P-n Junction 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.

Investigation on indium concentration in two-terminal tandem indium gallium nitride solar cells by SCAPS-1D

Indium gallium nitride (InGaN) thin-film solar cell is a promising photovoltaic (PV) device. InGaN’s bandgap is tunable from 0.7 to 3.4 eV and it exhibits a high absorption coefficient exceeding 105 cm−1. Besides, InGaN solar cells can be used in tandem configuration, to effectively absorb the solar spectrum. Previous works found that increased indium (In) concentration leads to inverse relationship between open-circuit voltage (Voc) and power conversion efficiency (PCE) of the solar cell. This leads to deleterious device performance. This study aims to assess the performance of two-terminal InGaN tandem solar cells using SCAPS-1D simulation software. The findings revealed maximum short-circuit current density (Jsc) of 26.19 mA cm−2, open-circuit voltage (Voc) of 2.13 V, fill factor (FF) of 89.68%, and PCE of 30.17% from the tandem device. The results indicate that higher In concentration enhances light absorption and the overall PCE, with tandem cells outperforming single-junction cells. This study makes a valuable contribution to the advancement of high-efficiency solar technology based on InGaN.

Preparation and Photocatalytic Performance of In2O3/Bi2WO6 Type II Heterojunction Composite Materials.

Bismuth-based photocatalytic materials have been widely used in the field of photocatalysis in recent years due to their unique layered structure. However, single bismuth-based photocatalytic materials are greatly limited in their photocatalytic performance due to their poor response to visible light and easy recombination of photogenerated charges. At present, constructing semiconductor heterojunctions is an effective modification method that improves quantum efficiency by promoting the separation of photogenerated electrons and holes. In this study, the successful preparation of an In2O3/Bi2WO6 (In2O3/BWO) II-type semiconductor heterojunction composite material was achieved. XRD characterization was performed to conduct a phase analysis of the samples, SEM and TEM characterization for a morphology analysis of the samples, and DRS and XPS testing for optical property and elemental valence state analyses of the samples. In the II-type semiconductor junction system, photogenerated electrons (e-) on the In2O3 conduction band (CB) migrate to the BWO CB, while holes (h+) on the BWO valence band (VB) transfer to the In2O3 VB, promoting the separation of photoinduced charges, raising the quantum efficiency. When the molar ratio of In2O3/BWO is 2:6, the photocatalytic degradation degree of rhodamine B (RhB) is 59.4% (44.0% for BWO) after 60 min illumination, showing the best photocatalytic activity. After four cycles, the degradation degree of the sample was 54.3%, which is 91.4% of that of the first photocatalytic degradation experiment, indicating that the sample has good reusability. The XRD results of 2:6 In2O3/BWO before and after the cyclic experiments show that the positions and intensities of its diffraction peaks did not change significantly, indicating excellent structural stability. The active species experiment results imply that h+ is the primary species. Additionally, this study proposes a mechanism for the separation, migration, and photocatalysis of photoinduced charges in II-type semiconductor junctions.

Operation mode-switchable photodetector with local-floated gate of pn junction

Operation mode-switchable photodetector with local-floated gate of pn junction

Performance study of GaN-based betavoltaic nuclear batteries with 3D interfaces

This study presents a design of a 3D interface simulation model featuring an inverted pyramid structure. Our objective is to forecast the performance of GaN-based betavoltaic nuclear batteries with the PN junction 3D interface structures comparing a practical machining process. Initially, we computed the electron-hole pairs (EHPs) generation rate in GaN materials irradiated by both 63Ni and 147Pm sources using Geant4. Furthermore, we employed COMSOL Multiphysics, a finite element analysis software, to simulate the EHPs transport phenomena within the battery and investigate the influence of structural parameters on the output performance. Despite maintaining thicknesses of the P- and N-regions and consistent doping concentrations (Hp-GaN, Hn-GaN, Na, and Nd) as constants, the simulation results revealed notable disparities in the short-circuit current density (Jsc), open-circuit voltage (Voc), and maximum output power density (Pmax) among batteries irradiated with various radioactive sources. Subsequently, we investigated the output performance of the nuclear battery by altering parameters such as the number of inverted pyramid structures, junction depth, and type of radioactive source. Our investigation revealed that selecting 63Ni as the radioactive source, with Na at 1017 cm−3, Nd at 1014 cm−3, a junction depth of 0.1 μm, and inverted pyramid structures of 25, resulted in the following battery performance parameters: a short-circuit current density (Jsc) of 0.648 μA/cm2, an open-circuit voltage (Voc) of 2.3481 V, and a maximum output power density (Pmax) of 1.2949 μW/cm2. Substituting the radioactive source with 147Pm, the average short-circuit current density, Jsc, increased to 56.865 μA/cm2, and the maximum output power density, Pmax, increased to 94.975 μW/cm2, It's a significant enhancement in output performance.

A hBN/Ga2O3 pn junction diode.

The development of next-generation materials such as hBN and Ga2O3 remains a topic of intense focus owing to their suitability for efficient deep ultraviolet (DUV) emission and power electronic applications. In this study, we combine p-type hBN and n-type Ga2O3, forming a pseudo-vertical pn hBN/Ga2O3 heterojunction device. Rectification ratios > 105 (300K) and [Formula: see text]400 (475K) are observed and are amongst the highest values reported to date for ultra-thin hBN-based pn junctions. The measured current under forward bias is ~2mA, which we attribute to the shallow Mg acceptor level (60 meV), and 0.2 µA at -10V. Critically, device performance remains stable and highly repeatable after a multitude of temperature ramps to 475K. Capacitance-voltage measurements indicate widening the depletion region under increasing reverse bias voltage and a built-in voltage of 2.34V is recorded. The hBN p-type characteristic is confirmed by Hall effect, a hole concentration of [Formula: see text] cm-3 and mobility of 24.8 cm2/Vs is achieved. Mg doped hBN resistance reduces by >108 compared to intrinsic material. Future work shall focus on the optical emission properties of this material system.

Finite Element Analysis of LED Heat Dissipation Performance Based on Graphene Composites

Abstract With the gradual development of integrated circuits to thin, high-performance and versatile of electronic products is becoming more and more powerful, and its integration and assembly density continue to improve, which will lead to the increase of its working power consumption and heat. If not timely treatment of heat dissipation problems, which will lead to heat concentration in the diode PN junction, it will reduce the service life of LED lights, and in severe cases, it will even burn the LED device. Therefore, it is crucial to improve heat dissipation efficiency of LED and reduce the junction temperature of chip. An LED structure with aluminum material and an LED structure with graphene material are analyzed by finite element method to study the heat dissipation efficiency of the graphene material. The results reveal that the heat dissipation effect of high conductivity graphene composites provides a convenient evaluation method for the subsequent use of the new materials. The research in this paper shows that the software simulation method can effectively analyze the thermal conductivity of practical engineering applications.

Dispersion and bandgap feature of coupled Bloch waves in one-dimensional piezoelectric semiconductor phononic crystal with PN junction

Dispersion and bandgap feature of coupled Bloch waves in one-dimensional piezoelectric semiconductor phononic crystal with PN junction

Enhanced solar hydrogen evolution by laminated integration of n+p-SiIP/TiO2/Pt inverted pyramid black Si photocathode

The nano/microstructuring of silicon (Si) via chemical methods has garnered significant attention due to its excellent light-trapping capabilities across a wide spectral range. Current research has predominantly focused on the synthesis of pyramidal-shaped microtextures, which enable two reflections on the surface, while largely overlooking the superior light-trapping potential of inverted pyramid silicon (SiIP) microtextures, which theoretically allow for three reflections. Moreover, there has been limited investigation into the application of inverted pyramid black silicon for solar-driven hydrogen evolution. This study reports the synthesis of uniformly arranged inverted pyramid-textured black silicon using the copper-assisted chemical etching (Cu-ACE) method to enhance the efficiency of solar-driven water splitting for hydrogen production. The formation mechanism and the influence of copper-localized surface plasmon resonance (Cu-LSPR) from Cu nanoparticle (NP) byproducts on photoelectrochemical (PEC) activity were systematically analyzed. To reduce sidewall defects and minimize photogenerated carrier recombination, the surface of the SiIP was treated with tetramethylammonium hydroxide (TMAH). A vertical PN junction was developed through ion implantation to reduce the external bias of the SiIP. Additionally, a uniform TiO₂ antireflective layer was deposited via atomic layer deposition (ALD), reducing the average reflectance of the SiIP-T4 to 5.78 % over the 300–1100 nm wavelength range. MoSₓ and Pt NPs were electrodeposited to improve the fill factor and enhance HER kinetics. With optimized catalyst loading, the n+p-SiIP-T4/TiO₂/Pt 80 mC electrode achieved a photocurrent density of 8.0 mA cm−2 at 0 V vs. RHE, an applied bias photon-to-current efficiency (ABPE) of 0.93 % at 0.24 V vs. RHE, and a double-layer capacitance (Cdl) of 91 μF cm−2. The onset potential (Von) was positively shifted by ∼1.13 V to 0.49 V vs. RHE compared to a SiIP photocathode, and the photocathode operated continuously at 0 V vs. RHE for 27 h in an acidic electrolyte. These results demonstrate that SiIP has significant potential for PEC hydrogen evolution, with further performance optimization achievable through structural and surface engineering.

Mechanism of Defect Passivation in Sb2Se3 Solar Cells via Buried Selenium Seed Layer

AbstractQuasi‐1D antimony selenide (Sb2Se3) is known for its stable phase structure and excellent light absorption coefficient, making it a promising material for high‐efficiency light harvesting. However, the (Sb4Se6)n ribbons align horizontally, increasing defect interference and limiting vertical carrier transport. Herein, a novel strategy of burying selenium (Se) seed layers to reduce lattice mismatch at the heterojunction interface, promote crystal orientation, mitigate deep donor defects, increase P‐type carrier concentration, and purify the PN junction, is proposed. Admittance spectroscopy reveals that Sb2Se3 solar cells with Se seed layers have higher activation energies for defect states and significantly lower defect densities (1.2 × 1014, 2.7 × 1014, and 1.3 × 1015 cm−3 for D1, D2, and D3) compared to an order of magnitude higher densities in Sb2Se3 solar cells without a Se seed layer. First‐principles calculations support these findings, showing that Se seed layers create a Se‐rich environment, reducing selenium vacancies (VSe), antimony on selenium sites (SbSe), and interface defects. This dual passivation mechanism suppresses defect formation and activation, increasing carrier concentration and open‐circuit voltage (VOC). Ultimately, employing this novel method, a VOC of 498.3 mV and an efficiency of 8.42%, the highest performance reported for Sb2Se3 solar cells prepared via vapor transport deposition (VTD), are achieved.

Band alignments, conduction band edges and intralayer bandgap renormalisation in MoSe2/WSe2 heterobilayers

Abstract Stacking two semiconducting transition metal dichalcogenide (MX2) monolayers to form a heterobilayer creates a new variety of semiconductor junction with unique optoelectronic features, such as hosting long-lived dipolar interlayer excitons. Despite many optical, transport, and theoretical studies, there have been few direct electronic structure measurements of these junctions. Here, we apply angle-resolved photoemission spectroscopy with micron-scale spatial resolution (µARPES) to determine the band alignments in MoSe2/WSe2 heterobilayers, using in-situ electrostatic gating to electron-dope and thus probe the conduction band edges. By comparing spectra from heterobilayers with opposite stacking orders, that is, with either MoSe2 or WSe2 on top, we confirm that the band alignment is type II, with the valence band maximum in the WSe2 and the conduction band minimum in the MoSe2. The overall band gap is EG = 1.43 ± 0.03 eV, and to within experimental uncertainty it is unaffected by electron doping. However, the offset between the WSe2 and MoSe2 valence bands clearly decreases with increasing electron doping, implying band renormalisation only in the MoSe2, the layer in which the electrons accumulate. In contrast, µARPES spectra from a WS2/MoSe2 heterobilayer indicate type I band alignment, with both band edges in the MoSe2. These insights into the doping-dependent band alignments and gaps of MX2 heterobilayers will be useful for properly understanding and ultimately utilizing their optoelectronic properties.

Scaling Behavior in the Spectral and Power Density Dependent Photovoltaic Response of Hot Polaronic Heterojunctions

AbstractStrongly correlated manganites can be considered as model systems for the study of photovoltaic harvesting of hot polarons that can be excited from the electronically ordered ground state. In order to gain basic understanding of hot polaron harvesting, the deviations of the photovoltaic response of a heterojunction with polaronic absorber from a conventional semiconductor are analyzed. Specifically, the spectral and photon power density dependence of the open circuit voltage Uoc and the short circuit current density Jsc in heterojunctions consisting of orbital ordered Pr1‐xCaxMnO3 (x = 0.1, PCMO) thin films epitaxially grown on single crystalline (100) SrTiO3 (STO) and Nb‐doped (100) SrTiO3 (STNO) substrates are investigated. The observed behavior is fundamentally different from conventional solar cells, in which Uoc is limited by fast carrier relaxation to the band edges. Whereas the spectral and photon power dependence of Uoc of conventional semiconductor junctions is well described by the Shockley‐Queisser (SQ) theory, the hot polaron junctions surprisingly show a scaling law behavior of Uoc. Such scaling laws otherwise apply to equilibrium order parameters in second‐order phase transitions. It is concluded that its physical origin is the unique dependence of the quasi‐Fermi level splitting on temperature, photon energy, and power density in a hot polaron system.

Perovskite Co-doping LaNiO3 quantum dots modified NiO/BaTiO3 transparent pn junction towards photovoltaic enhancement via bimetallic synergism

Transparent device in perovskite Co-LaNiO3 QDs modified NiO/BaTiO3 is prepared via an approach of sol-gel-annealing-chemical deposition method. The obtained NiO/Co-LaNiO3 QDs/BaTiO3 (NiO/BTO-LaCoNi-2) exhibits high transmittance of ∼80–85 %, obvious photovoltaic enhancement of ∼2.01 × 103-folds (PCE of ∼1.12 %) than NiO/BTO, stable output in ∼28000s. It can be mainly attributed to the perovskite Co-LaNiO3 QDs modification. Besides appropriate Fermi level and high quantum yield (DFT supporting), the Co-LaNiO3 QDs with extra carrier injecting/driving from synergism of charge compensation, bimetallic synergism and lattice distortion can improve the carrier kinetic equilibrium for PCE-transparency balance, meanwhile increasing the p-type conductivity via Cu vacancy/Ni vacancy/interstitial oxygen synergism. Moreover, the surface orderly nanosheets arrays can increase solar efficiency, while inorganic NiO, Co-LaNiO3 QDs, BaTiO3 and orderly interval with structural stability are beneficial for the actual applications.

Modeling the diffusion and depletion capacitances of a silicon pn diode in forward bias with impedance spectroscopy

We investigated the capacitance of a forward-biased silicon pn diode using impedance spectroscopy. Despite extensive research spanning decades, no single model in the literature adequately describes the impedance behavior for bias up to the built-in voltage. By employing the 1N4007 diode as a case study, we analyzed the impedance over a wide frequency range, from 1 Hz to 1 MHz. Our analysis reveals that impedance can be effectively studied by combining two models. In both models, the depletion capacitance is assumed to be an ideal capacitor with a value independent of frequency. One model accounts for diffusion processes, while the other addresses interfacial effects, as well as potential and capacitance distributions across the junction. This approach offers valuable insights into the complex capacitance behavior of pn junctions as a function of the bias voltage. Measurements of depletion and diffusion capacitances, as well as of the diode transit time can be achieved from a set of impedance spectroscopy data.

Easy-to-configure zero-dimensional valley-chiral modes in a graphene point junction.

The valley degree of freedom in two-dimensional (2D) materials can be manipulated for low-dissipation quantum electronics called valleytronics. At the boundary between two regions of bilayer graphene with different atomic or electrostatic configuration, valley-polarized current has been realized. However, the demanding fabrication and operation requirements limit device reproducibility and scalability toward more advanced valleytronics circuits. We demonstrate a device architecture of a point junction where a valley-chiral 0D PN junction is easily configured, switchable, and capable of carrying valley current with an estimated polarization of ~80%. This work provides a building block in manipulating valley quantum numbers and scalable valleytronics.

Power Semiconductor Junction Temperature and Lifetime Estimations: A Review

The lifetime of power electronic systems is the focus of both the academic and industrial worlds. Today, compact systems present high switching frequency and power dissipation density, causing high junction temperatures and strong thermal fluctuations that affect their performance and lifetime. This paper is a review of the existing techniques for the electro-thermal modelling of Mosfet and IGBT devices regarding lifetime estimation. The advantages and disadvantages of the methodologies used to achieve lifetime prediction are discussed, and their benefits are highlighted. All the factors required to predict power electronic device lifetime, including Mosfet and IGBT electrical models, the computation of power losses, thermal models, temperature measurement and management, lifetime models, mission profiles, cycle counting, and damage accumulation, are described and compared.

Self-cleaning transparent Cu2Y2O5/Tb:Bi2Sn2O7 quantum dots/Bi2O3 pn junction for photovoltaic enhancement via synergism of up-conversion fluorescence and surface hydrophobicity

The competitiveness between photovoltaic conversion efficiency (PCE) and transparency would be the bottleneck of transparent device for actual applications, as well as the high maintenance cost. In this work, the self-cleaning transparent device in interfacial Tb:Bi2Sn2O7 QDs modified Cu2Y2O5/Bi2O3 pn junction is prepared via a simple approach of sol-gel-hydrothermal method. The obtained Cu2Y2O5/Tb:Bi2Sn2O7 QDs/Bi2O3 exhibits high transmittance of ∼85 %, obvious photovoltaic enhancement of ∼2.0 × 103-folds (PCE of ∼1.17 %), stable output in 5 months cycles and a good self-cleaning via the hydrophobicity (contact angle of ∼123.4°). It's mainly attributed to the Tb:Bi2Sn2O7 QDs and lamellar Bi2O3 array. Besides appropriate potential and high quantum yield, the Tb:Bi2Sn2O7 QDs, with the synergism of up-conversion fluorescence and interface/surface optimization, can improve the carrier kinetic equilibrium for achieving PCE-transparency balance, as well as increasing p-type conductivity through the synergism of Cu+/Cu2+ and interstitial oxygen. Moreover, the regular lamellar array can enhance solar efficiency via optimized surface, meanwhile achieving self-cleaning via the surface hydrophobicity and enhancing structural stability via the regular interval, making it being advantageous in actual applications of energy and information field, including windows, smart devices, etc.

General Theory for Longitudinal Nonreciprocal Charge Transport.

The longitudinal nonreciprocal charge transport (NCT) in crystalline materials is a highly nontrivial phenomenon, motivating the design of next generation two-terminal rectification devices (e.g., semiconductor diodes beyond PN junctions). The practical application of such devices is built upon crystalline materials whose longitudinal NCT occurs at room temperature and under low magnetic field. However, materials of this type are rather rare and elusive, and theory guiding the discovery of these materials is lacking. Here, we develop such a theory within the framework of semiclassical Boltzmann transport theory. By symmetry analysis, we classify the complete 122magnetic point groups with respect to the longitudinal NCT phenomenon. The symmetry-adapted Hamiltonian analysis further uncovers a previously overlooked mechanism for this phenomenon. Our theory guides the first-principles prediction of longitudinal NCT in multiferroic ϵ-Fe_{2}O_{3} semiconductor that possibly occurs at room temperature, without the application of external magnetic field. These findings advance our fundamental understandings of longitudinal NCT in crystalline materials, and aid the corresponding materials discoveries.

Strongly Coupled NiMo@Alloy‐LDH Interfaces with Low‐Barrier Schottky Junctions for Oxygen Evolution Reaction

AbstractThe main challenge in developing Schottky‐contact OER catalytic devices based on layered double hydroxides (LDHs) is to achieve metal–semiconductor junctions with low contact resistance and high charge transfer capacity. However, due to the presence of high potential barriers and Fermi pinning, conventional Schottky contacts are usually unsatisfactory, resulting in poor‐working electrode performance and high energy consumption. In this study, a new concept of “hindrance factor” is introduced to quantify the difficulty of electron transfer, and a low‐hindrance factor Schottky contact formed by strong coupling of semiconductor LDH and NiMo alloy clusters is designed. This interface guides charge redistribution, optimizes the bonding and orbital states of adsorption sites, and enhances the targeted adsorption of OH intermediates. The results show that the configured NiMo@NiFeCe‐LDH working electrode only needs 1.445 V (vs RHE) to drive the reaction and shows excellent durability in 400 h of testing. At the same time, based on this study, a strategy for screening high‐performance Schottky junctions is developed. This strategy provides a bridge for studying interface properties, orbital hybridization, and charge transfer, reveals the potential mechanism for reducing contact resistance, and has important guiding significance for screening high‐performance metal–semiconductor electrocatalysts and stability.

Self-cleaning transparent photovoltaic device in perovskite SrTiO3 quantum dot modified CuGaO2/Zn2SnO4 nanoarrays pn junction via surface plasma modification

A self-cleaning transparent pn junction in perovskite SrTiO3 QDs modified CuGaO2/Zn2SnO4 nanoarrays is prepared via the hydrothermal-solgel-surface plasma (SP) method. The CuGaO2/SrTiO3 QDs/Zn2SnO4 exhibits transmittance of ∼85%–90%, photovoltaic enhancement of ∼1.8 × 103-folds (photovoltaic conversion efficiency of ∼1.25%), stable output in 5 months, and good hydrophobicity (contact angle of ∼138.1°). The main reasons are mainly attributed to the SrTiO3 QDs and SP modification; besides the appropriate Fermi level and high quantum yield can improve the carrier kinetic equilibrium for balancing transparency-photovoltaic conversion efficiency, the SP modification can enhance the solar and carrier efficiency further, meanwhile achieving self-cleaning. Additionally, the CuGaO2 orderly nanoarrays can release stress, increase solar efficiency, and promote carrier transportation, in order to balance the structural stability, transparency, and photovoltaic efficiency.