沟道电场分布对AlN/GaN HFETs极化库仑场散射的影响

Based on the measured capacitance–voltage(C–V) curves and current–voltage(I–V) curves for the prepared differently-sized Al N/Ga N heterostructure field-effect transistors(HFETs), the I–V characteristics of the Al N/Ga N HFETs were simulated using the quasi-two-dimensional(quasi-2D) model. By analyzing the variation in the electron mobility for the two-dimensional electron gas(2DEG) with the channel electric field, it is found that the different polarization charge distribution generated by the different channel electric field distribution can result in different polarization Coulomb field(PCF) scattering. The 2DEG electron mobility difference is mostly caused by the PCF scattering which can reach up to 899.6 cm2/(V s)(sample a), 1307.4 cm2/(V s)(sample b),1561.7 cm2/(V s)(sample c) and 678.1 cm2/(V s)(sample d), respectively. When the 2DEG sheet density is modulated by the drain–source bias, the electron mobility for samples a, b and c appear to peak with the variation of the 2DEG sheet density, but for sample d, no peak appears and the electron mobility rises with the increase in the2 DEG sheet density.     

Improving solution-processed n-type organic field-effect transistors by transfer-printed metal/semiconductor and semiconductor/semiconductor heterojunctions

Solution-processed n-type organic field effect transistors (OFETs) are in need of proper metal contact for improving injection and mobility, as well as balanced hole mobility for building logic circuit units. We address the two distinct problems by a simple technique of transfer-printing. Transfer-printed Au contacts on a terrylene-based semiconductor (TDI) significantly reduced the inverse subthreshold slope by 5.6 V/dec and enhanced the linear mobility by over 5 times compared to evaporated Au contacts. Hence, devices with a high-work-function metal (Au) are comparable with those with low-work-function metals (Al and Ca), indicating a fundamental advantage of transfer-printed electrodes in electron injection. We also transfer-printed a poly(3-hexylthiophene) (P3HT) layer onto TDI to construct a double-channel ambipolar transistor by a solution process for the first time. The transistor exhibits balanced hole and electron mobility (3.0 × 10⁻³ and 2.8 × 10⁻³ cm² V⁻¹ s⁻¹) even in a coplanar structure with symmetric Au electrodes. The technique is especially useful for reaching intrinsic mobility of new materials, and enables significant enlargement of the material tanks for solution-processed functional heterojunction OFETs.     

Microwave performance of AlGaN/GaN metal insulator semiconductorfield effect transistors on sapphire substrates

Metal-insulator-semiconductor field effect transistors (MISFETs) from surface-passivated undoped AlGaN/GaN heterostructures on sapphire were fabricated. Measured static output characteristics includes full channel currents (I_dss) of roughly 750 mA/mm with gate-source pinchoff voltages of -10 V and peak extrinsic transconductancies (g_m) of 100-110 mS/mm. Increased surface roughness resulting from a gate recess process to reduce the pinchoff voltage introduces gate leakage currents in the micro-amps regime. With evidence for reduced dc-to-rf dispersion from pulsed gate transfer characteristics, these devices at 4 GHz with 28.0 V bias generated maximum output power densities of 4.2 W/mm with 14.5 dB of gain and 36% power added efficiency     

A silicon-on-insulator metal–semiconductor field-effect transistor with an L-shaped buried oxide for high output-power density

We describe a novel silicon-on-insulator metal–semiconductor field-effect transistor with an L-shaped buried oxide (LB-SOI MESFET) and its maximum output power density (P_max). To optimize the surface electric field and improve the breakdown voltage, we eliminated part of the oxide and replaced it with n-type silicon. By creating an n⁺–n region on the source side and modifying the electric field distribution, the breakdown voltage improved by 42% compared to a conventional device. Channel control is realized by varying the depletion layer width underneath the metal gate contact. This modulates the thickness of the conducting channel and thus controls the current between the source and the drain. Continuation of the n-type silicon on top of the buried oxide after the gate metal changes the depletion layer and increases the total channel charge for conduction, so the drain current increases by a factor of five compared to a conventional SOI MESFET. In addition, P_max is increased by a factor of 17.7 with respect to a conventional structure, which is important for large-signal analog applications. Consequently, our novel LB-SOI MESFET has superior electrical characteristics.     

题目：AlGaN/GaN异质结电容与电导色散研究

The dispersion mechanism in Al0:27Ga0:73N/GaN heterostructure was investigated using frequencydependent capacitance and conductance measurements.It was found that the significant capacitance and conductance dispersion occurred primarily for measurement frequency beyond 100 kHz before the channel cutoff at the interface,suggesting that the vertical polarization electrical field under the gate metal should be closely related with the observed dispersive behavior.According to the Schottky-Read-Hall model,a traditional trapping mechanism cannot be used to explain our result.Instead,a piezoelectric polarization strain relaxation model was adopted to interpret the dispersion.By fitting the obtained capacitance data,the corresponding characteristic time and charge density were determined 10..8 s and 5.26 1012 cm..2 respectively,in good agreement with the conductance data and theoretical prediction.     

Cardanol-based polymeric gate dielectric for solution-processed organic field-effect transistors on flexible substrates

A cardanol-based polymer, poly(2-hydroxy-3-cardanylpropyl methacrylate) (PHCPM), was utilized as the gate dielectric of an organic field-effect transistor (OFET). PHCPM has good surface properties, appropriate gate dielectric characteristics, and good compatibility with solution-processed semiconducting polymers. The electrical properties of an FET that was prepared with natural resource-based PHCPM as a gate dielectric layer and solution-processed poly[2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT) as a semiconducting layer were investigated on flexible substrates. The flexible PBTTT-OFET device with the PCHPM gate dielectric exhibited high mobility and reliable performance, even in the bending state, without significant hysteresis.     

边欧姆工艺对AlN/GaN 异质结场效应晶体管极化梯度库仑场散射的影响

Using the measured capacitance–voltage and current–voltage characteristics of the rectangular Al N/Ga N heterostructure field-effect transistors(HFETs) with the side-Ohmic contacts, it was found that the polarization Coulomb field scattering in the Al N/Ga N HFETs was greatly weakened after the side-Ohmic contact processing, however, it still could not be ignored. It was also found that, with side-Ohmic contacts, the polarization Coulomb field scattering was much stronger in Al N/Ga N HFETs than in Al Ga N/Al N/Ga N and In0:17Al0:83N/Al N/Ga N HFETs, which was attributed to the extremely thinner barrier layer and the stronger polarization of the Al N/Ga N heterostructure.     

Electrical characteristics of AlGaN/GaN HEMTs on 4-in diameter sapphire substrate

AlGaN/GaN high-electron-mobility transistors (HEMTs) were fabricated and the uniformity of dc properties were studied for the first time on 4-in diameter sapphire substrate. A quarter of 4-in diameter AlGaN/GaN epitaxial wafer was used for the uniformity studies of HEMTs. The observed average maximum drain current density, extrinsic transconductance and threshold voltage values for HEMTs were 515 mA/mm, 197 mS/mm, and -2.30 V with standard deviations 9.34%, 4.82%, and 6.52%, respectively. The uniformity of Hall mobility across the 4-in wafer was 1322 cm/sup 2//Vs with a standard deviation of 4.27%. The uniformity of sheet resistance across 4-in diameter wafer, measured using Hall Effect was 575 /spl Omega//sq. with a standard deviation 9.01%. The uniformity of HEMTs dc properties are in good correlation with the electrical characteristics of AlGaN/GaN heterostructures, which was obtained from the Hall Effect and capacitance-voltage (C-V) measurements.     

基于FC技术的AlGaN/GaN HEMT

采用FC技术将管芯倒扣至AlN基板散热的AlGaN/GaN HEMTs,并通过热阻模型分析了FC方式的散热机理．从测试结果看,器件的热阻可大幅降到14.9K·mm/W,直流特性明显增加,饱和电流提高33％．表明采用FC技术有效改善了器件散热,而且引入的寄生电感较小,可获得更大输出功率．如果进一步完善频率特性的优化,可以加快FC技术的AlGaN/GaN大功率HEMT器件的实用化进程．     

A study of temperature field in a GaN heterostructure field-effect transistor

This paper presents a three-dimensional finite element based heat transfer model for a Gallium Nitride-based Heterostructure Field-Effect Transistor (henceforth referred to as GaN HFET). Analyses were carried out to study the distribution of temperature in the HFET under steady-state conditions for two different steady-current inputs. Two different substrates for the HFET, sapphire and silicon carbide (SiC), were studied. The paper discusses the effect of using a heat sink and also that of using reasonable contact resistances on the substrate side of the HFET, on the temperature profile. In all cases, the gate region of the HFET was found to attain the highest temperature. Subsequent experiments to validate the results of the computational analysis were carried out at the Oakridge National Laboratories, Knoxville, and are also presented in this paper.     

Unpassivated GaN/AlGaN/GaN power high electron mobility transistors with dispersion controlled by epitaxial layer design

In this paper, a novel GaN/AlGaN/GaN high electron mobility transistor (HEMT) is discussed. The device uses a thick GaN-cap layer (∼250 nm) to reduce the effect of surface potential fluctuations on device performance. Devices without Si₃N₄ passivation showed no dispersion with 200-ns-pulse-width gate-lag measurements. Saturated output-power density of 3.4 W/mm and peak power-added efficiency (PAE) of 32% at 10 GHz (V_DS=+15 V) were achieved from unpassivated devices on sapphire substrates. Large gate-leakage current and low breakdown voltage prevented higher drain-bias operation and are currently under investigation.     

蓝宝石衬底AlGaNöGaN 功率HEM Ts 研制

基于蓝宝石衬底的高微波特性 Al Ga N/Ga N HEMTs功率器件 ,器件采用了新的欧姆接触和新型空气桥方案。测试表明 ,器件电流密度 0 .784A/mm,跨导 1 97m S/mm,关态击穿电压 >80 V,截止态漏电很小 ,栅宽 1 mm的器件的单位截止频率 ( f T)达到 2 0 GHz,最大振荡频率 ( fmax) 2 8GHz,2 GHz脉冲测试下 ,栅宽 0 .75 mm器件 ,功率增益1 1 .8d B,输出功率 3 1 .2 d Bm,功率密度 1 .75 W/mm。     

Effect of UV-ozone oxidation on the device characteristics of InP-based heterostructure bipolar transistors

In this letter, we report the effect of UV-ozone treatments on the electrical characteristics of InGaAs/InP heterostructure bipolar transistors (HBTs). For treatments of less than 10 min, the HBT’s current gain increased with the UV-ozone exposure. This improvement is attributed to a passivation of the extrinsic base. For exposures longer than 10 min, the current gain is reduced. An increase of the base collector leakage current, leading to a degradation of the HBT’s breakdown voltage, was observed after only about 2 min of UV-ozone treatment.     

多栅指AlGaN/GaN HEMT器件自热效应研究

Self-heating in multi-finger AlGaN/GaN high-electron-mobility transistors(HEMTs) is investigated by measurements and modeling of device junction temperature under steady-state operation.Measurements are carried out using micro-Raman scattering to obtain the detailed and accurate temperature distribution of the device.The device peak temperature corresponds to the high field region at the drain side of gate edge.The channel temperature of the device is modeled using a combined electro-thermal model considering 2DEG transport characteristics and the Joule heating power distribution.The results reveal excellent correlation to the micro-Raman measurements, validating our model for the design of better cooled structures.Furthermore,the influence of layout design on the channel temperature of multi-finger AlGaN/GaN HEMTs is studied using the proposed electro-thermal model, allowing for device optimization.     

Top-gate organic field-effect transistors fabricated on paper with high operational stability

We report on top-gate organic field-effect transistors (OFETs) fabricated on specialty paper, PowerCoat™ HD 230 from Arjowiggins Creative Papers coated with a buffer layer composed of a polyvinyl alcohol (PVA) and polyvinylpyrrolidine (PVP) blend. OFETs operate at low voltages and display average carrier mobility values of 1.7 ± 1.1 × 10⁻¹ cm²/Vs, average threshold voltage values of −1.4 ± 0.2 V, and average on/off current ratio of 10⁵. OFETs also display excellent operational stability demonstrated by stable 1000 scans of the transfer characteristics and by stable on-currents displaying less than 6% change during a DC bias stress test at V_DS = V_GS = −10 V for 1 h. Furthermore, OFETs on paper display a decrease of only 7% in their on-state current during a bending test. The performance of these OFETs on paper is comparable to that displayed by top-gate OFETs with the same geometry fabricated on glass substrates.     

Transport properties of AlGaN/GaN metal–oxide–semiconductor heterostructure field-effect transistors with Al2O3 of different thickness

The Al₂O₃ as a gate oxide and passivation was used to study the transport properties of AlGaN/GaN metal–oxide–semiconductor heterostructure field-effect transistors (MOSHFETs). Performance of the devices with Al₂O₃ of different thickness between 4 and 14 nm prepared by metal–organic chemical vapor deposition (MOCVD) and with 4 nm thick Al₂O₃ prepared by Al sputtering and oxidation was investigated. All MOS-devices yielded higher transconductance than their HFET counterparts, i.e. the transconductance/capacitance expected proportionality assuming the same carrier velocity was not fulfilled. A different electric field near/below the gate contact due to a reduction of traps is responsible for the carrier velocity enhancement in the channel of the MOSHFET. The trap reduction depends on the oxide used, as follows from the capacitance vs frequency dispersion for devices investigated. It is qualitatively in a good agreement with the different velocity enhancement evaluated, and devices with thinner oxide show higher traps reduction as well as higher transconductance enhancement. It is also shown that obtained conclusions can be applied well on performance of SiO₂/AlGaN/GaN MOSHFETs.     

High performance lead phthalocyanine films and its effect on the field-effect transistors

The film morphology, structure, and electrical properties of lead phthalocyanine (PbPc) epitaxially grown on 5,5″-bis(3′-fluoro-biphenyl-4-yl)-2,2′:5′,2″-terthiophene (m-F2BP3T) inducing layer substrates were systematic investigated. The morphologies of PbPc films sensitively depend on the thickness of the inducing layer and substrate temperature. All the epitaxial PbPc films with high quality presented the triclinic form with a variation of the out-of-plane orientation. The field-effect mobility of the epitaxial PbPc films was 0.05–0.31 cm²/V s, which was significantly improved by 1–2 orders of magnitude compared to the traditional films. The evolution of the device performance is the synergistic effect of the morphology and out-of-plane orientation of the triclinic form of PbPc. The higher quality of the films and the smaller ratio of (1 0 0)/(0 0 1), the higher device performance is. A clear relationship between the morphology, structure, and the performance of epitaxial PbPc-based organic field-effect transistors was reported.     

Stable growth of large-area single crystalline thin films from an organic semiconductor/polymer blend solution for high-mobility organic field-effect transistors

We developed an effective and steady solution-processing technique for a small molecule–type semiconductor, C₁₀–DNBDT–NW, by adding an amorphous PMMA polymer to produce stable growth of a two-dimensional large-area single-crystalline thin film by effective phase separation at a crucially faster processing speed compared to the case without the addition of a polymer. By using this solution-processing technique, it is noteworthy that the single-crystalline films of C₁₀–DNBDT–NW/PMMA exhibit the highest and average mobilities of 17 and 10.6 cm²/Vs, respectively. Furthermore, we also show the limitations of two-dimensional continuous growth of a single-crystalline film in terms of the solution technique.     

Incorporation of dielectric layers into the processing of III-nitride-based heterostructure field-effect transistors

Dielectric layers within III-nitride transistor technology can act either as passivation layers or as gate-dielectric layers. In this paper, we reflect on both issues and present novel approaches of dielectric schemes. In both cases, the elimination of surface traps or, more generally, of surface states is a key issue in obtaining improved device performance. As gate dielectrics, we introduced and investigated thermally and photoelectrochemically generated Al_xGa_2−xO₃, SiO₂, the combination of Al_xGa_2−xO₃ and SiO₂ (tandem-dielectric stack), and e-beam-deposited Al₂O₃. These dielectric layers serve simultaneously as a passivation layer. In addition, we introduced plasma-enhanced chemical-vapor deposition (PECVD)-deposited SiN_x for passivation. The results highlight the importance of passivation and the introduction of gate dielectrics and emphasize the relationship between surface states and improved direct-current (DC) performance. Backed by additional measurements, we proposed a different gateleakage mechanism for heterostructure field-effect transistor (HFET) and metal-oxide semiconductor heterostructure field-effect transistor (MOSHFET) devices.     

Characterization of developing source/drain current of carbon nanotube field-effect transistors with n-doping by polyethylene imine

An unsteady source/drain current induced by the source/drain bias of the n-type carbon nanotube field-effect transistors (n-CNTFETs), based on networked SWNTs, is reported. This current might affect the usual source/drain current regulated by the specified gate voltage and even overweighs the devices’ n-type characteristics. Through doping with polyethylene imine (PEI), the n-type devices here are made from the p-CNTFETs that were fabricated by printing interconnected CNTs between electrodes using the newly proposed laser transfer printing technique. To properly preserve the n-characteristics, devices with the PEI thickness less than 40 nm and with operating source/drain voltage below 0.5 V are recommended.