Copper phthalocyanine based hybrid p-type permeable-base transistor in vertical architecture

We demonstrate the production of copper phthalocyanine (CuPc) based p-type hybrid permeable-base transistors, which operate at low voltages having high common-base current gains. These transistors are prepared by evaporating a thin metal layer (Ag or Al) that acts as base on top of a Si substrate that acts as collector. In the sequence CuPc and Au are thermally sublimated to produce the emitter, constituting a quite simple device production procedure with the additional advantage of allowing higher integration due to its vertical architecture.

High current density tris(8-hydroxyquinoline) aluminum-based hybrid transistor in vertical architecture

We report the construction of hybrid permeable-base transistors, in vertical architecture, using tris(8-hydroxyquinoline) aluminum as emitter, a thin gold layer as base, and n-type silicon as collector. These transistors present high common-base current gain, can be operated at low driving voltages, and allow high current density.

Synthesis of MDMO-PPV capped PbS quantum dots and their application to solar cells

Poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) capped PbS quantum dots about 3-6 nm in diameter were synthesized with a novel method. Unlike the synthesis of oleic acid capped PbS quantum dots, the reactions were carried out in solution at room temperature, with the presence of a capping ligand species, MDMO-PPV. The quantum dots were used to fabricate bulk heterojunction solar cells with an indium tin oxide (ITO)/polyethylenedioxythiophene/polystyrenesulphonate (PEDOT: PSS)/MDMO-PPV: PbS/Al structure. Current density-voltage characterization of the devices showed that after the addition of the MDMO-PPV capped PbS quantum dots to MDMO-PPV film, the performance was dramatically improved compared with pristine MDMO-PPV solar cells. (C) 2008 Elsevier Ltd. All rights reserved.

Growth and fabrication of AlGaN/GaN HEMT based on Si(111) substrates by MOCVD

AlGaN/GaN high electron mobility transistor (HEMT) hetero-structures were grown on the 2-in Si (1 1 1) substrate using metal-organic chemical vapor deposition (MOCVD). Low-temperature (LT) AlN layers were inserted to relieve the tension stress during the growth of GaN epilayers. The grown AlGaN/GaN HEMT samples exhibited a maximum crack-free area of 8 mm x 5 mm, XRD GaN (0 0 0 2) full-width at half-maximum (FWHM) of 661 arcsec and surface roughness of 0.377 nm. The device with a gate length of 1.4 mu m and a gate width of 60 mu m demonstrated maximum drain current density of 304 mA/mm, transconductance of 124 mS/mm and reverse gate leakage current of 0.76 mu A/mm at the gate voltage of -10 V. (C) 2008 Published by Elsevier Ltd.

Effect of CO on characteristics of AlGaN/GaN Schottky diode

Pt Schottky diode gas sensors for CO are fabricated using AlGaN/ GaN high electron mobility transistor ( HEMTs) structure. The diodes show a remarkable sensor signal (3 mA, in N-2; 2mA in air ambient) biased 2V after 1% CO is introduced at 50 degrees C. The Schottky barrier heights decrease for 36meV and 27meV in the two cases respectively. The devices exhibit a slow recovery characteristic in air ambient but almost none in the background of pure N2, which reveals that oxygen molecules could accelerate the desorption of CO and offer restrictions to CO detection.

Multiple valley couplings in nanometer Si metal-oxide-semiconductor field-effect transistors

We investigate the couplings between different energy band valleys in a metal-oxide-semiconductor field-effect transistor (MOSFET) device using self-consistent calculations of million-atom Schrodinger-Poisson equations. Atomistic empirical pseudopotentials are used to describe the device Hamiltonian and the underlying bulk band structure. The MOSFET device is under nonequilibrium condition with a source-drain bias up to 2 V and a gate potential close to the threshold potential. We find that all the intervalley couplings are small, with the coupling constants less than 3 meV. As a result, the system eigenstates derived from different bulk valleys can be calculated separately. This will significantly reduce the simulation time because the diagonalization of the Hamiltonian matrix scales as the third power of the total number of basis functions. (C) 2008 American Institute of Physics.

High performance 1689-nm quantum well diode lasers

1689-nm diode lasers used in medical apparatus have been fabricated and characterized. The lasers had pnpn InP current confinement structure, and the active region consisted of 5 pairs of InGaAs quantum wells and InGaAsP barriers. Stripe width and cavity length of the laser were 1.8 and 300 pm, respectively. After being cavity coated. and transistor outline (TO) packaged, the lasers showed high performance in practice. The threshold current was about 13 +/- 4 mA, the operation current and the lasing spectrum were about 58 6 mA and 1689 +/- 6 nm at 6-mW output power, respectively. Moreover, the maximum output power of the lasers was above 20 mW.

An ultra-low power CMOS random number generator

This paper proposes an ultra-low power CMOS random number generator (RING), which is based on an oscillator-sampling architecture. The noisy oscillator consists of a dual-drain MOS transistor, a noise generator and a voltage control oscillator. The dual-drain MOS transistor can bring extra-noise to the drain current or the output voltage so that the jitter of the oscillator is much larger than the normal oscillator. The frequency division ratio of the high-frequency sampling oscillator and the noisy oscillator is small. The RNG has been fabricated in a 0.35 mu m CMOS process. It can produce good quality bit streams without any post-processing. The bit rate of this RNG could be as high as 100 kbps. It has a typical ultra-low power dissipation of 0.91 mu W. This novel circuit is a promising unit for low power system and communication applications. (c) 2007 Elsevier Ltd. All rights reserved.

Hydrogen sensors based on AlGaN/AIN/GaN HEMT

Pt/AlGaN/AIN/GaN high electron mobility transistors (HEMT) were fabricated and characterized for hydrogen sensing. Pt and Ti/Al/Ni/Au metals were evaporated to form the Schottky contact and the ohmic contact, respectively. The sensors can be operated in either the field effect transistor (FET) mode or the Schottky diode mode. Current changes and time dependence of the sensors under the FET and diode modes were compared. When the sensor was operated in the FET mode, the sensor can have larger current change of 8 mA, but its sensitivity is only about 0.2. In the diode mode, the current change was very small under the reverse bias but it increased greatly and gradually saturated at 0.8 mA under the forward bias. The sensor had much higher sensitivity when operated in the diode mode than in the FET mode. The oxygen in the air could accelerate the desorption of the hydrogen and the recovery of the sensor. (c) 2007 Elsevier Ltd. All rights reserved.

A new phototransistor with uni-travelling-carrier and optically gradual coupling properties

Based on appropriate combination of different band-gap InGaAsP, a new edge-coupled two-terminal double heterojunction phototransistor (ECTT-DHPT) was designed and fabricated, which is double heterojunction, free-aluminium, and works under uni-travelling-carrier mode and optically gradual coupling mode. This device is fully compatible with monolithic micro-wave integrated circuits (MMIC) and heterojunction bipolar transistor (HBT) in material and process. The DC characteristics reveal that the new ECTT-DHPT can perform good optoelectronic mix operation and linear amplification operation by optically biased at two appropriate value respectively. Responsivity of more than 52 A/W and dark current of 70 nA (when V-EC = 1 V) were obtained.

Reduced dynamics with renormalization in solid-state charge qubit measurement

Quantum measurement will inevitably cause backaction on the measured system, resulting in the well-known dephasing and relaxation. In this paper, in the context of solid-state qubit measurement by a mesoscopic detector, we show that an alternative backaction known as renormalization is important under some circumstances. This effect is largely overlooked in the theory of quantum measurement.

The application of SnS nanoparticles to bulk heterojunction solar cells

Tin mono-sulphide (SnS) nanoparticles were synthesized by a facile method. Reactions producing narrow size distribution SnS nanoparticles with the diameter of 5.0-10 nm were carried out in an ethylene glycol solution at 150 degrees C for 24 h. Bulk heterojunction solar cells with the structure of indium tin oxide (ITO)/polyethylenedioxythiophene polystyrenesulphonate (PEDOT PSS)/SnS polymer/Al were fabricated by blending the nanoparticles with a conjugated polymer to form the active layer for the first time. Current density-voltage characterization of the devices showed that due to the addition of SnS nanoparticles to the polymer film, the device performance can be dramatically improved, compared with that of the pristine polymer solar cells. (c) 2009 Published by Elsevier B.V.

The synthesis of MDMO-PPV capped PbS nanorods and their application in solar cells

Poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) capped PbS nanorods about 100 nm in diameter and 400 nm in length were synthesized via a hydrothermal route in toluene and dimethylsulfoxide solution. By blending the PbS nanorods with the MDMO-PPV as the active layer, bulk heterojunction solar cells with an indium tin oxide (ITO)/polyethylenedioxythiophene/polystyrenesulphonate (PEDOT PSS)/MDMO-PPV PbS nanorods/Al structure were fabricated in a N-2 filled glove box, Current density-voltage characterization of the devices showed that the solar cells with PbS nanorods hybrid with MDMO-PPV as active layer were better in performance than the devices with the polymer only. (C) 2009 Elsevier B.V. All rights reserved.

An internally-matched GaN HEMTs device with 45.2 W at 8 GHz for X-band application

Optimized AlGaN/AlN/GaN high electron mobility transistor (HEMT) with high mobility GaN channel layer structures were grown on 2-in. diameter semi-insulating 6H-SiC substrates by MOCVD. The 2-in. diameter GaN HEMT wafer exhibited a low average sheet resistance of 261.9 Omega/square, with the resistance un-uniformity as low as 2.23%. Atomic force microscopy measurements revealed a smooth AlGaN surface whose root-mean-square roughness is 0.281 nm for a scan area of 5 x 5 mu m. For the single-cell HEMTs device of 2.5-mm gate width fabricated using the materials, a maximum drain current density of 1.31 A/mm, an extrinsic transconductance of 450 mS/mm, a current gain cutoff frequency of 24 GHz and a maximum frequency of oscillation 54 GHz were achieved. The four-cell internally-matched GaN HEMTs device with 10-mm total gate width demonstrated a very high output power of 45.2 W at 8 GHz under the condition of continuous-wave (CW), with a power added efficiency of 32.0% and power gain of 6.2 dB. To our best knowledge, the achieved output power of internally-matched devices are the state-of-the-art result ever reported for X-band GaN-based HEMTs. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.

Tuning of plasmon propagation in two-dimensional electrons

It is shown theoretically that the propagation of plasmons can be tuned by an external electric field via spin-orbit interactions in a two-dimensional electron gas formed in a semiconductor heterostructure. This may provide a manageable way of transmitting quantum information in a quantum device. A possible plasmon field effect transistor is proposed.