E. Kohn

InGaP/InGaAs HFET with high current density and high cut-off frequencies

Doped channel pseudomorphic In/sub 0.49/Ga/sub 0.51/P/In/sub 0.20/Ga/sub 0.80/As/GaAs heterostructure field effect transistors have been fabricated on GaAs substrate with 0.25 /spl mu/m T-gates and self-aligned ohmic contact enhancement. By introducing the channel doping and reducing the series resistances, a high current density of 500 mA/mm is obtained in combination with cut off frequencies of f/sub T/=68 GHz and f/sub max/=160 GHz. The channel doping did not affect the RF-performance of the device essentially, which is additionally reflected in noise figures below 1.0 dB with an associated gain of 14.5 dB at 12 GHz.

Electrical characterisation of diamond resistors etched by RIE

Abstract Planar homoepitaxial boron doped diamond films were grown on insulating nitrogen doped synthetic (100) oriented substrates and structured by RIE in Ar O 2 plasma into mesa-resistors. Low etch-rate etching was used to essentially remove the contact influence and profile the active layer by differential etching. Using this technique spike doping profiles in the nm thickness scale can be resolved.

Recess dependent breakdown behavior of GaAs-HFETs

GaAs based HEMT devices were fabricated with a constant recess towards the source, whereas the recess width towards the drain was varied. While the off-state breakdown voltage has been improved by the use of a wide recess towards the drain, no dependence of the on-state breakdown on the recess configuration was observed. The constant breakdown voltage in the on-state is analysed by the feedback parameters obtained from an extraction of the small signal equivalent circuit. Although the extrinsic gate drain capacitance could be reduced by the use of a wider recess configuration, it is assumed that the intrinsic drift region is independent of the recess configuration.<<ETX>>

Dual-gate HFET with closely spaced electrodes on InP

An InGaAs/AlInAs dual-gate HFET with two closely spaced gate electrodes deposited in a common gate recess has been fabricated on InP substrate. The configuration consists of an 0.25 /spl mu/m RF-driven /spl Gamma/-gate overlapping to the source and a DC-trapezoid control gate placed approximately 0.2 /spl mu/m behind the /spl Gamma/-gate. The fabrication sequence allows one to test the device as a single gate FET before deposition of the second gate. The influence of the second gate on the transistor performance was characterized under DC- and RF-conditions. The device current could be fully modulated by either gate and the small signal RF behaviour could be tested in all modes of operation with the second gate RF-grounded. In comparison with the single gate FET, the dual-gate configuration shows an essentially reduced feedback behaviour with reduced C/sub dg/ and G/sub ds/ however, slightly increased input capacitance C/sub gs/. At V/sub ds/=1.2 V f/sub max/ is enhanced by 40%, from 190 GHz to 260 GHz, whereas the gain-bandwidth product decreases from 90 GHz to 70 GHz. The increase of f/sub max/ is strongly drain bias dependent and increases steeply beyond V/sub ds/=1.0 V.

Short-channel effects in 0.5-&#181;m source-drain spaced vertical GaAs FET's&#8212;A first experimental investigation

The output characteristics of vertical GaAs MESFETs with a 0.5 µm source-drain spacing are discussed. It is found that the measured pinch-off voltage is substantially larger than the one expected from the geometrical Schottky diode pinch-off, and current limiting surface depletion effects are not observed.

LT-GaAs with high breakdown strength at low temperature for power MISFET applications

Low temperature grown GaAs has been fabricated containing a limited amount of excess arsenic. The material has a low conductivity in the order of 100KΩ cm, due to hopping in a deep donor band. This σ-LT-GaAs was grown reproducibly by using the lattice mismatch as the primary parameter for substrate temperature calibration. Breakdown fields, in the order of 100kV/cm, are observed for planar structures and increased at low measurement emperatures. Low hopping conductivity and high breakdown field are also observed in the lossy dielectric metal-insulator-semiconductor field-effect transistor device using σ-LT-GaAs as a surface layer. The record radio frequency power density of 4.0W/mm at 77K is extracted from the dc output characteristics.

General diamond Schottky-barrier diode model from locus diagram analysis

Abstract Au Schottky diodes have been fabricated on B-doped natural diamond and analyzed by their frequency-dependent impedance (locus diagram) in the bias and temperature regimes. In comparison with the physical structure, this method allows an equivalent circuit to be established, the individual R and C elements being determined by a network analyzer optimization routine. A three-component circuit configuration is identified.

High field drift domains in GaAs and InP based heterostructure field effect devices

Modelling the high field drift region of HFETs as a drift capacitance between gate and drain in series with the gate capacitance allows one to estimate the extension of the drift region, which determines feedback and output conductance, thus relating the microwave power gain to the device structure. The technique is applied to various GaAs and InP based FET structures.<<ETX>>

Drift region characteristics of InP-based HEMT devices evaluated by a simple drift region model

InP-based HEMTs exhibit superior high frequency performance compared to GaAs PS-HEMTs. This is commonly attributed to a higher electron mobility, saturated velocity and better carrier confinement in the GaInAs QW-channel. Whereas the parameters determining f/sub t/ are well documented, the influence of the carrier confinement and electron dynamics on f/sub max/ is less clear. Intrinsically, a high f/sub max/ relies essentially on the efficiency of the gate-drain high field drift region to separate input and output. Thus, the impact of this region on f/sub max/ has been extensively studied analytically and numerically in the past. Due to the complex electron dynamics involved and the 2D-nature of this region, most models are limited to specific structures and only few general design criteria exist. In this study three structures are compared: an AlInAs/GaInAs HEMT structure on InP is analysed in detail and compared with a GaAs PM-HEMT device and a novel InP-based HEMT structure containing a composite GaInAs-InP QW channel. As mentioned above, the high f/sub max/ of InP-based HEMTs is generally attributed to an improved hot electron confinement. The analysis presented here, however, reveals that the high f/sub max/ of the InP-based devices is mainly linked to an extended lateral drift region and not to an improved carrier confinement.<<ETX>>

Carrier confinement and feed-back correlation in InAlAs/InGaAs HEMTs on InP substrate

The RF behavior of InP-based HEMT structures was evaluated using a feedback correlation. No evidence was found that the deep quantum well InAlAs/InGaAs/InAlAs configuration adds to improved feedback behavior through additional confinement of hot carriers. The model does show that a drift region with a large aspect ratio can develop, which can be traversed by electrons with overshoot velocity leading to high f/sub max//f/sub T/ ratios at high f/sub T/ in the devices. It is concluded that in the design of millimeter-wave InP-based HEMTs, the structural aspect ratio and the aspect ratio of the drift region at the bias region of operation have to be optimized to take maximum advantage of a long drift region combined with a high transit overshoot velocity in the device.<<ETX>>