R. Tauk

Plasma wave detection of terahertz radiation by silicon field effects transistors: Responsivity and noise equivalent power

Si metal oxide semiconductor field effect transistors (MOSFETs) with the gate lengths of 120–300nm have been studied as room temperature plasma wave detectors of 0.7THz electromagnetic radiation. In agreement with the plasma wave detection theory, the response was found to depend on the gate length and the gate bias. The obtained values of responsivity (⩽200V∕W) and noise equivalent power (⩾10−10W∕Hz0.5) demonstrate the potential of Si MOSFETs as sensitive detectors of terahertz radiation.

Ballistic and pocket limitations of mobility in nanometer Si metal-oxide semiconductor field-effect transistors

Room-temperature magnetoresistance of nanometer bulk Si n-type metal-oxide semiconductor field-effect transistors was measured at magnetic fields up to 10 T. The electron magnetoresistance mobility was determined for transistors with the gate length in 30 to 740 nm range and was shown to decrease with decreasing the gate length. We show that the mobility reduction is caused both by the ballistic and the pocket effect and that for the strong inversion these two effects are of a comparable magnitude.

Quasiballistic transport in nanometer Si metal-oxide-semiconductor field-effect transistors : Experimental and Monte Carlo analysis

Room temperature electron mobility (μ) in nanometer Si metal-oxide-semiconductor field-effect transistors (MOSFETs) with gate length (LG) down to 30 nm was determined by the magnetoresistance method. A decrease of μ with the decrease of LG was observed. Monte Carlo simulations of electron transport in nanometer MOSFETs were carried out for realistic devices as a function of LG. The dependence with LG and electron concentration of simulated mobility and transmission coefficient agree with experimental data. An analysis of scattering events and time of flight gives evidence of the presence of ballistic motion in the investigated structures and proves its influence on mobility degradation in short transistors. The results give arguments that interpretation of the magnetoresistance coefficient as the square of the mobility is valid also in the case of quasiballistic electron transport.

Blue (Ga,In)N/GaN Light Emitting Diodes on Si(110) Substrate

We have fabricated and characterized blue (Ga,In)N/GaN multiple quantum well light emitting diodes grown on a Si(110) substrate by molecular beam epitaxy. For a 20 mA current, we have found that the operating voltage and the series resistance are as low as 3.5 V and 17 Ω, respectively. A maximum light output power of 72 µW is obtained as measured on the wafer. These characteristics are almost identical to those obtained on a reference sample grown on the commonly used Si(111) orientation.

Quantum and transport lifetimes of two-dimensional electrons gas in AlGaN/GaN heterostructures

The transport and quantum lifetimes were respectively deduced from low-temperature mobility and Shubnikov–de Haas measurements as a function of carrier density in metal organic vapor phase epitaxy-grown AlGaN∕GaN∕sapphire heterostructures. We show experimentally that the lifetime ratio varies as a bell curve, qualitatively confirming a recent theoretical prediction. However the experimental ratio varied much less than was theoretically predicted: From 9 to 19 for carrier densities in 1–9×1012cm−2 range. Moreover, we show the variation of quantum time with carrier density presents some discrepancy with the theoretical study. We also show that transport to quantum lifetime ratio cannot be used alone as a clear figure of merit from AlGaN∕GaN heterojunctions.

Low electron mobility of field-effect transistor determined by modulated magnetoresistance

Room temperature magnetotransport experiments were carried out on field-effect transistors in magnetic fields up to 10 T. It is shown that measurements of the transistor magnetoresistance and its first derivative with respect to the gate voltage allow the derivation of the electron mobility in the gated part of the transistor channel, while the access/contact resistances and the transistor gate length need not be known. We demonstrate the potential of this method using GaN and Si field-effect transistors and discuss its importance for mobility measurements in transistors with nanometer gate length.

Low temperature electron mobility and concentration under the gate of AlGaN/GaN field effect transistors

High electron mobility field effect transistors were fabricated on AlGaN∕GaN heterostructures and their magnetoresistance was measured at 4.2K up to 10T with simultaneous modulation of the gate potential. Low and high magnetic field data were used to determine the electron mobility (μ) and concentration (n), respectively, in the gated part of the transistor channel. With these measurements we present a method to determine μ and n under the gate of a transistor, which does not require knowledge of the transistor gate length, access resistance, threshold voltage, or capacitance. We discuss applications of this method for nanometer and ballistic transistors.

Measurement of the effect of plasmon gas oscillation on the dielectric properties of p- and n-doped AlxGa1−xN films using infrared spectroscopy

We report on the application of infrared (IR) spectroscopy as an approach to nondestructive optical method for quantitative measurement of relevant optoelectronic properties in complex multilayer systems. We developed a numerical technique to analyze quantitatively the dielectric properties and plasmon gas characteristics from infrared reflectivity measurements. The developed technique is based on the combination of Kramers-Kronig theorem with the classical theory of electromagnetic wave propagation in a system of thin films. We applied the approach to deduce the dielectric properties and plasmon gas characteristics in p- and n-doped AlGaN alloys of various compositions, deposited on AlN(100 nm)/GaN(30 nm)/Al2O3. The results agreed with the electrical measurements, and the back calculation reproduced satisfactory the reflectivity measurements, demonstrating the accuracy of the developed technique.

Synthesis and characterization of a photosensitive organic–inorganic, hybrid positive resin type material: application to the manufacture of microfluidic devices by laser writing

A positive working and chemical amplified photosensitive organic–inorganic hybrid material based on PAA polymer with a lower molecular weight, 1,3,5-tris[(2-vinyloxy)ethoxy]benzene (TVEB) as a crosslinking dissolution inhibitor, a VEPTES pre-hydrolysed as an organic–inorganic material and a PAG photoacid generator was developed. The TVEB was prepared by coupling 1,3,5-trihydroxybenzene and 2-chloroethyl vinyl ether. The hybrid photosensitive material showed sensitivity when exposed to UV light at 375 nm followed by development with a 2.38 wt% aqueous solution of TMAH at room temperature. The synthesis of the material was followed by FTIR spectroscopy to follow the crosslinking of the vinyl ether group from TVEB and VEPTES with the carboxylic group of the PAA polymer.

Design and controlled synthesis by dual polymerization of new organic–inorganic hybrid material for photonic devices

Organic–inorganic hybrid material was synthesized by double polymerization processes i.e. a sol–gel process and organic polymerization respectively. For this study, hybrid monomer, 4-vinyl ether-phenyltriethoxysilane (VEPTES) was used as starting building block. First, the silica matrix with tunable ratio of siloxane and silanol units was synthesized by a sol–gel process under acidic conditions and the organic network was formed by cationic photopolymerization of vinyl ether groups. Mineral and organic polymerization kinetics were respectively monitored by liquid 29Si-NMR and IR spectroscopy. The effect of the silicate backbone on the organic photopolymerization process was studied and elucidated. The optical performance of this new hybrid material has been studied using the near-infrared spectroscopy.