Specific features of proton interaction with transistor structures having a 2D AlGaN/GaN channel

It has been shown that the interaction of 1 MeV protons at doses of (0.5–2) × 10¹⁴ cm^–2 with transistor structures having a 2D AlGaN/GaN channel (AlGaN/GaN HEMTs) is accompanied not only by the generation of point defects, but also by the formation of local regions with a disordered nanomaterial. The degree of disorder of the nanomaterial was evaluated by multifractal analysis methods. An increase in the degree of disorder of the nanomaterial, manifested the most clearly at a proton dose of 2 × 10¹⁴ cm^–2, leads to several-fold changes in the mobility and electron density in the 2D channel of HEMT structures. In this case, the transistors show a decrease in the source–drain current and an order-of-magnitude increase in the gate leakage current. In HEMT structures having an enhanced disorder of the nanomaterial prior to exposure to protons, proton irradiation results in suppression of the 2D conductivity in the channel and failure of the transistors, even at a dose of 1 × 10¹⁴ cm^–2.     

An investigation of contact resistance between metal electrodes and amorphous gallium-indium-zinc oxide (a-GIZO) thin-film transistors

This paper reports our investigation of different source/drain (S/D) electrode materials in thin-film transistors (TFTs) based on an indium-gallium-zinc oxide (IGZO) semiconductor. Transfer length, contact resistance, channel conductance, and effective resistances between S/D electrodes and amorphous IGZO thin-film transistors were examined. Intrinsic TFT parameters were extracted by the transmission line method (TLM) using a series of TFTs with different channel lengths measured at a low drain voltage. The TFTs fabricated with Cu S/D electrodes showed the lowest contact resistance and transfer length indicating good ohmic characteristics, and good transfer characteristics with intrinsic field-effect mobility (μ_FE-i) of 10.0 cm²/Vs.     

Analysis of the device characteristics of AlGaN/GaN HEMTs over a wide temperature range

In this study, we investigate the behavior of the current–voltage (I–V) characteristics of AlGaN/GaN HEMT in the temperature range of 223–398 K. Temperature dependent device characteristics and the current transport mechanism are reported. It is observed that the Schottky barrier height Φ increases and the ideality factor n decreases with temperature. There is a linear relationship between the barrier height and the ideality factor, which is attributed to barrier height inhomogeneities of AlGaN/GaN HEMT. The estimated values of the series resistances (R_s) are in the range of 144.2 Ω at 223 K to 74.3 Ω at 398 K. The Φ, n, R_s, G_m and Schottky leakage current values are seen to be strongly temperature dependent.     

AlGaN/GaN HEMTs passivated by Cat-CVD SiN Film

We demonstrate the excellent performance of a 140 W AlGaN/GaN HEMT in the C-band, which is passivated by a Cat-CVD SiN film. The interface trap density of the AlGaN surface passivated by Cat-CVD film after NH₃ treatment is 3 × 10¹² cm^− 2, which is the smallest of investigated deposition techniques. The lowest interface trap density achieved by the Cat-CVD technique makes it possible to operate the AlGaN/GaN HEMT in the C-band. We clarify that the Cat-CVD technique is necessary for developing future amplifiers.     

PHEMT as a circuit element for high impedance nanopower amplifiers for ultra-low temperatures application

In this work, high electron mobility transistor (HEMT) was studied as a circuit element for amplifiers operating at temperatures of the order of 10–100 mK. To characterize the HEMT, the relative parameters are proposed to be used. HEMT characteristics were measured at a temperature of 50 mK for the first time. It follows from the reported studies that the power consumption of high-impedance HEMT-based amplifiers can be reduced down to hundreds of nanowatt or even lower.     

Effect of deposition rates on overlay coating structure

Surface alloys were fabricated by the implantation of 25 keV chromium and nickel ions into polycrystalline iron in doses ranging from 1.0 × 10¹⁶ to 4.0 × 10¹⁶ ions cm^-2. The alloy distribution as a function of depth (depth profile) was determined for the Fe-Cr and Fe-Ni surface alloys, and the results were compared with theoretical predictions. The resistance of the surface alloys to environmental attack was evaluated both by determining their anodic polarization behavior under potentiostatic conditions in a buffered boric acid solution and by determining their gaseous oxidation characteristics. The results of the electrochemical studies showed that the general corrosion resistances of the surface alloys are comparable with those of nominally equivalent bulk alloys and that the pitting-corrosion resistances of the surface alloys are superior to that of iron, although generally they are not as good as those of most equivalent bulk alloys. The gaseous oxidation studies showed that surface and bulk Fe-Cr alloys exhibit essentially identical oxidation kinetics, with a much higher rate of oxidation being observed for iron. In both the aqueous corrosion and the gaseous oxidation studies the quantity of the alloying element in the surface alloys was six to seven orders of magnitude less than that in the equivalent bulk alloys.     

N-polar GaN基HEMT准二维电荷传输模型仿真

建立了氮极性(N-polar)GaN基HEMT器件的准二维(Quasi-2-D)电荷传输模型,仿真研究了N-polar GaN基HEMT的直流特性。仿真结果表明,不同的极化效应会对输出特性曲线和转移特性曲线产生不同的影响,考虑自发极化效应(Psp)+压电极化效应(Ppe)、只考虑Ppe和只考虑Psp三种情况下的阈值电压分别为:-3.96V、-2.29V和-2.47V,而其对应的峰值跨导则分别为44mS/mm、41.2mS/mm和41.3mS/mm。该模型为N-polar GaN基HEMT器件仿真提供了理论参考。     

Reduced Graphene Oxide‐Functionalized High Electron Mobility Transistors for Novel Recognition Pattern Label‐Free DNA Sensors

We designed and constructed reduced graphene oxide (rGO) functionalized high electron mobility transistor (HEMT) for rapid and ultra‐sensitive detection of label‐free DNA in real time. The micrometer sized rGO sheets with structural defects helped absorb DNA molecules providing a facile and robust approach to functionalization. DNA was immobilized onto the surface of HEMT gate through rGO functionalization, and changed the conductivity of HEMT. The real time monitor and detection of DNA hybridization by rGO functionalized HEMT presented interesting current responses: a “two steps” signal enhancement in the presence of target DNA; and a “one step” signaling with random DNA. These two different recognition patterns made the HEMT capable of specifically detecting target DNA sequence. The working principle of the rGO functionalized HEMT can be demonstrated as the variation of the ambience charge distribution. Furthermore, the as constructed DNA sensors showed excellent sensitivity of detect limit at 0.07 fM with linear detect range from 0.1 fM to 0.1 pM. The results indicated that the HEMT functionalized with rGO paves a new avenue to design novel electronic devices for high sensitive and specific genetic material assays in biomedical applications.     

Switching voltage, dynamic power dissipation and on-to-off conductance ratio of a spin field effect transistor

The metal-insulator-semiconductor (MIS) and high electron mobility transistor (HEMT) implementations of the spin field effect transistor (SpinFET) proposed by Datta and Das are considered. In both configurations, the SpinFET's switching voltage (for switching on or off) and power dissipation are found to be larger than those of the traditional MISFET or HEMT if the channel length is les 90 nm. This is a consequence of the fact that spin orbit interaction strengths in semiconductors are too weak to impart any significant advantage to the SpinFET. The issue of non-ideal spin injection and detection at the source and drain contacts is also considered. The SpinFET's on-to-off conductance ratio rapidly degrades with decreasing spin injection/detection efficiency, dropping from infinity (for a one-dimensional channel) to as low as ~9.5, if the spin injection/detection efficiency drops from 100% to 90%. The transconductance has a quadratic dependence on the spin injection efficiency. These analyses are valid at arbitrary temperatures.     

Low Schottky Barrier Black Phosphorus Field‐Effect Devices with Ferromagnetic Tunnel Contacts

Black phosphorus (BP) has been recently unveiled as a promising 2D direct bandgap semiconducting material. Here, ambipolar field‐effect transistor behavior of nanolayers of BP with ferromagnetic tunnel contacts is reported. Using TiO₂/Co contacts, a reduced Schottky barrier <50 meV, which can be tuned further by the gate voltage, is obtained. Eminently, a good transistor performance is achieved in the devices discussed here, with drain current modulation of four to six orders of magnitude and a mobility of μ_h ≈ 155 cm² V^?1 s^?1 for hole conduction at room temperature. Magnetoresistance calculations using a spin diffusion model reveal that the source–drain contact resistances in the BP device can be tuned by gate voltage to an optimal range for injection and detection of spin‐polarized holes. The results of the study demonstrate the prospect of BP nanolayers for efficient nanoelectronic and spintronic devices.     

A study of side gate test structures in InAlAs/InGaAs HEMTs for optoelectronic circuit applications

The InAlAs/InGaAs HEMT is a key electron device used in optoelectronic integrated circuits (OEICs) operating in the 1·3 and 1·5 μm optical wavelength ranges. OEIC performances can be degraded by side-gating effects associated with the HEMT. A side gate current is evidenced and demonstrated to be (i) due to a hole current induced by an impact ionization mechanism into the HEMT InGaAs channel and flowing through the InAlAs buffer layer and (ii) strongly dependent on the side gate test structure geometries and types of contacts. Finally, an optimized structure for monolithic integration is presented together with requirements on the operating point.     

HEMT小信号等效电路参数提取

本文用ＨＥＭＴ小信号等效电路模型,考虑到ＨＥＭＴ与ＭＥＳＦＥＴ结构上的不同点,肉体分析了ＨＥＭＴ小信号等效电路中串电阻、寄生电感、寄生电容和本征元件参数的提取和这些方法,提取了ＨＥＭＴ器件３２－３９ＧＨＺ八个频率点的Ｓ参数值。实验结果表明,该方法简单有效,具有可操作性。     

High-performance multilayer WSe2 p-type field effect transistors with Pd contacts for circuit applications

WSe₂ is thought to be one of the best emerging p-type transition metal dichalcogenide (TMD) materials for potential low-power complementary metal oxide semiconductor (CMOS) circuit applications. However, the contact barrier and the interface quality hinder the performance of p-type field effect transistors (FETs) with WSe₂ films. In this work, metals with different work functions—Pd, Pt, and Ag—were systematically investigated as contacts for WSe₂ to decrease the contact resistances at source/drain electrodes and potentially improve transistor performance. Optimized p-type multilayer WSe₂ FETs with Pd contacts were successfully fabricated, and excellent electrical characteristics were obtained: a hole mobility of 36 cm²V^?1 s^?1; a high on/off ratio, over 10⁶; and a record low sub-threshold swing, SS?=?95 mV/dec, which may be attributed to the small Schottky barrier height of 295 meV between Pd and WSe₂, and strong Fermi-level pinning near the top of the valence band at the interface. Finally, a full-functional CMOS inverter was also demonstrated, consisting of a p-type WSe₂ FET together with a normal n-type MoS₂ FET. This confirmed the potential of TMD FETs in future low-power CMOS digital circuit applications.

     

Determination of thermophysical characteristics of high heat-conductance materials on thin samples

A method is proposed that makes it possible to eliminate the contact thermal resistances in the determination of the thermophysical characteristics of high heat conductance materials on samples with thickness h5 · 10^–3 m.Translated from Inzhenerno-Fizicheskii Zhurnal Vol. 29, No. 6, pp. 1049–1056, December, 1975.     

Porous silicon based negative electrodes for lithium ion batteries

Various structures of macroporous silicon intended for the fabrication of lithium ion battery anodes have been studied. Macroporous membranes were prepared by the photoelectrochemical etching of n-type silicon wafers possessing various resistances, followed by the removal of the substrate. The porosity was increased via additional oxidation with the subsequent etching of oxide. The electric contacts on the membrane were fabricated by depositing copper with a titanium sublayer and soldering the structure to a supporting molybdenum disk. The electrochemical characteristics of anodes were studied in a cell with a lithium counterelectrode. These measurements showed that the obtained porous silicon electrodes possess a high capacity for lithium insertion (up to 50 mAh/cm²) and admit more than 20 charge/discharge cycles.     

Experimental investigation of 3-W class-AB cryogenically-cooled amplifier employing GaN HEMT for front end receivers of mobile base stations

This paper presents experimental results of a 2-GHz band gallium nitride high electron mobility transistor (GaN HEMT) amplifier cryogenically-cooled to 60 K as a part of the cryogenic receiver front end (CRFE) for mobile base station receivers. At a temperature of 60 K, the GaN HEMT amplifier attains the maximum power added efficiency of 62%, the saturation output power of 35 dBm, the gain of 26 dB, and the noise figure of 2.6 dB when operating at class-AB biasing. The results reported herein are the first on the performance of a cryogenically-cooled GaN HEMT amplifier aiming at use in a 2-GHz band CRFE.     

Study on Li-ion diffusion in nano-crystalline LiMn2O4 thin film cathode grown by pulsed laser deposition using CV, EIS and PITT techniques

In the present work, LiMn₂O₄ thin films have been prepared by pulsed laser deposition on stainless steel substrates. The films deposited at 400 °C and 200 mTorr of oxygen were mainly composed of nano-crystals less than 100 nm and their agglomerates. Three different electrochemical methods including CV, EIS and PITT were applied to measure the overall Li⁺-ion diffusion coefficients and charge-transfer resistances at various potentials from 3.85 to 4.5 V. The Li⁺ diffusion coefficients were in the range of 10⁻¹² to 10⁻¹⁰ cm² s⁻¹, depending on the potentials. It was found that the charge-transfer resistances decreased with the increase of potentials. Especially, relatively high diffusion coefficients and low charge-transfer resistances were observed above 4.2 V.     

Comparison of Ohmic contact resistances of n- and p-type Ge source/drain and their impact on transport characteristics of Ge metal oxide semiconductor field effect transistors

We report the results of a systematic study to understand low drive current of Ge-nMOSFET (metal-oxide-semiconductor field-effect transistor). The poor electron transport property is primarily attributed to the low dopant activation efficiency and high contact resistance. Results are supported by analyzing source/drain Ohmic metal contacts to n-type Ge using the transmission line method. Ni contacts to Ge nMOSFETs exhibit specific contact resistances of 10^− 3-10^− 5 Ω cm², which is significantly higher than the 10^− 7-10^− 8 Ω cm² of Ni contacts to Ge pMOSFETs. The high resistance of Ni Ohmic contacts to n-type Ge is attributed mainly to insufficient dopant activation in Ge (or high sheet resistance) and a high tunneling barrier. Results obtained in this work identify one of the root causes of the lower than expected Ge nMOSFET transport issue, advancing high mobility Ge channel technology.     

Effective Thermal-Conductivity Measurements on Supporting Structures of the Mercury Probe Bepi Colombo

Measurements were done on a carbon fiber reinforced composite (CFC) sample tested for the space probe Bepi Colombo by using the guarded hot-plate (GHP) method. The values of interest were the thermal transmittance through the samples, (56.3 ± 3.6) W · m^?2 · K^?1, and the effective thermal conductivity (1.06 ± 0.07) W · m^?1 · K^?1. The samples consist of a light honeycomb core attached to thicker surface plates. Due to this construction, the effective thermal conductivity parallel to the face plates is higher than the effective thermal conductivity through the sample. This leads to lateral heat gains or losses during the GHP measurement, which in return can lead to erroneous results. Furthermore, due to the high rigidity of the CFC material, there will be high contact resistances between the samples and the GHP apparatus plates. The separation of these thermal contact resistances from the total measured thermal resistance is essential in order to achieve correct results. Good results were achieved using a special measurement setup and a lateral correction method designed to reduce errors due to lateral heat flows.     

The influence of an In<Subscript>0.52</Subscript>Al<Subscript>0.48</Subscript>As transition layer design on the transport characteristics of a metamorphic high-electron-mobility transistor

We have used the atomic force microscopy and Hall effect measurements to study the influence of In_0.52Al_0.48As transition layer design on the electron mobility in the InAlAs/InGaAs/GaAs channel of a highelectron- mobility transistor (HEMT) with the metamorphic buffer. The optimum buffer layer favors suppression of the misfit dislocation threading into upper layers of the HEMT heterostructure and prevents development of the surface microrelief.