Ion-implanted Metal-semiconductor Field-effect Transistors Research Articles

AlN metal–semiconductor field-effect transistors using Si-ion implantation

We report on the electrical characterization of Si-ion implanted AlN layers and the first demonstration of metal–semiconductor field-effect transistors (MESFETs) with an ion-implanted AlN channel. The ion-implanted AlN layers with Si dose of 5 × 1014 cm−2 exhibit n-type characteristics after thermal annealing at 1230 °C. The ion-implanted AlN MESFETs provide good drain current saturation and stable pinch-off operation even at 250 °C. The off-state breakdown voltage is 2370 V for drain-to-gate spacing of 25 µm. These results show the great potential of AlN-channel transistors for high-temperature and high-power applications.

Fabrication and Characteristics of Ion-implanted 4H Silicon Carbide Metal-Semiconductor Field-Effect Transistors on a P-Type Epilayer

The methods for the design and fabrication of ion-implanted 4H silicon carbide (SiC) metal-semiconductor field-effect transistors (MESFETs) have been studied. The N-well regions are formed by three-fold (Sample A) and four-fold (Sample B) nitrogen ionimplantation on Si-face P-type epilayers with a net accept doping concentration of 6.5×10^15 cm^(-3) grown at american corporation Cree. The layout with testing structures has been designed. The locations of the peak concentration and the longitudinal straggles of the implanted ions are simulated by the Monte Carlo simulator TRIM. The box-like profile for the implantation layer is calculated by the Gauss expression. According to the structure of the device and the energy band for the implantation layer, the theoretical equation of the channel depth for the ion-implantation technique is given and calculated. The processes used to determine the implantation energies and doses are discussed. The experiment for ion-implanted 4H-SiC MESFETs is performed. The Ohmic and Schottky contact metals are annealed Ni/Cr alloy and Ti/Pt double-metal layers, respectively, and the pad metallization is Au. The performance of the current-voltage characteristics of the two samples of ion-implanted 4H-SiC MESFETs has been given at the end.

Theoretical investigation of incomplete ionization of dopants in uniform and ion-implanted 4H-SiC MESFETs

The effects of incomplete ionization of nitrogen in 4H-SiC have been investigated. Poisson's equation is numerically analysed by considering the effects of Poole-Frenkel and the effects of the potential on N+d (the concentration of ionized donors) and n (the concentration of electrons). The pinch-off voltages of the uniform and the ion-implanted channels of 4H-SiC metal-semiconductor field-effect transistors (MESFETs) and the capacitance of the gate are given at different temperatures. Both the Poole-Frenkel effect and the potential have influence on the pinch-off voltage Vp of 4H-SiC MESFETs. Although the C-V characteristics of the ion-implanted and the uniform channel of 4H-SiC MESFETs have a clear distinction, the effects of incomplete ionization on the C-V characteristics are not significant.

Current-voltage characteristics of submicrom GaAs MESFETs with nonuniform channel doping profiles

We present a physics-based model for GaAs metal semiconductor field-effect transistors (MESFETs). The present model improves an existing model by allowing the possibility that the electric field near the source region can exceed a critical field, which is likely in an advanced submicrom MESFET operated in the quasi-saturation or saturation region. Furthermore, a realistic and nonuniform channel doping profile was considered in our calculations. Experimental data measured from a low-noise, ion-implanted MESFET are included in support of the model. The effects of different doping profiles and velocity profiles in the channel on the MESFET current-voltage characteristics were also investigated.

UNIFIED GaAs MESFET MODEL FOR CIRCUIT SIMULATIONS

We describe a new, unified model for MEtal Semiconductor Field Effect Transistors (MESFETs) which covers all ranges of operation, including the subthreshold regime. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics are described by continuous, analytical expressions with relatively few, physically based parameters. The model includes effects such as velocity saturation, parasitic series resistances, the dependence of the threshold voltage on drain bias, finite output conductance in saturation, and temperature dependence of the device parameters. We also describe a parameter extraction routine which allows the model parameters to be derived in a straightforward fashion from experimental data. The model has been incorporated into our new circuit simulator AIM-Spice. The new device characterization is applied with good results to a typical ion-implanted GaAs MESFET and a delta-doped MESFET.

Analytical model for I-V characteristics of ion-implanted MESFET's with heavily doped channel

A theoretical model for the I-V characteristics of ion-implanted metal-semiconductor field-effect transistors (MESFETs) has been developed. A formula for effective drift saturation velocity for electrons and a Gaussian approximation for the inverse of reduced distances in the channel have erased the process of formulation. Theoretical formulas for early saturation of drain current and transconductance obtained in the framework of the Lehovec-Zuleeg procedure are quite simple and accurate. When calculated results from the present model are compared with available experimental results, an encouraging correspondence between the two is observed. A study of the appropriateness of the velocity overshoot and the softening of pinch-off voltage indicates that both of these phenomena are real in short-channel MESFETs and need to be carefully accounted for in a realistic model. The model is equally applicable also to ion-implanted JFETs. >

An analytical model for pinchoff voltage evaluation of ion-implanted GaAs MESFETs

The authors describe an analytical model for accurate evaluation of pinchoff voltage and channel thickness of ion-implanted GaAs MESFETs (metal-semiconductor field-effect transistors). A method for calculating I-V characteristics is outlined that uses pinchoff voltage and channel thickness and takes into account the effects of capping, backgating and source and drain resistances. Both single- and multiple-implantation cases are discussed. >

Influence of striations in GaAs on the activated profiles of implanted silicon

Liquid-encapsulated Czochralski-grown GaAs is known to show radial striations. In GaAs:In they can be seen by x-ray topography via fluctuations of the In concentration which cause variations in the lattice constant. Using a high spatial resolution capacitance-voltage technique we investigated In-doped as well as undoped GaAs. It is demonstrated that both materials exhibit striations in the activation behavior of implanted silicon and hence in the threshold voltage of ion-implanted metal-semiconductor field-effect transistors. In the cases investigated here the threshold voltage varied by up to ±12 mV from peak to peak. To our knowledge this is the first time that the effect of striations on the activation behavior of implanted Si is demonstrated in both kinds of substrate material.

Making GaAs integrated circuits

Digital gallium arsenide (GaAs) integrated circuits offer prospects for high-performance electronics, particularly for increased speed and radiation hardness. Prototype GaAs devices fabricated in technologies ranging from ion-implanted metal semiconductor field-effect transistors (MESFETs) and junction field-effect transistors (JFETs) to epitaxial heterostructures, such as high-electron-mobility transistors (HEMTs) and heterojunction bipolar transistors (HBTs), have demonstrated these advantages. While these GaAs technologies share many common fabrication features, the unique characteristics of each and GaAs materials present significant manufacturing challenges. It is argues that to produce real integrated circuits (ICs) for system applications, the disciplines and rigors of a production environment as well as the innovations of research and development are required. >

Neutron radiation effects in GaAs ion-implanted metal-semiconductor field-effect transistors

Neutron radiation investigations have been carried out on ion-implanted GaAs metal-semiconductor field-effect transistors (MESFETs). Device characteristics were measured before irradiation and following neutron irradiations with fluences from 5×1013 to 2×1015 n/cm2. At 5×1013 n/cm2, the device degradation is negligible, while at 2×1015 n/cm2 the threshold voltage shift was 0.7 V and the device transconductance was 30% of its original value. Degradation parameters needed to explain these results are larger than what has been previously reported; this discrepancy is, in part, due to the nonuniform doping profiles in the FET channel. The details of a new model applicable to nonuniform carrier distributions and to density dependent carrier removal rates are presented and results compared to those in the literature. A carrier removal rate of approximately 20 cm−1 is required to explain the degree of observed device degradation.

Integrated quantum-well-laser transmitter compatible with ion-implanted GaAs integrated circuits

The fabrication of an integrated optoelectronic transmitter consisting of an MOCVD-grown quantum-well laser and ion-implanted metal-semiconductor field-effect transistors (MESFETs) is described. The transmitter is characterised by a laser threshold current of 30 mA, differential quantum efficiency of 50%, MESFET transconductance of 60 mS/mm, and operation at frequencies up to 2 GHz.