In-plane Gate Transistors Research Articles

In-plane gates and nanostructures fabricated by direct oxidation of semiconductor heterostructures with an atomic force microscope

The surface of shallow Ga[Al]As heterostructures is locally oxidized with an atomic force microscope. The electron gas underneath the oxide is depleted. We demonstrate experimentally that these depleted regions of the two-dimensional electron gas can be made highly resistive at liquid nitrogen temperatures. Thus, local anodic oxidation of high electron mobility transistors with an atomic force microscope provides a novel method to define nanostructures and in-plane gates. Two examples, namely antidots and quantum point contacts as in-plane gate transistors have been fabricated and their performance at low temperatures is discussed.

Focused ion beam written lateral field-effect transistors on standard silicon wafers

Lateral field effect devices can be produced by focused ion-beam implantation of 100 keV gallium into an arsenic doped layer on standard silicon wafers. The lateral electric field-effect across an implanted line controls the current through a small channel, leading to a gate voltage controlled source-drain current. In-plane gate transistors prepared this way are presented here. With typical geometrical channel widths around 2 μm, they show a drain saturation current of 35 μA and a transconductance of 28 μS. The threshold gallium dose, required to form lateral npn barriers after rapid thermal annealing is about 10 times the carrier density of the n-doped layer. Though the lateral electric field-effect is expected to be sensitive to the sample surface, the unpassivated transistors showed no significant aging over several weeks.

Fabrication and characterisation of SiGe based in-plane-gate transistors

We present an in-situ technology for fabrication of barrier structures in modulation-doped SiSiGe in-plane-gate (IPG) transistors. A special multilayer-resist system is developed for pattern transfer by electron-beam lithography (EBL) and anisotropic SF6O2 dry etching. Barriers are realized by etch-trenches cutting the two dimensional electron gas (2DEG). The trenches are filled up with a low temperature remote plasma enhanced chemical vapour deposition (RPECVD) of silicondioxide (SiO2). Dry-etching and passivation are done in-situ to avoid contamination. IPG transistors with different geometric dimensions have been fabricated and electrically characterised. Transistor operation is demonstrated up to T=77 K. The breakdown voltage and the depletion length of the devices are estimated. The obtained data indicate the advantage of the presented in-situ technology in comparison to other fabrication techniques.

Transport characterization of in-plane gate devices fabricated by direct epitaxial growth on patterned substrates

Direct molecular-beam epitaxial growth of GaAs/AlxGa1−xAs heterostructures on bow-tie shaped constrictions, prepatterned on GaAs substrates is used to fabricate in-plane gate transistors. The fabricated devices can be tuned by applying voltages to in-plane gates, which are also realized during the epitaxial growth. In this way, complete in-plane gate transistors are fabricated in a single growth process. Transport measurements of the devices at 1.3 K show conductance quantization or Coulomb blockade depending on the width of the constriction. The Coulomb blockade effect in the narrowest structures is caused by the formation of a self-assembled quantum dot in the center of the constriction.

In-plane-gate transistors fabricated from Si/SiGe heterostructures by focused ion beam implantation

One-dimensional in-plane-gate (IPG) transistors in the Si/Ge system are fabricated and characterized by focused ion implantation of Ga+ ions on lines into high-mobility two-dimensional electron gases confined in Si/SiGe heterostructures. Transistor operation is demonstrated up to temperatures of T=77 K. The depletion length of the FIB written lines and the saturation drift velocity of the electrons in the Si layer under tensile strain can be estimated from series of samples with different geometric widths of the channel. The IPG transistors presented here are the first based on Si, pushing this elegant transistor concept towards the important Si technology.

Picosecond step-function response of in-plane gate transistor

The high-frequency response of an in-plane gate transistor has been analysed by time-domain transmission measurements using a 20 GHz sampling oscilloscope. Application of a step pulse with 20 ps rise time to the gate of the transistor results in a drain-source current with a rise time of approximately 50 ps. Comparison with the estimated carrier transit time through the channel and with the RC time constant of the device reveals the dominant influence of the parasitic capacitance and the channel resistance on the measured response time.

Ultrafast characterization of an in-plane gate transistor integrated with photoconductive switches

An in-plane gate field-effect transistor is characterized by ultrafast electro-optic sampling. The transistor is monolithically integrated with photoconductive switches in coplanar waveguide and <0.5 ps measurement time resolution is achieved. The gate-drain capacitance of the transistor is obtained as 1.8 fF at zero drain voltage from displacement current transients. The gate-drain capacitance is dominated by parasitic capacitance and the intrinsic gate-drain capacitance is estimated as less than 0.2 fF.

High frequency characteristics of in-plane-gate transistors

Directly written in-plane-gate (IPG) field effect transistors fabricated using focused ion beams have been proposed and measurements of their dc characteristics have been made. Here, we present for the first time ac measurements up to high frequencies on these transistors. The measurements are made using a direct wafer probing technique. While parasitic elements adversely affect the high frequency operation of the current generation of the IPG transistor, promising results have been obtained. We measure a transconductance of 20 μS which is essentially independent of frequency up to 1 GHz.