Current Carrier Mobility Research Articles

High-performance ultraviolet Cs3Cu2I5 photodetector derived from two-step annealing process

Perovskite based ultraviolet photodetectors have great potential in fire warning, disease treatment and missile guidance, etc. owing to its high mobility, large absorption coefficient and solution processability. However, poor stability and toxic lead element hinder it further applications in current stage. Recently, all-inorganic lead-free perovskite Cs3Cu2I5 demonstrates great potential in ultraviolet detection for its outstanding long-term stability and suitable bandgap. Nevertheless, pinholes and roughness of film lead to leakage current and lower carrier mobility, restricting detection performance. Herein, a two-step annealing method was introduced to optimize the nucleation and crystallization of Cs3Cu2I5 grains. Owing to the improvement of grain quality, fewer pinholes and precipitated phases occurred during crystallization process, thus, resulting in compact and smooth film surface. The hole and electron mobilities of the two-step annealed film were promoted up to 0.697 cm2/(V·s) and 1.579 cm2/(V·s) respectively. As a consequence, the constructed Cs3Cu2I5 photodetector exhibits high on/off ratio of 6.3 × 104, a shorter response time of 26.2 ms (τrise)/49.9 ms (τfall), external quantum efficiency of 3.04%, moderate responsivity of 8.46 mA/W and detectivity of 3 × 1013 Jones. Basing on these merits, an ultraviolet imaging was demonstrated. This work provides an effective but simple strategy to endow Cs3Cu2I5 photodetector with improved performance for further applications in the future.

Study of carrier mobility in CdTe and PbTe thin films as a function of temperature

The temperature dependency of kinetic parameters in p-PbTe and p-CdTe thin films formed on glass substrates has been investigated. The surface mobility of current carriers in PbTe films was computed as a function of temperature under the assumption of diffuse scattering of charge carriers. The mechanisms of intergranular current carrier transfer related with thermoelectronic emission are established. The role of surface scattering and intergranular boundaries in thin films of lead and cadmium tellurides is addressed.

Tensoelectric properties irradiated by the fast electrons n-Ge single crystals

Tensoelectric properties of the uniaxially deformed along the crystallographic direction [100] n-Ge single crystals, irradiated by the flows of electrons , , and , with the energy of , were investigated. Mechanisms of changes in resistivity and mobility of current carriers under the uniaxial deformation for the studied n-Ge single crystals based on the measurements of tenso-Hall effect and infrared Fourier spectroscopy were established.The presence of tensoresistance for n-Ge single crystals, irradiated by the flow of the electrons , is associated with changes under the uniaxial pressure of electron concentration in the conduction band and holes in the valence band due to a decrease of the ionization energy of the deep level of the radiation defects which belongs to the complexes , at the uniaxial deformation. A significant increase of the effective mobility of carriers current in uniaxially deformed single crystals n-Ge is primarily related to the deforming redistribution of electrons between the branch of ‘light’ holes and the level . For single crystals n-Ge irradiated by the flows of electrons , which lead to the n-p conversion of the conductivity type of germanium, significant tensoresistance is observed only at the pressures . In this case, the resistivity of n-Ge decreases both due to an increase in the concentration of holes and their mobility under the deformation. Mobility of holes does not depend on deformation for uniaxial pressures , and a slight decrease in the resistivity of the researched single crystals n-Ge is caused by an increase in their concentration. Radiation-induced tensosensitivity at the room temperature for single crystals n-Ge can be used in technologies for creating uniaxial pressure sensors based on germanium. Obtained radiation effect of a significant increase in the mobility of current carriers for the uniaxially deformed n-Ge single crystals can find its practical application in the creation of ‘germanium’ channels of n-MOSFET and p-MOSFET transistors.

All-Transfer Electrode Interface Engineering Toward Harsh-Environment-Resistant MoS2 Field-Effect Transistors.

Nanoscale electronic devices that can work in harsh environments are in high demand for wearable, automotive, and aerospace electronics. Clean and defect-free interfaces are of vital importance for building nanoscale harsh-environment-resistant devices. However, current nanoscale devices are subject to failure in these environments, especially at defective electrode-channel interfaces. Here, harsh-environment-resistant MoS2 transistors are developed by engineering electrode-channel interfaces with an all-transfer of van der Waals electrodes. The delivered defect-free, graphene-buffered electrodes keep the electrode-channel interfaces intact and robust. As a result, the as-fabricated MoS2 devices have reduced Schottky barrier heights, leading to a very large on-state current and high carrier mobility. More importantly, the defect-free, hydrophobic graphene buffer layer prevents metal diffusion from the electrodes to MoS2 and the intercalation of water molecules at the electrode-MoS2 interfaces. This enables high resistances of MoS2 devices with all-transfer electrodes to various harsh environments, including humid, oxidizing, and high-temperature environments, surpassing the devices with other kinds of electrodes. The work deepens the understanding of the roles of electrode-channel interfaces in nanoscale devices and provides a promising interface engineering strategy to build nanoscale harsh-environment-resistant devices.

Gettering of epitaxial indium arsenide by the rare earth element holmium

The results of a study of the galvanomagnetic properties of indium arsenide grown by liquid-phase epitaxy are presented. It is shown that the use of the rare earth element holmium in the growth of InAs epitaxial layers makes it possible to reduce the electron concentration by two orders of magnitude to n=2.1·1015 cm-3 at T=77 K. This effect is due to the gettering of shallow background impurities with the formation of their compounds in the melt. With an increase in the holmium content of more than 0.12 mol.% the concentration of current carriers in the material begins to increase, while mobility decreases due to the influence of VAs-Ho donor centers. This method of gettering is promising for obtaining A3B5 materials with a low concentration of current carriers, which are in demand in the optoelectronic industry. Keywords: indium arsenide, rare earth element, Hall coefficient, concentration of current carriers, mobility of current carriers.

Electrophysical Properties of Monocrystalline n-Si+0.4at%Ge:P Alloy irradiated by 60Co Gamma Photons

In the monocrystal n-Si+0.4at.%Ge:P alloy irradiated with 60Co gamma photons non-monotonic changes in electrical resistance, current carrier concentration and mobility were detected by isochronal annealing at a temperature range of 20-400°C. The contribution of current transformations in the structure of radiation defects (PV, VO, VO2, CiCs, CiOi) to the temperature changes of electrical characteristics is analyzed. n-p conversion was detected at the critical temperature (~100°C) of isochronal annealing. Dissociation of PV centers and formation of electrically active VO centers were detected in the 120-150°C range. As a result, the concentration of current carriers increases. At elevated temperatures (> 150°C) non-monotonic changes in electrical characteristics are observed.The paper analyzes the contribution of Ge to the anomalous temperature changes of the electrophysical characteristics of the n-SiGe alloy.

FEATURES OF THE ELECTRICAL PROPERTIES OF HETEROJUNCTIONS N-GAAS-P-(GAAS)1 - X - У(GE2)X(ZNSE)Y

The optimal technological conditions for growing multicomponent epitaxial films of solid solutions (GaAs)1 - x - y(Ge2)x(ZnSe)y with specified physical properties by liquid-phase epitaxy have been determined. It has been established that the above conditions for growing thin films from a tin solution-melt at temperature intervals of 730-630, 650-550 °С with a substrate cooling rate of 1 deg/min are the most optimal. In this case, the films had a thickness of 10 μm and p-type conductivity. For ohmic contacts to such semiconductor solid solutions, Sn, Au, In, (In-Ga) and (Ge-Ag) alloys were used. It was determined that the mobility of current carriers depends on the composition, the structural perfection of the epitaxial layers and the ionization energy of the atoms of the constituent components have values of 0.19, 0.07, 0.029 eV. It has been established that in heterostructures of the n-GaAs-p-(GaAs)1 - x - y(Ge2)x(ZnSe)y type, obtained at Т = 7500 °С, the current transmission is determined by tunneling-recombination, and in the samples obtained at Т = 7300 °С, by currents limited volume charges. It was also determined that a region with a higher resistivity is formed at the heterointerface, the thickness of which, depending on the growth conditions of thin films, is from 0.2 to 0.5 μm.

Single layer aligned semiconducting single-walled carbon nanotube array with high linear density

Highly ordered semiconducting single-walled carbon nanotubes(sc-SWCNTs) array with high purity, high linear density and controllable manner is strongly desired for carbon-based integrated circuits, yet it remains a big challenge. Herein, close-packed single layered and controllably aligned sc-SWCNTs arrays were obtained through dielectrophoresis using a high purity sc-SWCNT dispersion. Under optimized condition of length and average number of interconnecting junctions across the channel full of aligned sc-SWCNTs, field effect transistors (FETs) with high performance were achieved with both a high on/off current ratio and large carrier mobility. Based on the optimized channel length, by systematically optimizing the dielectrophoresis parameters of the frequency and duration of applied AC voltage (V pp), the highly ordered sc-SWCNTs arrays with an ultra-high linear density of 54 ± 2 tubes μm−1 showed relatively high device performance of FET. The fabrication process optimized in this report can be further extended and applied in large-area, low-cost carbon-based integrated circuits.

Effect of heat treatment on the galvanomagnetic properties of bulk nanostructured samples of Bi85Sb15 solid solution

Extruded bulk nanostructured samples of Bi85Sb15 solid solution from particles with average sizes ∼ 2.105; 950; 650; 380; 30 and 15 nm were obtained and investigated their galvanomagnetic properties in the range of ∼ 77-300 K. Were investigated samples that have not passed heat treatment, and the same samples that have passed heat treatment. It was found that the electrical and thermal properties of Bi85Sb15 solid solution samples significantly depend on the size of nanoparticles and post-extrusion heat treatment. Heat treatment leads to a decrease in the concentration of current carriers and to an increase in the mobility of current carriers and the total thermal conductivity of the samples under study, which is mainly due to the electronic component of thermal conductivity. The change in thermal parameters is satisfactorily explained by changes in occurring in the structure of samples during extrusion and heat treatment and correlates well with changes in the electrical parameters of these processes.

The growth of large-sized graphene domains by Faraday cage-assisted plasma enhanced chemical vapor deposition

Plasma enhanced chemical vapor deposition (PECVD) is considered one of the methods to synthesize graphene with the greatest development potential due to its advantages to operate in low temperatures with high efficiency. However, unlike thermal chemical vapor deposition (TCVD), graphene grown by PECVD usually has smaller grain size with higher nucleation density of graphene films, in which excessive grain boundaries would lead to unsatisfactory electric performance for practical applications. One of the challenges in preparing graphene by PECVD is to improve the quality of graphene by controlling the nucleation and growth of graphene. In this article, the optimal growth of graphene in a Faraday cage by PECVD was studied. The nucleation density and growth rate of graphene in PECVD were decreased significantly with a Faraday cage. Large-sized graphene grains(∼20 µm) were successfully synthesized on polycrystalline copper by rising the growth temperature in the Faraday cage, and showed high quality. Besides, the graphene grown in a Faraday cage exhibits an average current carrier mobility of 309.1 cm2V−1s−1 under room temperature.

Тензостимулированный эффект в легированном и термообработанном кремнии при ориентированной деформации

The tensostimulated effect in heat-treated and doped silicon was investigated. It is shown that uniaxial compression in the [111] direction leads to the decay of thermal donors and the hysteresis development in the dependences of the resistivity on the compression value. It was found that the strain-stimulated effect in manganese-compensated silicon samples is due to simultaneous changes in the concentration and mobility of current carriers.

Effect of substrate temperature on morphology and properties of ZnO:In nanocrystalline films grown by PLD

The purpose of this work is to study the formation regularities of ZnO:In nanocrystalline films grown by pulsed laser deposition (PLD) for application as contact layers of photosensitive elements. It was found that increasing in the substrate temperature from 300 °C to 400 °C the films have a continuous granular structure with a grain size of 9±2 nm and 13.5±4.5 nm, respectively. The sample obtained at the substrate temperature of 150 °C is characterized by the presence of whisker-like structures with 200±47 nm long and 12±8 nm wide on the film’s surface. With increasing substrate temperature from 150 °C to 400 °C, the value of resistivity decreases from 9.3·10−1 Ω·cm to 2.9·10−2 Ω·cm, the concentration of current carriers increases from 2.12·1018 cm−3 to 3.5·1019 cm−3, and the mobility of current carriers also increases from 2.51 cm2/(V·s) to 6.17 cm2/(V·s). The results obtained can be used in the development and manufacture of highly efficient photoelectric converters based on hybrid nanostructures.

High-mobility junction field-effect transistor via graphene/MoS2 heterointerface

Monolayer molybdenum disulfide (MoS2) possesses a desirable direct bandgap with moderate carrier mobility, whereas graphene (Gr) exhibits a zero bandgap and excellent carrier mobility. Numerous approaches have been suggested for concomitantly realizing high on/off current ratio and high carrier mobility in field-effect transistors, but little is known to date about the effect of two-dimensional layered materials. Herein, we propose a Gr/MoS2 heterojunction platform, i.e., junction field-effect transistor (JFET), that enhances the carrier mobility by a factor of ~ 10 (~ 100 cm2 V−1 s−1) compared to that of monolayer MoS2, while retaining a high on/off current ratio of ~ 108 at room temperature. The Fermi level of Gr can be tuned by the wide back-gate bias (VBG) to modulate the effective Schottky barrier height (SBH) at the Gr/MoS2 heterointerface from 528 meV (n-MoS2/p-Gr) to 116 meV (n-MoS2/n-Gr), consequently enhancing the carrier mobility. The double humps in the transconductance derivative profile clearly reveal the carrier transport mechanism of Gr/MoS2, where the barrier height is controlled by electrostatic doping.

Interlayers for Improved Hole Injection in Organic Field‐Effect Transistors

AbstractEfficient charge‐carrier injection is a critical requirement for high‐performance organic electronic devices, such as light‐emitting diodes, solar cells, and field‐effect transistors. In this work, a significantly improved charge‐carrier injection from high work‐function metal‐oxide electrodes in organic field effect transistors (OFETs) is demonstrated for amorphous organic semiconductors (OSCs) by using organic interlayers with a high ionization energy (IE). Molybdenum oxide (MoO3) exhibits limited injection into amorphous 2,2′,7,7′‐tetrakis(N,N‐diphenylamino)‐9,9‐spirobifluorene (Spiro‐TAD) and tris(4‐carbazoyl‐9‐ylphenyl)amine (TCTA) active layers, resulting in high contact resistance and threshold voltage. By inserting an interlayer of a few nanometers thick with high IE between the MoO3 electrode and the amorphous OSC films, the Spiro‐TAD and TCTA OFETs show a substantial enhancement in hole current, subthreshold swing, and effective charge carrier mobility due to the decreased contact resistance. However, for discontinuous interlayers formed on distinct grain domains as in the case of polycrystalline 2,7‐dioctyl[1]benzothieno[3,2‐b][1]benzothiophene (C8‐BTBT) films, the effect of the interlayer reduces. These results demonstrate that the utilization of smooth interlayers with IE higher than the semiconductor is a general approach to elevate the hole injection into amorphous OSCs with high IE in OFETs.

Growth of conjugated semiconductor monocrystals based on benzothienobenzothiophenes from solutions

Organic semiconductors are actively used for numerous applications, their use in flexible electronics technologies is especially promising. The mobility of current carriers is a determining parameter whose value is strongly influenced by the crystallinity and arrangement of molecules in the crystal lattice of the synthesized semiconductor materials. The goal of this work was to obtain thin monocrystal films of conjugated oligothiophene-phenylenes (OTP) structures from solutions and their characterization. In this work, the solvent vapor annealing method was adapted to obtain conjugated structures based on dihexyl- and dioctylbenzothienobenzothiophene (C6-BTBT and C8-BTBT) from dichlorobenzene and toluene solutions with a concentration of 0.06 to 0.80 g / l. Solutions of various concentrations were applied to silicon substrates by centrifugation and droplet method. According to microscopic studies, C8-BTBT single crystals of the required geometry and size of about 1 mm were grown from solutions in toluene with a concentration of less than 0.06 g / l by centrifugation at a speed of 800 rpm. Electrophysical measurements showed that the obtained crystals have hole conductivity with a fairly high carrier mobility up to 0.047 cm2 / V · s (average 0.03 cm2 / V · s), which makes it possible to use these materials for the manufacture of field effect transistors and other electronic devices based on them.

Optimization and Experiments of Lateral Semi-Superjunction Device Based on Normalized Current-Carrying Capability

A lateral double diffused metal oxide semiconductor transistor with the semi-superjunction (semi-SJ LDMOS) is optimized based on the normalized current-carrying capability (CC) and experimentally realized in this letter. The device is fabricated based on an optimized equivalent substrate and the semi-SJ is introduced near the source. The semi-SJ increases the local doping concentration in the N regions meanwhile reduces the current path area and carrier mobility, resulting in the variation of CCs before and after the introduction of the semi-SJ. The normalized CC factor $\eta _{\text {C}}$ is proposed to evaluate this variation, with which the minimum specific on-resistance ${R} _ {\text {ON}, \text {sp}}$ is predicted by the condition of $\eta _{\text {C}}= {1}$ . The experiments of the semi-SJ LDMOS exhibit a minimum ${R} _ {\text {ON}, \text {sp}}$ of 25.5 $\text{m}\Omega \cdot $ cm2 under a breakdown voltage ${V} _{{\text {B}}}$ of 464.3 V. This represents a reduction in ${R} _ {\text {ON}, \text {sp}}$ by 37.7% when compared with the theoretical ${R} _ {\text {ON}, \text {sp}}$ of triple RESURF devices.

Stability of pentacene-based top gate thin film transistor with thick parylene as dielectric under humid environment

This study presents the influence of humidity effect in top gate transistors using pentacene as active layer. The devices are made on a planarized kapton substrate, and 1 μm thick parylene has been used both as gate dielectric and encapsulating layer. Two series of measurement conditions have been used. First, the humidity rate was varied from 0 to 90% in a cell by setting exposure times of 15 min and device characterized, followed to 15 min vacuum. Secondly, humidity rate is fixed at 90% during 144 min and the electrical characteristics recorded successively. The main electrical parameters such as threshold voltage (VT), mobility (μ), on-current (Ion), depletion current (Ioff) and subthreshold slope (S) have been investigated. The results showed that only the electrical parameters in subthreshold region have been affected at different relative humidity (RH) levels for the first series. Under vacuum, the device exhibited stable electrical performances whereas in RH ranging from 24% to 90% we observe an increase of depletion current, and this Ioff increase was found to be reversible. After exposing the device with 90% of RH (second series), from 0 to 108 min in humid environment, threshold voltage, Ion current, VT and charge carrier mobility remain unchanged while Ioff and S are highly affected. Beyond 108 min, Ioff current keeps increasing with a noticeable Ion current degradation. Two effects have to be taken into account: (i) Ioff current increase without any change in on-state regime is the consequence of cumulative effect of Leakage current increase in the parylene dielectric and electrical conductivity increase in pentacene semiconductor, (ii) Ion current decrease is the consequence of absorbed water molecule diffusing and interacting with pentacene. All these parameters are reversible under vacuum after pumping down.

High‐Performance P‐Type Copper(I) Thiocyanate Thin Film Transistors Processed from Solution at Low Temperature

AbstractSemiconducting copper(I) thiocyanate (CuSCN) is actively studied for electronic and optoelectronic applications. Although various kinds of CuSCN‐based transistors are reported, these devices suffer from low charge carrier mobility of about 0.01–0.1 cm2 V−1 s−1. Here, ion gel electrolyte consisting of network polymer and ionic liquid is used as a high capacitance gate insulator to achieve high performance CuSCN‐based electrolyte‐gated transistors (CuSCN‐EGTs) with low operation voltage below 1 V. 30 nm thick CuSCN semiconductor film can be formed by a simple solution process with a low processing temperature (≈100 °C) that is directly applicable to flexible plastic substrates. By doping copper iodide to the CuSCN semiconductor, device performance including drain current and charge carrier mobility of the CuSCN EGT can be improved significantly. The measured charge carrier mobility of ≈0.3 cm2 V−1 s−1 is the highest among the reported CuSCN transistors using various gate insulators. These CuSCN‐EGTs also display good operation stability under continuous quasistatic external gate voltage sweeps. Such superior electrical performance and versatile processability of ion gel–gated CuSCN transistors make them suitable for use in complimentary circuits and large‐area flexible electronics.

Electro-Physical Properties of Ge-doped Cd1-xMnxTe (x < 0.1) Crystals

Ge-doped Cd1-xMnxTe (x = 0.02, 0.04, 0.08) crystals were grown by the Bridgman method. Carried out electrical measurements in the temperature range 280 – 420 K have found that the crystals’ hole conductivity is controlled by the deep compensated acceptors, whose ionization energy (εA) was increased with the content Mn (x) according to the relation εA = 0.6 (1 + 2х) eV. At 300 K: ρ = (108-109) (Ohm´cm), RH = (5×109-5×1010) cm3/C; mobility of current carriers ~ 50 cm2 /(V´s).

High Performance Organic Thin Film Transistors Using Pentacene-Based Rare-Earth Oxide Bilayer Gate Dielectric

High-k dielectrics, neodymium oxide (Nd2O3) and lanthanum oxide (La2O3) are regarded as useful materials to reduce the operating voltage of organic thin film transistors (OTFTs). However, the high-k dielectrics often have the drawback of high interface trap density leading to high leakage current and low carrier mobility. Here, a bilayer La2O3/Nd2O3 gate dielectric for OTFTs is employed to address the issues. A top contact pentacene-based organic thin film transistor is exhibiting a variation in carrier mobility as the thickness of Nd2O3 changes from 100 nm to 175 nm. Compared to the pentacene thin film transistor with solely 118 nm thick La2O3 gate dielectric, the OTFTs with the bilayer La2O3/Nd2O3 (118 nm/150 nm) gate dielectric improves the threshold voltage from − 0.42 V to − 1.1 and V, the carrier mobility from 0.54 cm2/Vs to 1.08 cm2/Vs. These bilayer devices produced the current on–off ratio of 2.4 × 105 and the subthreshold slope of 0.5 V/decade. The OTFT device exhibits good stability under a low voltage bias-stress effect. The OTFTs are investigated in the atomic force microscope to understand the dielectric–pentacene interface to verify the improved OTFT parameters. The morphology and structure of the La2O3/Nd2O3 bilayer dielectric films are studied using a field emission scanning electron microscope and x-ray diffraction techniques.