Prospects for the development of high-power field-effect transistors based on heterostructures with donor-acceptor doping

We report the first results on the development of high-power field-effect transistors on gallium-arsenide heterosrtuctures with a quantum well and additional potential barriers, formed from layers with different doping types, optimized to reduce transverse spatial electron transport and enhance quantum confinement. The transistors yield a doubled output power at a trapezoidal gate length of 0.4–0.5 μm and a total gate width of 0.8 mm at a frequency of 10 GHz in the continuous mode of operation. The gain exceeds 9.5 dB at a specific output power above 1.6 W/mm and a power-added efficiency of up to 50%. Prospects for the development of such devices are presented.     

Frequency limits of GaAs and InP field-effect transistors at 300 K and 77 K with typical active-layer doping

InP FET's with active layer doping of 10¹⁷donors/ cm³have limiting values of fTroughly fifty per cent higher than those of equivalent GaAs devices for lengths ranging from 0.5 µm to 3 µm at 300 K, and from eighty percent to forty percent higher in this gate length range at 77 K.     

Frequency limits of GaAs and InP field-effect transistors

Monte Carlo calculations of electron transport in InP and GaAs short-channel field-effect transisters (FET's) show that a significant departure from the equilibrium velocity-field curve occurs in these devices. On the basis of these calculations, InP FET's should have high-frequency performance superior to that of GaAs FET's only for effective channel lengths in excess of 1.5 µ.     

Influence of nonuniform field distribution on frequency limits of GaAs field-effect transistors

A simple model which describes well the nonequilibrium electron transport in GaAs using the fit to the equilibrium Monte Carlo data is suggested. In the frame of this model, the cutoff-frequency/gate-length curves are calculated for uniform and nonuniform channel field distribution in GaAs f.e.t.s. The results show that the nonhomogeneity of the electric field in the channel can considerably decrease (by 30%) the maximal frequency of GaAs f.e.t.s.     

Study of the effect of the gate region parameters on static characteristics of microwave field-effect transistors based on pseudomorphic AlGaAs-InGaAs-GaAs heterostructures

The results of numerical simulation and experimental study of the effect of the gate region parameters on static characteristics of microwave field-effect transistors based on pseudomorphic AlGaAs-InGaAs-GaAs heterostructures (p-HEMT) are considered. The possibility of correct simulation of static characteristics of actual device structures of p-HEMT transistors using the TCAD software package (SILVACO Inc.) is demonstrated. The essential necessity of using selective gate-groove etching to achieve controllable and reproducible device parameters is shown.     

Comparison of simple models of cylindrical and plane field-effect transistors

The electrical properties of plane field-effect transistors with different assumed impurity-atom distributions in their channel regions, corresponding to either an alloyed- or a diffused-gate p-n junction, are compared with those of the cylindrical type, with a uniform distribution of impurities in the channel. It is shown that the electrical properties of different types of field-effect transistors with the same pinchoff voltage and transconductance are quite similar.     

Effect of electron-donating unit on crystallinity and charge transport in organic field-effect transistors with thienoisoindigo-based small molecules

We report the effect of an electron-donating unit on solid-state crystal orientation and charge transport in organic field-effect transistors (OFETs) with thienoisoindigo (TIIG)-based small molecules. End-capping of different electron-donor moieties [benzene (Bz), naphthalene (Np), and benzofuran (Bf)] onto TIIG (giving TIIG-Bz, TIIG-Np, and TIIG-Bf) is resulted in different electronic energy levels, solid-state morphologies and performance in OFETs. The 80 °C post-annealed TIIG-Np OFETs show the best device performance with a best hole mobility of 0.019 cm² V⁻¹ s⁻¹ and threshold voltage of −8.6 ± 0.9 V using top gate/bottom contact geometry and a CYTOP gate dielectric. We further investigated the morphological microstructure of the TIIG-based small molecules by using grazing incidence wide angle X-ray scattering, atomic force microscopy and a polarized optical microscope. The electronic transport levels of the TIIG-based small molecules in thin-film states were investigated using ultraviolet photoelectron spectroscopy to examine the charge injection properties of the gold electrode.     

Flexible organic field-effect transistors based on electrospun conjugated polymer nanofibers with high bending stability

We report on flexible, single electrospun nanofiber field-effect transistors made by a blend of poly(3-decylthiophene) and poly(3-hexylthiophene), assessing for the first time the performances of this class of devices in terms of stability upon repeated tensile bending. Charge-carrier mobilities in the nanofiber-based device are estimated of the order of 10⁻³ cm²/(V s). Repeated cycles of bending and relaxing are performed, and the evolution of the device current–voltage characteristics is monitored up to 1000 cycles. We find that during bending the mobility is higher than that measured in planar conditions, and that after about 100 bending cycles it rapidly stabilizes. The here observed bending stability suggests a high compatibility of electrospun nanofibers with devices fabricated by roll-to-roll processes, and with bendable or wearable electronics.     

Solution-processed low leakage organic field-effect transistors with self-pattern registration based on patterned dielectric barrier

We demonstrated a new type of a solution-processed organic field-effect transistor (OFET) in a bottom-gate, top-contact geometry where low leakage current and self-pattern registration were achieved using a patterned dielectric barrier (PDB). The PDB of a hydrophobic fluorinated-polymer was produced on the top of a polymeric gate insulator of poly(4-vinylphenyl) by transfer-printing. The PDB enables to effectively screen out the vertical charge flow generated from the gate electrode, and thus the vertical leakage current between the gate and the drain was reduced by two orders of the magnitude compared to the leakage current in a conventional OFET without the PDB. Moreover, the PDB defines spontaneously an active channel pattern from a solution of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS PEN) by means of the selective wettability and the geometrical confinement.     

Organic field-effect transistors based on low-temperature processable transparent polymer dielectrics with low leakage current

A solution-based transparent polymer was investigated as the gate dielectric for organic field-effect transistors (OFETs). Organic thin films (400 nm) are readily fabricated by spin-coating a polyhydrazide solution under ambient conditions on the ITO substrates, followed by annealing at a low temperature (120 °C). The smooth transparent dielectrics exhibited excellent insulating properties with very low leakage current densities of ～10^?8 A/cm². High performance OFETs with evaporated pentacene as organic semiconductor function at a low operate voltage (?15 V). The mobility could reach as high as 0.7 cm²/Vs and on/off current ratio up to 10⁴. Solution-processed TIPS-pentacene OFETs also work well with this polymer dielectric.     

Organic field-effect transistors based on J-aggregate thin films of a bisazomethine dye

We report on the fabrication and the characterization of p-type organic field-effect transistors based on vapor-deposited J-aggregate bisazomethine dye thin films. The absorption spectra of this non-ionic organic semiconductor in the solid state show a strong influence of the film thickness on the J-aggregate formation. However, the electrical characteristics of the devices demonstrate that the hole transport properties do not vary significantly in films thicker than 100 nm. This is due to the fact that the J-aggregates are formed in this material at the surface of the crystalline grains and do not influence the semiconductor/gate dielectric interface and the charge transport properties of the devices. Hole field-effect mobilities as high as 2.4 × 10^?4 cm² V^?1 s^?1 were obtained and could be slightly improved by a solvent vapor treatment due to changes in the film crystallinity. Overall, this study demonstrates that J-aggregate bisazomethine dye thin films are good candidates for the realization of organic electronic devices.     

High density 2DEG in III-V semiconductor heterostructures and high-electron-mobility transistors based on them

Situation in high-electron-mobility transistor (HEMT) technology is discussed. The N-AlGaAs/InGaAs/GaAs pseudomorphic HEMT’s are now considered as most advanced for mmwave monolithic circuits, but metamorphic N-In_xAl_1−x As/In_yGa_1−y As/In_xAl_1−x As HEMT’s grown on GaAs substrates are very promising for the future high-frequency devices. High density 2DEG in HEMT’s is analyzed by means of the Hall effect and photoluminescence measurements. Processing technology of the sub-0.25-μm pseudomorphic HEMT’s, metamorphic HEMT’s and their characteristics are also described. Fiz. Tekh. Poluprovodn. 33, 1064–1065 (September 1999) This article was published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Base transport factor calculations for transistors with complementary error function and Gaussian base doping profiles

By taking account of the carrier mobility degradation at high impurity concentrations, the high-frequency base transport factor of an n-p-n germanium base transistor was computed numerically for different base doping levels. The doping profiles under consideration were Gaussian and complementary error functions. The base doping level adjacent to the emitter was optimized for minimum base transit time. The optimum values are 4×10¹⁷atom/ cm³for complementary error function profile and 2×10¹⁷atom/cm³for Gaussian profile. The effects of emitter barrier capacitance, base resistance, collector barrier capacitance, and the collector depletion layer on the overall frequency response of a junction transistor are also discussed.     

On the delta-type doping of GaAs-based heterostructures with manganese compounds

Heterostructures, which incorporate GaAs/InGaAs/GaAs quantum wells and are doped with spatially remote monatomic Mn layers, are formed on GaAs(001) substrate under conditions of multilayer buildup by the method of molecular-beam epitaxy. Combined studies of the obtained samples were performed by the method of secondary-ion mass spectrometry, by measurements of X-ray diffraction, and using a transmission electron microscope. The heterostructures under study with a doping impurity concentration amounting to 0.5 single layers are elastically stressed and demonstrate planar clearly defined interfaces without visible extended or point defects. A method for visualization of the distribution of the manganese concentration in the three-dimensional GaAs matrix in the vicinity of a quantum well is suggested. According to experimental results, there is a probability for manganese diffusion into the GaAs/InGaAs/GaAs quantum well when the critical thickness of the GaAs buffer layer is decreased to a value smaller than 3 nm.     

Ways and peculiarities of submillimeter wavelength detection with short-channel field-effect transistors

The detection properties of some short-channel field-effect transistors (FETs) have been analyzed using the steady-state output characteristics of these devices. The calculated dependences of voltage—power sensitivity on applied voltage are compared with the corresponding curves obtained from high-frequency measurements. It is shown that the nonmonotonic dependence of the FET photosensitivity on gate voltage that is observed in the frequency range of 400–750 GHz is not related to resonant excitation of 2D plasmons in the subgate plasma but is due to the change in the distribution of stationary fields in the structure and, as a result, to the change in the efficiency of nonresonant nonlinearity procedures in the transistor’s electron subsystem with an increase in the gate-channel voltage. This conclusion is confirmed by analysis of the frequency dependences of photoresponse in the range under consideration, which do not exhibit resonant behavior at the frequencies corresponding to the peaks in the curves measured at a fixed frequency and different gate voltages.     

Controlling the crystal formation in solution-process for organic field-effect transistors with high-performance

We control the growth of high-quality organic semiconducting crystals in the aim of transistor application. By finely tuning the processing parameters, both isolated crystals showing characteristic facet angles and irregular-shaped, thin crystalline domains are obtained in large sizes (>400 μm). Structural investigations indicate that the various shapes of crystals are in the same crystal structure, and reveal that the irregular-shaped crystalline domains are composed by terrace of molecularly flat regions, which can be up to hundreds of microns in size. When applied in field-effect transistors, the thin crystalline domains exhibit the best performance showing μ_FET up to 4.4 cm²/V s. This is an order of magnitude higher than that of the transistors made from as-spun films and thick crystals. The approach well demonstrates the importance of fine control of crystal formation and can be generally used for getting organic crystal transistors.     

Generation-recombination noise in the channel of GaAs Schottky-gate field-effect transistors

The low-frequency noise in GaAs m.e.s. f.e.t.s was measured continuously for temperatures varying from 80 to 310K. It presented distinct maxima, suggesting the presence of several g.r. processes. The shift of these peaks at different frequencies (500 Hz to 1 MHz) allowed us to obtain the time constants and the activation energies of four trapping levels. The noise reported here could stem from multilevel trapping in the channel.     

Transient radiation effects in microwave monolithic integrated circuits based on heterostructure field-effect transistors: Experiment and model

The results of experimental studies and simulations of transient radiation effects in microwave monolithic integrated circuits, based on heterostructure field-effect transistors, affected by the pulse ionizing radiation, are presented. The physical model, which adequately describes transient radiation effects in field-effect transistors in dose rate range up to 10¹² rad/s, is proposed. Based on the physical model, the equivalent electric circuit, taking into account the dominating ionization effects, intended for using in the computer-aided design (CAD), is constructed. The simulated ionizing responses of the microwave low-noise amplifier (LNA) MIC are in accordance with the experimental data.     

Effects of intervalley scattering on noise in GaAs and InP field-effect transistors

The results of a dynamic analysis of electron transport in GaAs and InP have been used to determine the effects of device cooling, channel length, and frequency of operation on the noise performance of FET's made of these materials. Noise temperature of the material as a function of electric field is first obtained by an analysis that models intervalley scattering using a Monte Carlo calculation method. Noise figure of the intrinsic device is then obtained using a gradual-channel analysis. The validity of such an analysis is discussed. Both GaAs and InP FET's should exhibit very good low-noise performance, with the intrinsic InP device somewhat noisier than the GaAs device at equivalent values of f/fT. For GaAs the intrinsic noise figure can be considerably reduced as the device is cooled, but for InP, cooling from 300 to 77 K should leave intrinsic noise figure almost unchanged.