 50, but responsivity and external quantum efficiency increase by 568 times. The detectors can maintain self-powered operation state with a high switch ratio of 10<sup>4</sup>, millisecond-level response time and millisecond-level recovery time. In conclusion, this work presents a self-powering, high-performance photodetector based on CsSnBr<sub>3</sub> epitaxial films integrated with silicon substrates.

Enhanced photoelectrochemistry water splitting based on the bi-piezoelectric Z-scheme pn heterojunction of an n-CdTe/p-ZnO nanorods array

An n-type Cd-excess CdTe (n-CdTeCd)/p-type Sb-doped ZnO nanorods (p-ZnONR,Sb)/indium tin oxide photocathode with a bi-piezoelectric Z-scheme pn heterojunction is prepared by hydrothermal method and electrodeposition for photoelectrochemistry (PEC) water splitting. At 0 V vs RHE under 100 mW cm−2 Xe lamp illumination in 0.5 M aqueous Na2SO4 stirred at 1500 rpm, the photocurrent density, H2 (O2 evolved at a Pt anode) yield, and the apparent Faradaic efficiency for this photocathode are −3.86 mA cm−2, 58.5 (28.6) μmol cm−2 h−1 and 84.7%, respectively. After examining the other similar semiconductor combinations of n-CdTeCd or p-type Te-excess CdTe (p-CdTeTe) with n-type ZnO nanorods (n-ZnONR) or p-ZnOSb,NR, the co-effects of bi-piezoelectric and pn-junction electric fields on the separation and transfer of photogenerated charges for PEC water splitting are discussed in detail. This work may help to better understand various heterojunctions and the electric-field-modulated photogenerated charges’ separation and transfer for the development of relevant fields.

Activating p-type conduction and visible transparency in delafossite CuAlO2 films: The critical role of the copper valence state transition

P-type oxide semiconductors with high p-type conductivity and visible transparency are highly desired for various electronic devices. However, achieving these two demands is challenging due to the localized oxygen 2p orbitals and compensating donors in oxides. This is seen in the representative delafossite CuAlO2, despite tremendous theoretical and experimental efforts in perfecting the lattice quality and physical properties. Here, we reveal the critical role of the copper valence state transition in activating high p-type conduction and visible transparency in CuAlO2. A two-step synthesis strategy is developed to fabricate c-axis-oriented CuAlO2 films with similar crystallinity but with very different Cu2+/Cu+ proportions on sapphire substrates. In combination with structural and transport characterizations, this study distinguishes the key impact of the cooper valence state from the more commonly noticed lattice crystallization, for simultaneously achieving a room-temperature p-type conductivity of >1 S/cm and visible transmittance of >75 %. We further demonstrate that the strategy of obtaining high-performance CuAlO2 films is applicable to n-type SiC substrates for fabricating pn heterojunction diodes with a rectifying ratio of 106. This study provides critical insights into designing and synthesizing high-performance p-type oxide semiconductors.

Fast Response, High Spectral Rejection Ratio, Self-Filtered Ultranarrowband Photodetectors Based on Perovskite Single-Crystal Heterojunctions.

Narrowband photodetectors have wide application potential in high-resolution imaging and encrypted communication, due to their high-precision spectral resolution capability. In this work, we report a fast response, high spectral rejection ratio, and self-filtered ultranarrowband photodetector with a new mechanism, which introduces bulk recombination by doping Bi3+ and cooperates with surface recombination for further quenching photogenerated charges generated by short-wavelength-light excitation in perovskite single-crystal. A perovskite film focused on collecting charges is fabricated on the single crystal by a lattice-matched solution-processed epitaxial growth method. Due to the formation of PN heterojunctions, a narrowband photodetector in this mechanism has remarkable spectral selectivity and detection performance with an ultranarrow full width at half-maximum (FWHM) of 7.7 nm and a high spectral rejection ratio of 790, as well as a high specific detectivity up to 1.5 × 1010 Jones, a fast response speed with a rise time and fall time of ∼8 and 137 μs. The ultrafast and ultranarrow spectra response of self-filtered narrowband photodetector provides a new strategy in high-precision and high-resolution photoelectric detection.

Shear horizontal wave in a p-type Si substrate covered with a piezoelectric semiconductor n-type ZnO layer with consideration of PN heterojunction effects

Shear horizontal wave in a p-type Si substrate covered with a piezoelectric semiconductor n-type ZnO layer with consideration of PN heterojunction effects

An efficient MSM UV photodetector with an ultra-low dark current enhanced by a back to back TiO2/PbTiO3 PN heterojunction

A TiO2 MSM UV photodetector has been extensively researched and exhibits many good properties such as stability and a large ratio of light to dark current. However, it suffers from a high dark current and slow response and recovery. In this work, an MSM UV photodetector based on a TiO2/PbTiO3 heterojunction was fabricated by a sol-gel method. Spontaneous polarization of ferroelectric perovskite PbTiO3 can deplete carriers and accelerate the separation and transport of photo-generated carriers. The photodetector showed enhanced performances, including an ultra-low dark current (1.146 19 × 10−11 A), an improving ratio of light to dark current, as well as short response and recovery times (decreasing to 65 and 81 ms). These results indicate the potential in the combination of ferroelectric perovskite PbTiO3 with traditional wide bandgap semiconductor materials to fabricate high-performance UV photodetectors.

A highly sensitive TiO2-based molecularly imprinted photoelectrochemical sensor with regulation of imprinted sites by Photo-deposition

Molecularly imprinted photoelectrochemical sensors (MIPES) have gained significant attention in the detection field due to their high selectivity and accuracy. However, their sensitivity still needs improvement. Here we developed a TiO2-based MIPES (TiO2 NRs/NiOOH/rMIP) to detect ciprofloxacin (CIP). We identified the photoactive sites of TiO2 by NiOOH photo-deposition and anchored the imprinted sites on the photoactive sites by complexation between CIP and NiOOH. By regulating the imprinted sites, the photocurrent difference before and after the addition of CIP increases and the detection sensitivity of CIP is improved. Moreover, a PN heterojunction is formed between TiO2 and NiOOH, which enables rapid transfer of photoexcited holes and electrons to different semiconductors under the built-in electric field. This leads to improved photoactivity of TiO2 and further increases the sensitivity of MIPES. Compared with sensors prepared by the traditional electro-polymerization CIP and Molecularly imprinted polymers (TiO2 NRs/NiOOH/eMIP), TiO2 NRs/NiOOH/rMIP as constructed in this work displays higher sensitivity, wider linear detection range, and lower limit of detection (LOD). Additionally, TiO2 NRs/NiOOH/rMIP shows good selectivity, stability, and recovery rate, and has a promising application prospect in the actual detection of antibiotics.

An experimental study for thermal sensing applications of PP and PN heterojunctions fabricated in the same architecture and under the same conditions

In this research, Ni/p-GO@Fe3O4/p-Si (P–P) and Ni/ p-GO@Fe3O4/n-Si (P–N) heterojunctions (HJs) were constructed under the same conditions. Current–voltage (I–V) measurements of devices over a wide temperature range were investigated. Thermionic emission theory was used to evaluate the temperature-dependent I–V characteristics. The ideality factor (n), barrier height (Φ), rectification ratio (RR) and turn-on voltage (V 0), which are the main HJ parameters of the HJs, were determined as a function of temperature and it was seen that all parameters were dependent on temperature. The n, RR, and V 0 values for both devices decreased with increasing temperature, while Φ increased. This was attributed to the inhomogeneity between p-GO@Fe3O4 and Si. The thermal sensitivity (S) and activation energy of both devices were calculated and it was seen that S decreased linearly with increasing current. Furthermore, the highest sensitivity and the lowest activation energy values were determined as 1.35 mV K−1 and 0.79 eV, respectively for P–P HJ. These values were calculated as 0.97 mV K−1 and 0.66 eV for P–N HJ, respectively.