Quantum-wire Field-effect Transistors Research Articles

Influence of Band Non-Parabolicity on Few Ballistic Properties of III–V Quantum Wire Field Effect Transistors Under Strong Inversion

A simplified yet analytical approach on few ballistic properties of III-V quantum wire transistor has been presented by considering the band non-parabolicity of the electrons in accordance with Kane's energy band model using the Bohr-Sommerfeld's technique. The confinement of the electrons in the vertical and lateral directions are modeled by an infinite triangular and square well potentials respectively, giving rise to a two dimensional electron confinement. It has been shown that the quantum gate capacitance, the drain currents and the channel conductance in such systems are oscillatory functions of the applied gate and drain voltages at the strong inversion regime. The formation of subbands due to the electrical and structural quantization leads to the discreetness in the characteristics of such 1D ballistic transistors. A comparison has also been sought out between the self-consistent solution of the Poisson's-Schrodinger's equations using numerical techniques and analytical results using Bohr-Sommerfeld's method. The results as derived in this paper for all the energy band models gets simplified to the well known results under certain limiting conditions which forms the mathematical compatibility of our generalized theoretical formalism.

Temperature-dependent conductance of quasi-one-dimensional electrons in a novel constricted [formula omitted] channel with corrugated interfaces

Transport properties of a novel quasi-ballistic quantum wire field-effect transistor are studied experimentally and then discussed in relation to a theory for dirty Tomonaga–Luttinger (T–L) liquids. The sample was prepared by constricting lithographically an epitaxially grown In 0.1 Ga 0.9 As / GaAs quantum well channel, whose bottom interface is corrugated by a quasi-periodic array of multi-atomic steps of 20 nm in periodicity. A quasi-one-dimensional channel of about 200 nm in metallurgical width and 2 μ m in length was formed and its conductance parallel to the steps was measured at temperatures between 4 and 0.3 K as a function of gate voltage. Plateau-like structures substantially lower than 2 e 2 / h were observed. The conductance at each gate voltage decreases sensitively as temperature lowers until it gets nearly constant below a critical temperature. These tendencies are found to be qualitatively consistent with the theory of Ogata and Fukuyama for dirty T–L liquids. The temperature dependence above the critical temperature is found to fit quantitatively with the formula of Ogata and Fukuyama, if the parameters are suitably chosen.

Negative differential resistance of pseudomorphic InGaAs quantum-wire FETs

Pseudomorphic trench-type InGaAs/InAlAs quantum-wire field-effect transistors (QWR-FETs) are realized on (3 1 1)A InP V-groove substrates by selective molecular beam epitaxy. Negative differential resistance (NDR) spectra are clearly observed in the 50–240 K temperature range for the In 0.7Ga 0.3As QWR-FET, and up to 260 K for the In 0.8Ga 0.2As QWR-FET. These temperature ranges are higher than that of a lattice-matched QWR-FET, and this is thought to be due to the higher electron mobility in the pseudomorphic QWR layer. The NDR temperature range increases as the QWR In content increases and the FET gate length decreases.

Enhanced peak-to-valley current ratio in InGaAs∕InAlAs trench-type quantum-wire negative differential resistance field-effect transistors

Trench-type narrow InGaAs quantum-wire field-effect transistors (QWR-FETs) have been fabricated on (311)A InP V-groove substrates by hydrogen-assisted molecular-beam epitaxy. Enhanced negative differential resistance (NDR) effects with a peak-to-valley ratio (PVR) as high as 13.3 have been observed at an onset voltage of 0.16V in the QWR-FETs at 24K. The PVR increased with reductions in the InGaAs epitaxial layer thickness, which caused an enhanced mobility difference between the QWR and side quantum wells (QWs). This forms a velocity modulation transistor based on the real-space transfer of electrons from the high mobility QWR to the low mobility side QWs. The NDR effects were observed up to 230K as the gate length was decreased to 50nm. A unique feature of the QWR-FET is that NDR effects are controllable with the gate bias in a three-terminal configuration.

Photoconductive characteristics in a trench-type InGaAs quantum-wire field effect transistor

We describe the photoconductive characteristics of a narrow trench-type InGaAs quantum wire field effect transistor (QWR-FET) with a negative differential resistance (NDR). The photoconductive intensity peak of the trench-type QWR was observed at a drain voltage (VDS) region lower than an onset voltage of NDR (VNDR), and decreased at the VDS larger than the VNDR. This result indicates that the carriers transfer from the QWR level to other quantum levels at the VDS region larger than the VNDR. By numerically solving the two-dimensional single band Schrödinger equation using the finite element method, we confirm that the carrier can transfer from the high mobility QWR layer to the low mobility sidewall quantum wells, which is thought to be a mechanism of the negative differential resistance of the QWR-FETs.

Pseudomorphic InGaAs quantum-wire FETs with negative differential resistance

Pseudomorphic trench-type InGaAs/InAlAs quantum-wire field-effect transistors (QWR-FET) are realized by selective molecular beam epitaxy. The pseudomorphic QWR-FET has a negative differential resistance (NDR) effect with a low source–drain voltage (0.3 V). The NDR spectra are clearly observed in the 50–220 K temperature range. The operating current of the pseudomorphic QWR-FET is twice that of a lattice-matched QWR-FET, and this is thought to be due to the higher electron mobility.

Negative differential resistance effects of trench-type InGaAs quantum-wire field-effect transistors with 50-nm gate-length

The effects of negative differential resistance (NDR) have been clearly observed in 50-nm-gate InGaAs/InAlAs trench-type quantum-wire (QWR) field-effect transistors (FETs), which are fabricated by atomic hydrogen-assisted molecular-beam epitaxy. The NDR onset voltage is as low as 0.1 V, and the highest peak-to-valley current ratio is 6.2 at 40 K. The equilateral symmetry of the NDR effect in a QWR FET is also observed. The pronounced NDR effects in a trench-type QWR FET are advantageous for high-speed and low power-consumption devices.

Magneto-conductance fluctuations in a V-grooved GaAs quantum-wire

We study the magneto-resistance of a V-grooved GaAs quantum-wire field-effect transistor (QWR-FET) realized by selective growth of metalorganic vapor phase epitaxy. At low temperatures, the magneto-resistance of the wire shows reproducible fluctuations resulting from the quantum interference of electrons in the wire. The gate-voltage and temperature dependence of the conductance fluctuations are studied, and the latter reveal evidence for the robust phase coherence of electrons in the V-grooved QWR.

V-grooved InGaAs quantum-wire FET fabricated under an As2 flux in molecular-beam epitaxy

Abstract V-grooved InGaAs/InAlAs quantum-wire field-effect transistors are realized by selective molecular-beam epitaxy and their transport characteristics are studied. The QWR structures are formed using a combination of atomic hydrogen and a dimer arsenic source. An analysis of the depopulation of one-dimensional sub-bands in these structures reveals little evidence for sidewall depletion. Sub-band splittings as large as 6.6 meV are obtained in the wires, indicating their excellent one-dimensional transport properties.

Trench-type InGaAs quantum-wire field effect transistor with negative differential conductance fabricated by hydrogen-assisted molecular beam epitaxy

Trench-type narrow InGaAs quantum wires (QWRs) with a cross-sectional depth of 8 nm and a width of 25 nm have been successfully fabricated by hydrogen-assisted molecular beam epitaxy. Optical properties of the QWRs are improved by atomic-hydrogen irradiation as observed by photoluminescence measurement. The trench-type QWR-FET has a pronounced negative differential conductance with a low onset voltage and a high peak-to-valley current ratio. We also study the quantum-interference characteristics of the trench-type QWR-FET, and find very different behavior to that typically exhibited by disordered wires. This Aharonov–Bohm effect points to an interference process in which the one-dimensional subbands of the wire themselves constitute well-resolved paths for electron interference.

Quantum-interference characteristics of a 25 nm trench-type InGaAs/InAlAs quantum-wire field-effect transistor

We study the quantum-interference characteristics of a 25 nm, trench-type, InGaAs quantum-wire field-effect transistor realized by selective epitaxy, and find very different behavior from that typically exhibited by disordered wires. The amplitude of the magnetoresistance fluctuations is exponentially suppressed at high fields, where evidence of an Aharonov–Bohm effect is observed. The exponential suppression appears to be consistent with theoretical predictions for the influence of magnetic field on the scattering rate in clean wires, while the Aharonov–Bohm effect points to an interference process in which the one-dimensional subbands of the wire themselves constitute well-resolved paths for electron interference.

Quasi-one-dimensional transport characteristics of ridge-type InGaAs quantum-wire field-effect transistors

Ridge-type InGaAs/InAlAs quantum-wire field-effect transistors are realized by selective molecular-beam epitaxy and their transport characteristics are studied. An analysis of the depopulation of one-dimensional subbands in these structures reveals little evidence for sidewall depletion, and yields an estimate for the carrier density in good agreement with that found in two-dimensional InGaAs/InAlAs heterojunctions. Subband splittings as large as 7.4 meV are obtained in the wires, indicating their excellent one-dimensional transport properties.

Gate-length dependence of negative differential resistance in ridge-type InGaAs/InAlAs quantum wire field-effect transistor

We investigate the gate-length dependence of negative differential resistance (NDR) in a ridge-type InGaAs/InAlAs quantum wire field-effect transistor with a gate varying from 50 nm to 1 μm in length. The gate leakage current is detectable only with the onset of NDR and increases with larger gate bias. The NDR could be attributed to the real space transfer of channel carrier into the barrier layer by gate field-assisted tunneling. The NDR characteristics are dependent strongly on gate length. The improvement in NDR characteristic in terms of peak-to-valley current ratio and onset voltage (VNDR) is observed clearly with the reduction of gate length. The QWIR-FETs with shorter gate length show the NDR even at room temperature. The improvement in NDR characteristic is attributed to a velocity overshoot enhanced by the suppression of scattering probability.

Self-organized (553)BIn0.15Ga0.85As/GaAs quantum-wire field-effect transistors

Extremely uniform and high-density In0.15Ga0.85As/GaAs quantum wires (QWRs) were naturally formed on a (553)B-oriented GaAs substrate by molecular-beam epitaxy. The density of the QWRs is as high as 4.0×105 cm−1. The strong photoluminescence peak at λ=868 nm from the (553)B QWRs shows a large polarization anisotropy [p=(I∥−I⊥)/(I∥+I⊥)=0.22] and a very small full width at half maximum of 9.2 meV at 12 K. Based on the modulation-doped (553)B QWR structure, self-organized QWR field-effect transistors were fabricated (the channel along the QWRs’ direction). The devices demonstrate very good saturation characteristics and pinch-off behavior at room temperature. A maximum transconductance (gm) of 135 mS/mm is measured for 2 μm gate-length devices.

Observation of negative differential resistance of a trench-type narrow InGaAs quantum-wire field-effect transistor on a (311)A InP substrate

A trench-type narrow InGaAs quantum-wire field-effect transistor (QWR–FET) with a cross section of 8×25 nm has been fabricated on a (311)A InP V-grooved substrate by molecular-beam epitaxy. The trench-type InGaAs QWR–FET has normal static characteristics at room temperature, and demonstrates clear negative differential resistance characteristics at 40 K with a high peak-to-valley current ratio (PVR=4.3) and a low onset voltage of 0.12 V.

Negative differential resistance of a ridge-type InGaAs quantum wire field-effect transistor

Negative differential resistance with a high peak to valley ratio and low onset voltage is clearly observed in a quantum wire field-effect transistor (QWR-FET) with a channel width of 100 nm, while it is not observed in a QWR-FET with a channel width of 300 nm. The saturation characteristics of Landau plots indicate that the 100 nm wide QWR has one-dimensional characteristics of electron transport, as opposed to the 300 nm wide QWR that has two-dimensional electrons.

Large and anisotropic zero-field spin-splittings in InxGa1−xAs/InyAl1−yAs (x,y>0.6) heterojunctions

Large and in-plane anisotropic zero-field spin-splittings are found in two-dimensional electron gas (2DEG) formed at InxGa1−xAs/InyAl1−yAs (x,y>0.6) heterojunctions. Low-temperature magnetoresistance (MR) measurements were carried out in van der Pauw, Hall bar and quantum wire field effect transistor (QWR-FET) samples. Maximum spin–orbit coupling constant αzero of 78(×10−12eVm) was attained at 1.5 K in the Hall bar sample with the 〈−110〉 direction. Also, an in-plane anisotropy of almost twice as well as a gate-voltage-dependent change of αzero are confirmed in QWR-FET samples with 〈−110〉 and 〈110〉 directions. Those results suggest the importance of interface contribution to the zero-field spin splitting, which might be enhanced in our unique heterojunctions.

Possible large zero-field spin-splittings in In xGa 1− xAs/In yA1 1− yAs ( x, y=0.75) heterojunctions

Zero-field spin-splittings are estimated from low-temperature magnetoresistances in two-dimensional electron gas (2DEG) in In x Ga 1−x As/ In y A1 1−y As (x,y=0.75) van der Pauw, Hall-bar and quantum wire field effect transistor (QWR-FET) samples. Maximum spin–orbit coupling constant α zero of 78 (×10 −12 eVm) was obtained in the Hall bar sample with 〈−1 1 0〉 direction, which has a sheet electron density and a mobility at 1.5 K of 1.1×10 12/cm 2 and 5.54×10 5 cm 2/ Vs . In-plane anisotropies of mobility as well as of α zero are confirmed in QWR-FET samples with 〈1 1 0〉 and 〈1 1 0〉 directions. If those results are considered together with the fact that a part of α zero was able to be changed by the gate-voltage, interface effect contributing to the zero-field splitting might play an important role in this heterojunction.

Observation of N-shaped negative differential resistance in ridge-type InGaAs/InAlAs quantum wire field-effect transistor

N-shaped negative differential resistance (NDR) with high peak-to-valley ratio (PVR) and low onset voltage ( V NDR) are clearly observed in a 50-nm gate ridge-type InGaAs/InAlAs quantum wire field-effect transistor (QWR-FET). The NDR of low onset voltage ( V NDR) and its dependence on the gate voltage are attributed to the real space transfer of channel carriers into a barrier layer underneath the gate by field-assisted tunneling. The NDR characteristic of the QWR-FET is enhanced compared with that of InGaAs/InAlAs quantum well field-effect transistor (QW-FET). The narrower channel width and shorter gate length effectively improve the PVR and V NDR.

Spin-splitting transport in In 0.75Ga 0.25As/In 0.75Al 0.25As quantum wire field-effect-transistor

We have made quantum wire field-effect-transistor (QWR-FET) in normal-type In 0.75Ga 0.25As/In 0.75Al 0.25As modulation-doped heterostructure and investigated spin-splitting properties by low-temperature magnetoresistance (MR) measurements. Maximum value of zero-field spin–orbit coupling constant, α zero, obtained here is 78 (×10 −12 eVm). We also confirmed an in-plane anisotropy of α zero, that is, different α zeros in between 〈 1 ̄ 1 0〉 and 〈1 1 0〉 directed samples and a reduction of α zero by applying negative gate biases. In MR measurements, we also observed conductance fluctuations superimposing on the beat oscillation in the sample with widths less than 2 μm.