Metal-semiconductor Contact Research Articles

Construction of efficient silicon solar cells through polymetallic oxidation-reduction triggered by thermite reaction

Optimal metal-semiconductor contact interface is crucial for semiconductor devices, particularly for silicon solar cells aluminum-silicon contact is a key to improve the efficiency of the cell. In this work, a new type of Sb2O3-MoO3-B2O3 glass frits that can trigger a thermite reaction was utilized to improve the Al-Si interface. The low melting temperatures of these glass frits enhance the effect of thermite reaction by providing solid-liquid contact, which enables gradient distribution of the elements and leads to differences in the valence states of the Al-Si layer at the inner and surface regions. The valence states of Al and Sb at the inner layer are higher than those at the surface, while Mo is the opposite. Metallic Mo with a matched work function can lower the potential barrier, thereby improving hole selectivity and enhancing the potential skip-step. As a result, the fabricated solar cell achieved a high open-circuit voltage, a high short-circuit current, and a low series resistance. Consequently, a power conversion efficiency of 19.94% was obtained for a monocrystalline silicon solar cell with full Al-BSF. This work not only presents a new hole-selective contact for silicon solar cells, but also introduces a new approach for regulating the distribution and valence states of interface elements for enhanced efficiency.

A new line tunneling SiGe/Si iTFET with control gate for leakage suppression and subthreshold swing improvement

This article presents a new line tunneling dominating metal–semiconductor contact-induced SiGe–Si tunnel field-effect transistor with control gate (CG-Line SiGe/Si iTFET). With a structure where two symmetrical control gates at the drain region are given a sufficient negative bias, the overlap of the energy bands at the drain in the OFF-state is effectively suppressed, thus reducing the tunneling probability and significantly decreasing leakage current. Additionally, the large overlap area between the source and gate improves the gate’s ability to control the tunneling interface effectively, improving the ON-state current and subthreshold swing characteristics. By using the Schottky contact characteristics of a metal–semiconductor contact with different work functions to form a PN junction, the need to control doping profiles or random doping fluctuations is avoided. Furthermore, as ion implantation is not required, issues related to subsequent annealing are also eliminated, greatly reducing thermal budget. Due to the different material bandgap characteristics selected for the source and drain regions, the probability of overlap of the energy bands in the source region in the ON-state is increased and that in the drain region in the OFF-state is reduced. Based on the feasibility of the actual fabrication process and through rigorous 2D simulation studies, improvements in subthreshold swing and high on/off current ratio can be achieved simultaneously based on the proposed device structure. Additionally, the presence of the control gate structure effectively suppresses leakage current, further enhancing its potential for low-power-consumption applications.

Oxygen-Induced Barrier Lowering for High-Performance Organic Field-Effect Transistors.

Organic field-effect transistors (OFETs) have the advantages of low-cost, large-area processing and could be utilized in a variety of emerging applications. However, the generally large contact resistance (Rc) limits the integration and miniaturization of OFETs. The Rc is difficult to reduce due to an incompatibility between obtaining strong orbit coupling and the barrier height reduction. In this study, we developed an oxygen-induced barrier lowering strategy by introducing oxygen (O2) into the nanointerface between the electrodes and organic semiconductors layer and achieved an ultralow channel width-normalized Rc (Rc·W) of 89.8 Ω·cm and a high mobility of 11.32 cm2 V-1 s-1. This work demonstrates that O2 adsorbed at the nanointerface of metal-semiconductor contact can significantly reduce the Rc from both experiments and theoretical simulations and provides guidance for the construction of high-performance OFETs, which is conducive to the integration and miniaturization of OFETs.

Two-dimensional MoS2/Ti2CX2 (X = S, Se, Te) heterostructures with tunable electrical contact type

The tunable electrical contact type in van der Waals (vdW) heterostructures plays an important role in promoting the efficiency of ultrathin electronic devices. From the first-principles calculations, the electronic properties and electrical contact type of the MoS2/Ti2C heterostructure and its ramifications MoS2/Ti2CX2 (X = S, Se, Te) heterostructures are verified. The strong interfacial interaction is found in pristine MoS2/Ti2C heterostructure, resulting in the metallization of MoS2 layer. The functionalization of S, Se, and Te atoms can weaken the interfacial interaction, forming metal-semiconductor contact. The p-type Schottky contact is formed in MoS2/Ti2CS2 and MoS2/Ti2CSe2 heterostructures, while Ohmic contact is formed in MoS2/Ti2CTe2 heterostructure. The application of external electric field can efficiently modulate the contact type of MoS2/Ti2CX2 (X = Se and Te) heterostructures. The discrepancy of electron affinity of S, Se, and Te atoms leads to the different interlayer charge transfer, and thus the different electrical contact type can be realized in MoS2/Ti2CX2 (X = S, Se, Te) heterostructures. The tunable contact type makes these heterostructures become potential candidate materials for enhancing the nanoelectronic devices’ efficiency.

Optimizing Hot Electron Harvesting at Planar Metal-Semiconductor Interfaces with Titanium Oxynitride Thin Films.

Understanding metal-semiconductor interfaces is critical to the advancement of photocatalysis and sub-bandgap solar energy harvesting where electrons in the metal can be excited by sub-bandgap photons and extracted into the semiconductor. In this work, we compare the electron extraction efficiency across Au/TiO2 and titanium oxynitride (TiON)/TiO2-x interfaces, where in the latter case the spontaneously forming oxide layer (TiO2-x) creates a metal-semiconductor contact. Time-resolved pump-probe spectroscopy is used to study the electron recombination rates in both cases. Unlike the nanosecond recombination lifetimes in Au/TiO2, we find a bottleneck in the electron relaxation in the TiON system, which we explain using a trap-mediated recombination model. Using this model, we investigate the tunability of the relaxation dynamics with oxygen content in the parent film. The optimized film (TiO0.5N0.5) exhibits the highest carrier extraction efficiency (NFC ≈ 2.8 × 1019 m-3), slowest trapping, and an appreciable hot electron population reaching the surface oxide (NHE ≈ 1.6 × 1018 m-3). Our results demonstrate the productive role oxygen can play in enhancing electron harvesting and prolonging electron lifetimes, providing an optimized metal-semiconductor interface using only the native oxide of titanium oxynitride.

Determination of temperature sensitivity and current-transport mechanisms of the GaAs-based MS contact

In this study, the GaAs-based metal-semiconductor (MS) contact was prepared as a reference sample for comparison with other devices in the literature, especially some interfacial layered Schottky structures and temperature sensors. The study also includes investigating and evaluating essential device parameters for determining current-transport mechanisms (CTMs) and temperature-sensing behavior. In fact, the benefits of the insulator/organic interfacial layer in devices, such as controlling charge transfers and preventing diffusion at the MS interface, have been mentioned a lot in the literature. However, since the production processes of the MS contact are easier and less costly than interfacial-layered devices, it would be more logical/suitable to prefer it in applications where this device may be sufficient, especially as a temperature sensor. Therefore, the current-voltage (I-V) data of the produced MS contact was obtained in a wide temperature range to determine the CTMs, and it was observed that two linear areas with different slopes, known as the two-parallel diode model, existed in the GaAs-based MS contact. Therefore, essential contact parameters and graphs were obtained for both two regions, and it was obtained that quantum mechanical tunneling mechanisms, the T0 effect, and the Double Gaussian Distribution (DGD) with Thermionic Emission theory play a role as CTMs of the GaAs-based MS contact such as some interfacial layered devices given in the literature. On the other hand, the temperature sensitivity of the MS contact was examined, and it was observed that the sensitivity parameter values exhibit an excellent quality sensing behavior compared to other devices in the literature, including devices with high-temperature sensitivity. Therefore, it can be preferred as a temperature sensor in many applications due to its low cost and easy production processes.

Ionic accelerator based on metal–semiconductor contact for fast electrode kinetics and durable Zn-metal anode

The development of Zn metal anodes with high reversibility and fast kinetics is critical for achieving high-performance aqueous Zn-metal batteries. Herein, we report a Zn@SiC electrode with an Ohmic contact that exhibits excellent durability and enhanced electrode process kinetics. The Ohmic contact barrier (Φb) inhibited electron transfer from the metal to the SiC passivation layer and effectively regulated Zn deposition under the passivation layer, thus suppressing dendrite growth. The built-in potential (Vbi) accelerated the Zn transfer and reaction kinetics and decreased the nucleation energy, thereby enhancing the charge–discharge platform potential (∼40 mV) in full cells. Coupled with the good anti-side reaction ability of the SiC layer, the Zn@SiC electrode successfully delivered a highly reversible stripping/plating process after 3770 h under a 1.0 mA cm−2 current density with a low overpotential of 33.7 mV. Furthermore, by analyzing the energy band structure of the Ohmic contacts, the critical current density was quantitatively determined. This clarified the relationship between the deposition position and the current density, thus providing a standard for practical semiconductor design.

Interfacial characteristics, metal-semiconductor contact and optical properties of CSe and BX (X=B, As and Sb) monolayers

Two dimensional (2D) materials with large family recently drawn tremendous attention due to their versatile applications. Appreciating the smooth surface and atomic thickness of 2D materials, which can be constructed in the form of heterostructures, resulting interesting chemical and physical properties in many fields. Particularly, 2D metal-semiconductor contact (MS contact), shown great promise in nanodevices and optoelectronic devices application. In this work, we have constructed the MS contact of CSe and BX (X = P, As and Sb) monolayers and investigated the interfacial characteristics, Schottky contact and optical properties, using density functional theory. Our calculated binding energies and thermal stability confirm that CSe-BX (X = P, As and Sb) MS contact are dynamically and thermally stable. Our prediction shows that CSe-BX (X = P, As and Sb) MS contact forms n-type contact, while well preserved the properties of both monolayers. A small band gap opening in CSe having high carrier mobilities, indicated that CSe-BX (X = P, As and Sb) MS contact are good candidates for high speed nanoelectronics applications. Electrostatic potential and Bader charge analysis confirm that electrons are transfer from CSe layer to the BS monolayers and the potential drops separates charge carrier at the interface, play crucial rule in power conversion efficiency. The imaginary part shows an intense absorption peak near the visible region, hence shows appalling application in photoelectronic and optical transmissions.

X-ray and electrical characterization of a multipixel diamond-based detector in high temperature environments

An 8-pixel X-ray diamond detector prototype, fabricated on an alumina substrate and specifically designed to operate at high temperature, has been developed and tested. Tungsten electrodes were developed as metal-semiconductor contact and showed an ohmic behavior, as inferred from current-voltage measurements. A 40-cycles thermal stress test performed in helium atmosphere, in which temperature has been varied cyclically between 100 and 240 °C, showed minor evolution of the detector dark current, presumably related to progressive water desorption from the alumina substrate. Conversely, X-ray photocurrent measurements showed no significant differences before and after the thermal cycles, confirming no degradation of the stability of the prototype even after prolonged operation at high temperature.

Achieving Ultrahigh Electron Mobility in PdSe2 Field‐Effect Transistors via Semimetal Antimony as Contacts

AbstractEven though atomically thin 2D semiconductors have shown great potential for next‐generation electronics, the low carrier mobility caused by poor metal–semiconductor contacts and the inherently high density of impurity scatterings remains a critical issue. Herein, high‐mobility field‐effect transistors (FETs) by introducing few‐layer PdSe2 flakes as channels is achieved, via directly depositing semimetal antimony (Sb) as drain–source electrodes. The formation of clean and defect‐free van der Waals (vdW) stackings at the Sb–PdSe2 heterointerfaces boosts the room temperature transport characteristics, including low contact resistance down to 0.55 kΩ µm, high on‐current density reaching 96 µA µm−1, and high electron mobility of 383 cm2 V−1 s−1. Furthermore, metal–insulator transition (MIT) is observed in the PdSe2 FETs with and without hexagonal boron nitride (h–BN) as buffer layers. However, the layered h–BN/PdSe2 vdW stacking eliminates the interference of interfacial disorders, and thus the corresponding device exhibits a lower MIT crossing point, larger mobility exponent of γ ∼ 1.73, significantly decreased hopping parameter of T0, and ultrahigh electron mobility of 2,184 cm2 V−1 s−1 at 10 K. These findings are expected to be significant for developing high mobility 2D‐based quantum devices.

The Comparison of the Temperature Susceptibility of the Serial Resistance Effect of Au/n-GaAs Type M/S Structures

To enable comparison with the literature, this study seeks to assess the temperature susceptibility of serial resistance (Rs) features of the Au/n-GaAs type M/S structure, which is acceptable the benchmark sample. The serial resistance features of the sample were computed separately withal principal of Ohm, Norde, and Cheungs' functions. The current-voltage (I-V) data used in order to compute were evaluated at the voltage values between +2V and -2 V and temperature values between 120K and 360K in 60K steps. Each computation method was also compared one another other. As a result, the fact that the Rs values computed using principal of Ohm, Norde functions and Cheungs' functions tended to reduce with rising temperature, as anticipated by the literature results. In addition, it was determined that, with only tiny variations, the temperature susceptibility of Rs is consistent across all computation methods. In addition, as a result of the comparison with the literature, it was concluded serial resistance is less of an issue when a polymer interfacial layer is present at the metal-semiconductor contact region. The Rs parameter of the M/S structure is, in essence, a sensitive function of temperature and input voltage.

Investigation of 1/f noise sources with the coherence function

We demonstrate the application of the coherence function to analyze the 1/f noise sources in a planar semiconductor structure with multiple electrical contacts. This article includes noise and coherence function measurements, the 1/f noise model for the transmission-line-model (TLM) sample, theoretical calculations of the coherence function, and a comparison of theoretical and experimental values. In the developed noise model, bulk semiconductor noise and metal–semiconductor contact noise are considered noise sources. It was shown that the experimental results of coherence measurements are well explained by the model, which assumes 1/f noise from contacts and no 1/f noise from a bulk semiconductor. The presented method can be used to find dominant noise sources originating from bulk semiconductor or metal–semiconductor contacts in planar structures. The strength of the method, in comparison with models based only on power spectral density, is straightforward interpretation and the lack of sophisticated model parameters.

Fast near-infrared photodetectors from p-type SnSe nanoribbons

Low-dimensional tin selenide nanoribbons (SnSe NRs) show a wide range of applications in optoelectronics fields such as optical switches, photodetectors, and photovoltaic devices due to the suitable band gap, strong light–matter interaction, and high carrier mobility. However, it is still challenging to grow high-quality SnSe NRs for high-performance photodetectors so far. In this work, we successfully synthesized high-quality p-type SnSe NRs by chemical vapor deposition and then fabricated near-infrared photodetectors. The SnSe NR photodetectors show a high responsivity of 376.71 A W−1, external quantum efficiency of 5.65 × 104%, and detectivity of 8.66 × 1011 Jones. In addition, the devices show a fast response time with rise and fall time of up to 43 μs and 57 μs, respectively. Furthermore, the spatially resolved scanning photocurrent mapping shows very strong photocurrent at the metal-semiconductor contact regions, as well as fast generation-recombination photocurrent signals. This work demonstrated that p-type SnSe NRs are promising material candidates for broad-spectrum and fast-response optoelectronic devices.

Light–induced transition of charged carrier transport in symmetric metal–semiconductor–metal contacts

Metal–semiconductor (M–S) contact is a basic element in semiconductor integrated circuit. Recent studies on photodetectors extensively focus on M–S contact owing to the easy fabrication and superior performance. Here, we report a light–induced transition of charged carrier transport in planar Cu/Si–doped GaAs single crystal (Si:GaAs) symmetric double Schottky contacts. Different from conventional photodetector, illumination not only gains the carrier concentration but also changes the charged carrier transport mechanism at Cu/Si:GaAs contact. The light-induced transition of charged carrier transport is reflected by the change of shape of current–voltage (I–V) curve caused by illumination. By the construction of theoretical model and its fitting to experimental data, we point out that carrier transport mechanism at Cu/Si:GaAs contact changes from tunneling effect to thermionic emission by illumination. Among that, photovoltaic effect is the crucial driving force. This study presents a novel mechanism for converting optical signal to electrical signal by tailoring Schottky contact in photodetector, which provide a design prototype to new–type optoelectronic device.

Low resistance electrical contacts to few-layered MoS2 by local pressurization

The performance of electronic and optoelectronic devices is dominated by charge carrier injection through the metal–semiconductor contacts. Therefore, creating low-resistance electrical contacts is one of the most critical challenges in the development of devices based on new materials, particularly in the case of two-dimensional semiconductors. Herein, we report a strategy to reduce the contact resistance of MoS2 via local pressurization. We fabricated electrical contacts using an atomic force microscopy tip and applied variable pressure ranging from 0 to 25 GPa. By measuring the transverse electronic transport properties, we show that MoS2 undergoes a reversible semiconducting-metallic transition under pressure. Planar devices in field effect configuration with electrical contacts performed at pressures above ∼15 GPa show up to 30-fold reduced contact resistance and up to 25-fold improved field-effect mobility when compared to those measured at low pressure. Theoretical simulations show that this enhanced performance is due to improved charge injection to the MoS2 semiconductor channel through the metallic MoS2 phase obtained by pressurization. Our results suggest a novel strategy for realizing improved contacts to MoS2 devices by local pressurization and for exploring emergent phenomena under mechano-electric modulation.

Bi-polysilicon passivating contact technique for crystalline silicon solar cell

Polysilicon (poly-Si) passivating contacts overcome the direct metal–semiconductor contact drawback of traditional industrial crystalline silicon (c-Si) solar cells by inserting a layer stack of poly-Si and silicon oxide layers at the rear full-area metal/c-Si interface, which is well-known as a tunnel oxide passivating contact (TOPCon). In conventional industrial TOPCon devices, the direct contact problem affects the emitter, which deteriorates the passivation quality and suppresses the open-circuit voltage (Voc). We herein introduce an innovative bi-poly-Si technique (Bi-TOPCon) featuring rear full-area passivated poly-Si and emitter locally passivated poly-Si to improve the passivation quality of the TOPCon device. The local emitter poly-Si is introduced using metal mask alignment, and its properties are optimised toward high passivation quality and low contact resistance. The Bi-TOPCon device shows a significant improvement in Voc (Voc > 700 mV). Bi-TOPCon is a promising technology for high-efficiency, next-generation industrial TOPCon devices.

Efficient Ohmic Contact in Monolayer CrX2N4 (X = C, Si) Based Field‐Effect Transistors (Adv. Electron. Mater. 3/2023)

Metal–Semiconductor Contacts In article number 2201056, Baisheng Sa and co-workers report the achievement of Ohmic and quasi-Ohmic contact in CrX2N4 (X = C, Si) contacts, which is due to Fermi level pinning effects. Thereby, channels are provided for electrons to pass through linked field-effect transistors easily. This system is analogous to high-speed trains going through mountain tunnels without climbing the peaks.

Promotion of dual-reaction pathway in CO2 reduction over Pt0/SrTiO3–δ: Experimental and theoretical verification

The H2 evolution is generally considered a competing reaction in photocatalytic CO2 reduction reaction (CO2RR) using H2O as the proton source. However, the reducing gas H2 generated from H2O splitting can be the proton source in CO2RR under the enhanced dynamic role of the thermal effect. The reverse water gas shift (RWGS) reaction, a CO2 hydrogenation reaction, should occur in photothermal environment owing to thermodynamically and kinetically favorable. Herein, nanostructured metal-semiconductor contact consisting of Pt nanoparticles (NPs) supported on SrTiO3–δ nanosheets with rich oxygen vacancies (Pt-OVs-STO) was constructed for investigating its feasibility and efficiency in the RWGS reaction under photothermal effect. Our experimental results substantiate that the H2 generated by H2O splitting effectively contributes to the RWGS reaction over Pt-OVs-STO system. The Pt0 NPs not only efficiently facilitate surface charge transfer, but also lower the energy barrier of the O–H bond breaking, H2 releasing, and RWGS reaction, thereby showing an outstanding CO2RR performance. The strong interaction between the Pt0 NPs and SrTiO3–δ has been extensively demonstrated by a series of experimental characterizations and density functional theory calculations. This work elucidates the relation between H2 evolution and RWGS reaction over Pt0/SrTiO3–δ structure in photothermal catalytic CO2RR using H2O as the proton source and provides new perspectives for subsequent CO2RR.

New method of measuring the permittivity of silicon wafer, with relevance to permittivity-based quality sensing

A new method of measuring the permittivity of silicon wafers is provided. It removes the previously reported dependence of the measured permittivity on the silicon resistivity and on the electrode quality. Metal-semiconductor contacts or thin-film electrodes are not required. The method innovatively uses N-segment (e.g., N = 7) sandwiching aluminum-foil electrodes adhered to both surfaces of the wafer using double-sided adhesive tape, which provides adhesion and resistance enhancement (for ensuring that the meter measures the capacitance correctly). By measuring the capacitance C for various values of the capacitor area A (as provided by different numbers of segments) and plotting 1/C vs. 1/A, the permittivity is obtained from the slope and the effect of the electrode-specimen interface capacitance is removed. The relative permittivity (12) equals the conventionally obtained values. By using a sufficiently high value of N, the permittivity spatial distribution can be probed, thus enabling spatially resolved permittivity-based quality sensing.

Influence of oxygen vacancy and metal–semiconductor contact on the device performance of amorphous gallium oxide photodetectors

Here we investigate the influence of the oxygen vacancy content and the electrode contact on the performance of deep ultraviolet photodetectors based on amorphous Ga2O3 films. The fine-tuning of the oxygen ratio effectively reduces the oxygen vacancy content, which obtains optimized device performance with a responsivity of 5.78 A W−1 and a rise/fall time of 301/89 ms. The metal contact formation and its impact on the device performance are further studied. Compared to the Ohmic-type device using Ti electrodes, the Schottky-type devices using Au and Al electrodes exhibit a shorter rise time and a lower dark current.