Field-effect Transistor Heterostructures Research Articles

Quantitative Determination on Ionic-Liquid-Gating Control of Interfacial Magnetism.

Ionic-liquid gating on a functional thin film with a low voltage has drawn a lot of attention due to rich chemical, electronic, and magnetic phenomena at the interface. Here, a key challenge in quantitative determination of voltage-controlled magnetic anisotropy (VCMA) in Au/[DEME]+ [TFSI]- /Co field-effect transistor heterostructures is addressed. The magnetic anisotropy change as response to the gating voltage is precisely detected by in situ electron spin resonance measurements. A reversible change of magnetic anisotropy up to 219 Oe is achieved with a low gating voltage of 1.5 V at room temperature, corresponding to a record high VCMA coefficient of ≈146 Oe V-1 . Two gating effects, the electrostatic doping and electrochemical reaction, are distinguished at various gating voltage regions, as confirmed by X-ray photoelectron spectroscopy and atomic force microscopy experiments. This work shows a unique ionic-liquid-gating system for strong interfacial magnetoelectric coupling with many practical advantages, paving the way toward ion-liquid-gating spintronic/electronic devices.

Defect assistant band alignment transition from staggered to broken gap in mixed As/Sb tunnel field effect transistor heterostructure

The compositional dependence of effective tunneling barrier height (Ebeff) and defect assisted band alignment transition from staggered gap to broken gap in GaAsSb/InGaAs n-channel tunnel field effect transistor (TFET) structures were demonstrated by x-ray photoelectron spectroscopy (XPS). High-resolution x-ray diffraction measurements revealed that the active layers are internally lattice matched. The evolution of defect properties was evaluated using cross-sectional transmission electron microscopy. The defect density at the source/channel heterointerface was controlled by changing the interface properties during growth. By increasing indium (In) and antimony (Sb) alloy compositions from 65% to 70% in InxGa1−xAs and 60% to 65% in GaAs1−ySby layers, the Ebeff was reduced from 0.30 eV to 0.21 eV, respectively, with the low defect density at the source/channel heterointerface. The transfer characteristics of the fabricated TFET device with an Ebeff of 0.21 eV show 2× improvement in ON-state current compared to the device with Ebeff of 0.30 eV. On contrary, the value of Ebeff was decreased from 0.21 eV to −0.03 eV due to the presence of high defect density at the GaAs0.35Sb0.65/In0.7Ga0.3As heterointerface. As a result, the band alignment was converted from staggered gap to broken gap, which leads to 4 orders of magnitude increase in OFF-state leakage current. Therefore, a high quality source/channel interface with a properly selected Ebeff and well maintained low defect density is necessary to obtain both high ON-state current and low OFF-state leakage in a mixed As/Sb TFET structure for high-performance and lower-power logic applications.

High electron mobility lattice-matched AlInN∕GaN field-effect transistor heterostructures

Room temperature electron mobility of 1170cm2∕Vs is obtained in an undoped, lattice-matched, Al0.82In0.18N∕GaN field-effect transistor heterostructure, while keeping a high (2.6±0.3)×1013cm−2 electron gas density intrinsic to the Al0.82In0.18N∕GaN material system. This results in a two-dimensional sheet resistance of 210Ω∕◻. The high mobility of these layers, grown by metal-organic vapor phase epitaxy on sapphire substrate, is obtained thanks to the insertion of an optimized AlN interlayer, reducing the alloy related interface roughness scattering.

Monolithically integrated bacteriorhodopsin–GaAs field-effect transistor photoreceiver

We have applied the large photovoltage developed across a layer of selectively deposited bacteriorhodopsin to the gate terminal of a monolithically integrated GaAs-based modulation-doped field-effect transistor, which delivers an amplified photoinduced current signal. The integrated biophotoreceiver device exhibits a responsivity of 3.8 A/W. The optoelectronic integrated circuit is achieved by molecular-beam epitaxy of the field-effect transistor's heterostructure, photolithography, and selective-area bacteriorhodopsin electrodeposition.

Electron effective mass determination in asymmetric modulation-doped field-effect transistor heterostructures using InxGa1 − xAs quantum well and InAs–GaAs superlattice channels

Cyclotron resonance and photoluminescence measurements have been performed on two types of modulation-doped field-effect transistor heterostructures having their bidimensional channel based, respectively, on an InxGa1−xAs quantum well and an InAs–GaAs short-period superlattice. A linear dependence of the electron effective mass as a function of indium content of the channel was obtained from cyclotron resonance measurements. For a given average value of the indium content, the effective mass in the InAs–GaAs short-period superlattice channel is found to be systematically higher than that obtained in structures with an alloy-based channel. This is attributed to larger nonparabolic effects in the former case. In our theoretical model, the electron and heavy hole energy levels and the electron wavefunction are determined self-consistently and used to estimate the nonparabolic corrections that apply to the effective mass deduced from cyclotron resonance measurements.

Study of Hall and effective mobilities in pseudomorphic Si1−xGex p-channel metal–oxide–semiconductor field-effect transistors at room temperature and 4.2 K

A study of several Si0.8Ge0.2 p-channel heterostructures with self-aligned poly-Si metal–oxide–semiconductor gates were carried out. A novel fabrication process was developed which is compatible with the strained Si/SiGe system, and it has allowed Hall and resistivity measurements to be performed at room temperature and at 4.2 K. The structures were numerically modelled to calculate the charge distribution with temperature and with gate voltage and the results have shown good agreement with experiment. Hall measurements at 4.2 K have shown consistent SiGe channel Hall mobility enhancements of ×3 over the SiO2/Si channels in the same devices. Room temperature effective mobilities were measured for a buried Si0.8Ge0.2 p-channel metal–oxide–semiconductor field-effect transistor heterostructure using capacitance–voltage measurements to calculate the carrier density. Mobilities are consistently over 300 cm2/V s and the low temperature studies, together with measurements of comparable modulation doped heterostructures, and secondary-ion-mass spectroscopy depth profiles suggest that this mobility is at present limited by the quality and proximity of the SiO2/Si interface.

Cyclotron resonance in asymmetric modulation-doped field-effect transistor heterostructures using In[sub x]Ga[sub 1−x]As quantum well and InAs–GaAs superlattice channels

Cyclotron resonance and photoluminescence measurements were carried out on two types of modulation-doped field-effect transistor heterostructures whose channels were made of an InAs–GaAs short-period superlattice and of an InxGa1−xAs quantum well, respectively. From cyclotron resonance data a linear dependence of the channel electron effective mass on indium content was obtained for both series of samples. For a given mean value of the indium content in the channel, the effective mass is found to be systematically higher in samples where the channel is based on a short-period superlattice rather than on an alloy-based channel. This can be attributed to larger nonparabolic effects in the former. Calculations of nonparabolicity corrections are in agreement with these results. In our theoretical model, the energy of the electron and heavy hole levels were determined self-consistently.

Extrinsic layer at AlxGa1−xAs-GaAs interfaces

Photoluminescence studies of GaAs-AlxGa1−xAs heterostructures grown by molecular beam epitaxy (MBE) which contain one and two GaAs quantum wells suggest that in some of the samples the first well grown usually exhibits a ’’rough’’ (6 Å≲δL≲15 Å) first interface and an acceptorlike luminescing impurity in the first few tens of angstroms of GaAs grown. The luminescence may arise from carbon which accumulates on the AlxGa1−xAs -vacuum interface during growth and is then deposited in the first few unit cells of GaAs. The phenomenon discussed may be relevant to the problem of growing high electron mobility field-effect transistor heterostructures by MBE with GaAs on the top.