Field-effect Phototransistors Research Articles

Role of Ga Vacancy on a Multilayer GaTe Phototransistor

We report a high-performance field-effect transistor (FET) and phototransistor based on back-gated multilayer GaTe nanosheets. Through both electrical transport measurements at variable temperatures and first-principles calculations, we find Ga ion vacancy is the critical factor that causes high off-state current, low on/off ratio, and large hysteresis of GaTe FET at room temperature. By suppressing thermally activated Ga vacancy defects at liquid nitrogen temperature, a GaTe nanosheet FET with on/off ratio of ∼10(5), off-state current of ∼10(-12) A, and negligible gate hysteresis is successfully demonstrated. Furthermore, a GaTe phototransistor with high photogain above 2000 and high responsivity over 800 AW(-1) is achieved, as well. Our findings are of scientific importance to understand the physical nature of intrinsic GaTe transistor performance degradation and also technical significance to unlock the hurdle for practical applications of GaTe transistors in the future.

Gate dependent photo-responses of carbon nanotube field effect phototransistors

Gate dependent photoconductivity of carbon nanotube (CNT) field effect phototransistors (FEPs) was systematically investigated in this study. The photo-response comparisons of CNT FEPs with symmetric and asymmetric metal structures connecting to the same CNT revealed that the gate effect contributed to a sensitivity improvement with a lower dark current, a higher photocurrent, and an enhanced photovoltage. A functionalized asymmetric FEP, fabricated by partially doping the CNT utilizing a polyethylene imine (PEI) polymer, verified that FEPs delivered a better performance by using asymmetric structures. A multi-gate FEP, with three pairs of side-gates that can electrostatically dope different sections of a CNT independently, was fabricated to examine the gate structure dependent photo-responses. Experimental measurements showed an unconventional photocurrent improvement that was weakly dependent on the gate location, which was attributed to the unique charge distribution of one-dimensional semiconductors.

Thin-Film Phototransistor with nc-Si:H/a-Si:H Bilayer Channel

ABSTRACTThere is significant interest in optical sensors whose fabrication process is fully compatible with existing flat panel display thin film transistor (TFT) technology. Here, we report a field-effect phototransistor with a channel comprising a thin nanocrystalline silicon (nc-Si:H) transport layer and a thicker hydrogenated amorphous silicon (a-Si:H) absorption layer. The implementation of nc-Si:H layer improves device stability in comparison with a-Si:H phototransistors, resulting in reduced threshold voltage shift. Semiconductor and dielectric layers were deposited by radio-frequency plasma enhanced chemical vapor deposition at 280°C. The device characterization included the dark and light transfer characteristics, spectral-response and dynamic measurements. The external quantum efficiency was measured as a function of incident photon flux at different biasing conditions. The phototransistor with channel length of 24 microns and photosensitive area of 1.4 mm2shows an off-current of about 1 pA, and photo-conductive gain up to 200 at low incident intensities. Thus, the results demonstrate the feasibility of the phototransistor for low light level detection.

Thin Film Field‐Effect Phototransistors from Bandgap‐Tunable, Solution‐Processed, Few‐Layer Reduced Graphene Oxide Films

Thin film field-effect phototransistors (FETs) can be developed from bandgap-tunable, solution-processed, few-layer reduced graphene oxide (FRGO) films. Large-area FRGO films with tunable bandgaps ranging from 2.2 eV to 0.5 eV can be achieved readily by solution-processing technique such as spin-coating. The electronic and optoelectronic properties of FRGO FETs are found to be closely related to their bandgap energy. The resulting phototransistor has great application potential in the field of photodetection.

Phototransistor with nanocrystalline Si/amorphous Si bilayer channel

We report a field-effect phototransistor with a channel comprising a thin nanocrystalline silicon transport layer and a thicker hydrogenated amorphous silicon absorption layer. The semiconductor and dielectric layers were deposited by radio-frequency plasma enhanced chemical vapor deposition. The phototransistor with channel length of 24 microns and photosensitive area of 1.4 mm2 shows an off-current of about 1 pA, and high photoconductive gain in the subthreshold region. Measurements of the quantum efficiency at different incident light intensities and biasing conditions, along with spectral-response characteristics, and threshold voltage stability characterization demonstrate the feasibility of the phototransistor for low light level detection.

Connecting Organic Nanowires

In this work we report on a universal methodology for connecting organic nanowires and nanosheets formed by p-conjugated molecules viametal nanoparticles. We present a brief study on the electrical characteristics of the thus connected nanowires carried out in a four-tip-STM manipulation and measurement system (4TMMS; STM1⁄4 scanning tunneling microscopy) under ultrahigh vacuum (UHV) conditions. The recent developments in organic semiconducting nanostructures have permitted important advances in the fabrication of low-cost, large-area, flexible optic and microelectronic devices. In fact, over the last few years the use of p-conjugated molecules as building blocks for such organic nanostructures has received special attention and interest. Within the class of p-conjugated molecules, the families of metallo porphyrins, metallo phthalocyanines, and perylenes are promising materials for varying applications such as vapor (gas) nanosensors and as active components for photonic devices, organic field effect transistors (OFETs), phototransistors, and solar cells. It has been realized that the fabrication of hybrid organic!inorganic materials comprising semiconducting organic nanowires and metal particles opens new routes in the design of devices’ functionality. Such hybrid materials may provide a ideal model system for the study of organic!inorganic nanomaterials. Despite this promising prospect, only very few works exist regarding the formation of organic semiconducting nanofibers!metal particles hybrid systems. ] In this Communication, we present a significant step forward in the fabrication of nanowire–metal–nanowire junctions by using metal nanoparticle-decorated organic nanowires as a base for the growth of secondary nanowires in such a way that a new route for the fabrication of connected organic single-crystal nanowires is demonstrated. First, we describe the organic/inorganic hybrid nanostructures prepared by decorating single-crystal organic nanowires with metal particles in a one-step dry process at room temperature. In a second step we demonstrate an unprecedented class of heterostructured nanowires formed by connection through metal nanoparticles of different organic nanostructures. Finally, the electrical conductivity of these connected nanowires is studied in a 4TMMS. Preparation of Hybrid and Connected Nanowires: Recently, we have reported a universal method for the growth of squared nanowires and nanobelts formed by p-conjugated molecules on

The Ring-Shaped CMOS-Based Phototransistor With High Responsivity for the UV/Blue Spectral Range

The ring-shaped phototransistor with a floating bulk enclosed by a ring-shaped photodiode is proposed to enhance the responsivity for the ultraviolet/blue spectral range. The P-channel metal-oxide-semiconductor field-effect transistor and N-channel metal-oxide-semiconductor field-effect transistor phototransistors were manufactured using a standard 0.35-mum complimentary metal-oxide-semiconductor (CMOS) technology. When the phototransistors were illuminated with 400-nm light, the measurement results for 3-V bias demonstrated a responsivity higher than 1500 A/W, which is also superior to that of other reported photodetectors manufactured using a standard CMOS technology. Even for very small bias voltages such as 0.1 V, the phototransistor can exhibit a responsivity of 17.9 A/W.

Graphene bilayer field-effect phototransistor for terahertz and infrared detection

A graphene bilayer phototransistor (GBL-PT) is proposed and analyzed. The GBL-PT under consideration has the structure of a field-effect transistor with a GBL as the channel and the back and top gates. The positive bias of the back gate results in the formation of conducting source and drain sections in the channel, while the negatively biased top gate provides the potential barrier which is controlled by the charge of the photogenerated holes. The features of the GBL-PT operation are associated with the variations of both the potential distribution and the energy gap in different sections of the channel when the gate voltages and the charge in the barrier section change. Using the developed GBL-PT device model, the spectral characteristics, dark current, responsivity and detectivity are calculated as functions of the applied voltages, energy of incident photons, intensity of electron and hole scattering, and geometrical parameters. It is shown that the GBL-PT spectral characteristics are voltage tuned. The GBL-PT performance as photodetector in the terahertz and infrared photodetectors can markedly exceed the performance of other photodetectors.

Silicon nanowire networks for the application of field effect phototransistor

A random network of silicon nanowires was synthesized on Si3N4/Si substrate via a catalytic reaction in N2 atmosphere at 1000 °C using a parallel plate structure. The nanowires were completely amorphous with an average diameter of 40–80 nm. A commercial high-brightness light emitting diodes was used as the light source in the gate of the field effect phototransistor. It was found that drain current was proportional to the light intensity. It is suggested that the current gain of the photoresponse under the red light illumination is smaller compared to that under the blue light illumination. The maximal current gain increases approximately 30 times under the blue light illumination.

Wavelength-selective organic field-effect phototransistors based on dye-doped poly-3-hexylthiophene

The authors present a strategy to manufacture wavelength-selective field-effect phototransistors by employing dye-doped poly-3-hexylthiophene (P3HT) as a semiconducting layer. The dye doping of the semiconductor P3HT was achieved by blending organic molecules—coumarin 6, oxazine 1, and nile red—into the conjugated organic polymer. Illuminating these transistors with monochromatic light in the range of 400–700nm resulted in varying conductivities for certain wavelengths in dependence on the particular dye. This effect is attributed to the photogeneration of excitons on the dye molecules, which are subsequently transferred to the conjugated polymer.

High quantum efficiency strained InGaAs/AlGaAs quantum-well resonant-cavity inversion channel bipolar field-effect phototransistor

A high-efficiency, resonant-cavity, bipolar inversion channel field-effect transistor detector is demonstrated with a triple-strained InGaAs quantum-well absorbing region. A quantum efficiency of 80% is obtained at a resonant wavelength of 0.94 μm, and a bandwidth of 20 Å, giving a 26-fold enhancement in absorption due to resonance. The transistor detector operates in the FET mode with an independent gate electrode to control its sensitivity, and in a bipolar mode with a photogain of 25. The structure is identical to that used in other inversion channel laser structures, and hence provides an optimum configuration for optoelectronic integration. This is the first demonstration of a three-terminal quantum-well resonant-cavity photodetector.

Amorphous silicon phototransistors

An amorphous silicon field-effect phototransistor is fabricated using a processing technology compatible with conventional amorphous silicon-silicon nitride thin-film transistors. The phototransistor has an offset structure between the source and gate electrodes, where light is absorbed to produce a photocurrent. In an electron accumulation mode, the photocurrent is greater than the dark current by three orders of magnitude. In addition, the phototransistor is found to have output characteristics showing good saturation. Typical photoconductive gain of this saturation current is 17.

Photogating of ionic currents across a lipid bilayer.

Photoformation of metalloporphyrin cations in a lipid bilayer increases the ionic currents of negative and decreases those of positive hydrophobic ions. At low concentrations of the mobile hydrophobic ion, a 30% change in conductivity is observed that decreases with increasing concentration of positive tetraphenylphosphonium ion and increases drastically with increasing concentration of negative tetraphenylboride ion. In the region of saturated conductance of boride ion, the increase in conductivity is 3.6-fold. A 15-fold increase is observed with the protonophore carbonyl cyanide 3-chlorophenylhydrazone. In this case the net charge gated is 300 times greater than the photogenerated charge in the bilayer membrane. Thus there is a net gain in this organic field effect phototransistor. The gating can also be accomplished by continuous light or chemical oxidants. Photogating is explained as space charge effects inside the bilayer.