Field-effect Phototransistors Research Articles

Graphene and PbS quantum dot hybrid vertical phototransistor

A field-effect phototransistor based on a graphene and lead sulfide quantum dot (PbS QD) hybrid in which PbS QDs are embedded in a graphene matrix has been fabricated with a vertical architecture through a solution process. The n-type Si/SiO2 substrate (gate), Au/Ag nanowire transparent source electrode, active layer and Au drain electrode are vertically stacked in the device, which has a downscaled channel length of 250 nm. Photoinduced electrons in the PbS QDs leap into the conduction band and fill in the trap states, while the photoinduced holes left in the valence band transfer to the graphene and form the photocurrent under biases from which the photoconductive gain is evaluated. The graphene/QD-based vertical phototransistor shows a photoresponsivity of 2 × 103 A W−1, and specific detectivity up to 7 × 1012 Jones under 808 nm laser illumination with a light irradiance of 12 mW cm−2. The solution-processed vertical phototransistor provides a new facile method for optoelectronic device applications.

Highly Photosensitive Vertical Phototransistors Based on a Poly(3-hexylthiophene) and PbS Quantum Dot Layered Heterojunction

We fabricated a vertical field effect phototransistor with Au/Ag nanowires as the transparent source electrode and with vertically stacked layers of poly(3-hexylthiophene) (120 nm) and lead sulfide quantum dots (380 nm), which formed heterojunctions. The built-in electric field in the layered heterojunction aids the separation of photoinduced excitons, while the short channel enables efficient carrier transport across the active region. Both of these benefits enable a high photoperformance and fast photoresponse. This vertical phototransistor can be operated at room temperature with a low operation voltage of −1 V and is therefore energy-efficient. Further, it has a wide response spectrum from 400 to 2100 nm, a high photoresponsivity of more than 9 × 104 AW–1, and a high detectivity of up to 2 × 1013 Jones (cm Hz1/2 W–1) under infrared illumination. Additionally, this vertical phototransistor had a response time of 9 ms, which is faster than a previously reported lateral field effect phototransistor based...

Broadband Phototransistor Based on CH3NH3PbI3 Perovskite and PbSe Quantum Dot Heterojunction

Organic lead halide perovskites have received a huge amount of interest since emergence, because of tremendous potential applications in optoelectronic devices. Here field effect phototransistors (FEpTs) based on CH3NH3PbI3 perovskite/PbSe colloidal quantum dot heterostructure are demonstrated. The high light absorption and optoelectric conversion efficiency, due to the combination of perovskite and quantum dots, maintain the responsivities in a high level, especially at 460 nm up to 1.2 A/W. The phototransistor exhibits bipolar behaviors, and the carrier mobilities are determined to be 0.147 cm2V-1s-1 for holes and 0.16 cm2V-1s-1 for electrons. The device has a wide spectral response spectrum ranging from 300 to 1500 nm. A short photoresponse time is less than 3 ms due to the assistance of heterojunction on the transfer of photoexcitons. The excellent performances presented in the device especially emphasize the CH3NH3PbI3 perovskite-PbSe quantum dot as a promising material for future photoelectronic applications.

Interface Trap State Characterization of Metal-Insulator-Semiconductor Structures Based on Photosensitive Organic Materials

Flexible organic and printed electronics has led in the last years to exciting applications, especially for what concerns devices incorporating photosensitive materials. Among the latter, organic field-effect phototransistors are a promising technology because of the high light-sensitivity and the possibility of being integrated within more complex systems. Nevertheless, their optimization has not been thoroughly investigated and considerable variations are often observed in their behavior. In this framework, the most critical aspect is represented by the interface formed between the organic semiconductor and the employed dielectric layer. In our contribution, we have fabricated metal-insulator-semiconductor (MIS) structures based on the archetypal photosensitive organic materials poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) on Silicon/SiO2 substrates, exploiting their blend in a bulk heterojunction configuration. The MIS structures have been characterized by means of admittance spectroscopy to study the properties of the trap distribution at the interface between the organic semiconductors and the silicon oxide insulating layer. The complex behavior of the capacitance and loss diagrams has been interpreted with a simple electrical model to extract the density of the traps at the interface between the insulator and the semiconductor. It is shown that in the blend-based MIS device several peaks arise in the loss diagram with respect to the only P3HT MIS device. This could be attributed to a different interaction between the single species in the bulk heterojunction and the silicon oxide layer. Furthermore, the reported values of trap densities result in the range of those determined for analogous structures and materials.

High-performance PbS quantum dot vertical field-effect phototransistor using graphene as a transparent electrode

Solution processed photoactive PbS quantum dots (QDs) were used as channel in high-performance near-infrared vertical field-effect phototransistor (VFEpT) where monolayer graphene embedded as transparent electrode. In this vertical architecture, the PbS QD channel was sandwiched and naturally protected between the drain and source electrodes, which made the device ultrashort channel length (110 nm) simply the thickness of the channel layer. The VFEpT exhibited ambipolar operation with high mobilities of μe = 3.5 cm2/V s in n-channel operation and μh = 3.3 cm2/V s in p-channel operation at low operation voltages. By using the photoactive PbS QDs as channel material, the VFEpT exhibited good photoresponse properties with a responsivity of 4.2 × 102 A/W, an external quantum efficiency of 6.4 × 104% and a photodetectivity of 2.1 × 109 Jones at the light irradiance of 36 mW/cm2. Additionally, the VFEpT showed excellent on/off switching with good stability and reproducibility and fast response speed with a short rise time of 12 ms in n-channel operation and 10.6 ms in p-channel operation. These high mobilities, good photoresponse properties and simplistic fabrication of our VFEpTs provided a facile route to the high-performance inorganic photodetectors.

Short Channel Quantum Dot Vertical and Lateral Phototransistors

Quantum dot (QD) devices have been studied extensively as a significant platform for optoelectronic applications and photodetection, but the high efficient conversion from light to current requires high operating voltages, and has become a roadblock in a wide range of on chip applications. The main challenges rely on promoting light absorption and transportation efficiency, which occur in the same place—the channel. Here, the authors present short channel (SC) field effect phototransistors (FEpTs) by combing the QDs with the vertical architecture for the first time. These devices exhibit excellent performances in ultrahigh R of 1 × 105 A W−1, D* of 1.6 × 1013 Jones, effective quantum efficiency of 2.6 × 107% at low operating voltage of ±4 V under room temperature, and they strongly depend on channel length. It is found there was an optimal L to obtain high performances, due to the two roles of channel, light harvesting, and electric transportation, which give the negative and positive contributions to photocurrent, respectively. These SC QVFEpTs exhibit a great application in photodetection, from visible to infrared, moreover, the all‐solution fabricating process and lateral detection (determined by vertical architecture) provide a convenient pathway for low cost, integrated circuit architectural compatibility.

Hybrid Graphene–Si-Based Nanoscale Vacuum Field Effect Phototransistors

Two-dimensional (2D) hybrid nanoelectronic devices stem from the combination of 2D systems or a mixture of 2D materials themselves, such as graphene, with other well-defined nanostructures interacting with each other in the quantum regime and enabling exceptional characteristics. Here, this paper presents a hybrid photodetection platform consisting of a graphene/Si (Gr/Si) heterojunction in conjunction with nanoscale vacuum electronics based on a graphene/SiO2/Si (GrOS) field effect device. The responsivity of the hybrid platforms based on p-Si and n-Si is fully and finely tunable up to 1.2 and 0.45 A/W, respectively, which correspond to external (internal) quantum efficiencies of 235% (350%) and 88% (132%), respectively. The multiplication gain in the proposed hybrid device originates from the impact ionization initiated by photoinduced carrier injection into the self-induced localized electric field (up to ∼106 V/cm) distributed in a 2DEG region in Si. The electrons travel from the Si edge to graphene v...

High performance PbSe colloidal quantum dot vertical field effect phototransistors

Here, vertical field effect phototransistors (VFEPTs) based on lead selenide colloidal quantum dots (PbSe CQDs) for infrared photo detection were investigated, using Au/Ag nanowires as the source transparent electrode. VFEPTs have the advantage of easy fabrication of ultrashort channel length devices, as the channel length is simply determined here by the PbSe CQDs active layer’s thickness (260 nm). In ultrashort channels, photo-excited carriers quickly (in nanoseconds) transfer to the drain. As soon as a hole (electron) reaches the drain, a hole (electron) is replenished from the source. Accordingly, multiple holes circulate in the ultrashort channel following a single electron–hole photo generation. As a result, the device exhibits superior photoconductive properties over the lateral structure. PbSe CQD VFEPTs show ambipolar operation under low voltage down to one volt at room temperature. Moreover, high photo responsivity and high specific detectivity of 2 × 104 A W−1 and 7 × 1012 Jones are also achieved in the devices under 808 nm laser illumination. The transparent electrode-based near infrared VFEPTs prepared through this self-assembly solution process show promise for applications in electronics and photoelectronics.

Study of the preparation and spectral response of stacked graphene nanoribbon-carbon nanotube-based phototransistors

Narrow graphene nanoribbon-carbon nanotube (GNR-CNT) stacks were prepared by the plasma unzipping of single-wall carbon nanotubes (SWCNT). A mix-and-match method was developed for the fabrication of nanosized devices in a microsized chip, and the optoelectronic properties of highly sensitive back-gated field-effect phototransistors (FETs) based on the GNR-CNT stack were evaluated. The photoresponse of the representative phototransistors improved near the Dirac point voltage for flat and thick long channels, with an ultrahigh spectral response of 10–50 A W−1 using over wavelength measurement at room temperature. The channel current of FETs decreased from 10−11 A to 10−15 A with the decrease in temperature, indicating the semiconducting potential of stacks. Because of the high spectral response of GNR-CNT stacks, they can be used as the optical elements in nanosized photoelectric devices such as phototransistors.

Improved photoelectronic performance of graphene, polymer and PbSe quantum dot infrared photodetectors

We fabricated a highly sensitive infrared (IR) layer-heterojunction field effect phototransistor (LH-FEpT) by integrating poly [2-methoxy-5-(20-ethylhexyloxy-p-phenylenevinylene)] (MEH-PPV)/PbSe quantum dots composite with monolayer graphene. The phototransistor exhibited high photosensitive in a wide spectral range from visual to infrared. The graphene/MEH-PPV/PbSe QDs based FEpT (GMQ-FEpT) show high carrier mobility (μ) up to 1800cm2V−1s−1, high photo responsivity (R) about 133A/W at a light intensity (4.9mW/cm2), high external quantum efficiency (EQE) (up to 2×104%) and high specific detectivity (D*) (9.8×1010Jones) under illumination of 808nm laser.

Field-Effect Phototransistors Based on Graphene-Quantum Dot Hybrids

Field effect photo-transistors (FEpTs) based on graphene-PbSe quantum dot (QD) hybrids have been designed and fabricated. By electrical and photoelectrical measurements, the carrier mobilities reached to 1621 cm 2 V -1 s -1 for electrons and 1228 cm 2 V -1 s -1 for holes, the photoresponsivity (R) achieved to 1 AW -1 , and the photoresponse time (τ 1 ) was 0.7 s when the photocurrent came to about 80%. Therefore, the FEpTs based on graphene-QD hybrids have shown broad application prospects.

Ultrasensitive 1D field-effect phototransistors: CH3NH3PbI3 nanowire sensitized individual carbon nanotubes.

Field-effect phototransistors were fabricated based on individual carbon nanotubes (CNTs) sensitized by CH3NH3PbI3 nanowires (MAPbI3NWs). These devices represent light responsivities of R = 7.7 × 10(5) A W(-1) under low-lighting conditions in the nW mm(-2) range, unprecedented among CNT-based photodetectors. At high incident power (∼1 mW mm(-2)), light soaking results in a negative photocurrent, turning the device insulating. We interpret the phenomenon as a result of efficient free photoexcited charge generation and charge transfer of photoexcited holes from the perovskite to the carbon nanotube. The charge transfer improves conductance by increasing the number of carriers, but leaves electrons behind. At high illumination intensity their random electrostatic potential quenches mobility in the nanotube.

Multiheterojunction Phototransistors Based on Graphene–PbSe Quantum Dot Hybrids

Graphene-semiconductor quantum dot (QD) hybrid field effect phototransistors (FEpTs) have attracted much interest due to their ultrahigh gain and responsivity in photo detection. However, most reported results are based on single-layer heterojunction, and the multiheterojunction FEpTs are often ignored. Here, we design two typical multiheterojunction FEpTs based on graphene–PbSe quantum dot (QD) hybrids, including QD at the bottom layer (QD-bottom) and graphene at the bottom layer (G-bottom) FEpTs. Through a comparative study, G-bottom FEpTs showed a multisaturation behavior due to the multigraphene layer effect, which was absent in the QD-bottom FEpTs. The mobilities for electrons and holes were μE = 147 cm2 V–1 s–1 and μE = 137 cm2 V–1 s–1 in the G-bottom FEpTs and μE = 14 cm2 V–1 s–1 and μE = 59 cm2 V–1 s–1 in the QD-bottom FEpTs. Higher responsivity (∼106 A W–1) and faster response rate were both achieved by the G-bottom FEpTs. All of the advantages in G-bottom FEpTs were attributed to the back-gate e...

Comparison of photoresponse of transistors based on graphene-quantum dot hybrids with layered and bulk heterojunctions

Phototransistors based on graphene–quantum dot hybrids have a high responsivity and gain. However, the influence of the type of heterojunction on the photoresponse of the transistors is still undetermined. A comparison was performed on field-effect phototransistors (FEpTs) with two types of heterojunctions: layered heterojunctions (LHs) and bulk heterojunctions (BHs). Through a comparative study, it was shown that BH–FEpTs had electron and hole mobilities (μE and μH) of 677 and 527 cm2 V−1 s−1 whereas LH–FEpTs had lower mobilities of μE = 314 cm2 V−1 s−1 and μH = 367 cm2 V−1 s−1. The large interfacial area in the BHs reduced the degree of channel order (α) by two orders of magnitude compared with the LHs. Although a higher mobility was achieved, an increase in the degree of channel disorder and the lack of an effective transfer mechanism limits the responsivity in BH–FEpTs. Therefore, LH–FEpTs are more appropriate candidates for near infrared phototransistors.

Bulk- and layer-heterojunction phototransistors based on poly [2-methoxy-5-(2′-ethylhexyloxy-p-phenylenevinylene)] and PbS quantum dot hybrids

The responsivity (R) of a thin film photodetector is proportional to the product of its photo-induced carrier density (n) and mobility (μ). However, when choosing between layer heterojunction (LH) and bulk heterojunction (BH) field-effect phototransistors (FEpTs), it is still unclear which of the two device structures is more conducive to photodetection. A comparison study is performed on the two structures based on polymer and PbS quantum dot hybrids. Both devices exhibit ambipolar behavior, with μE ≈ μH = 3.7 cm2 V−1 s−1 for BH-FEpTs and μH = 36 cm2 V−1 s−1 and μE = 52 cm2 V−1 s−1 for LH-FEpTs. Because of the improvements in μ and the channel order degree (α), the responsivity of LH-FEpTs is as high as 101 A/W, which is as much as two orders of magnitude higher than that of BH-FEpTs (10−1A/W) under the same conditions. Although the large area of the BH improves both the exciton separation degree (β) and n in the BH-FEpT, the lack of an effective transport mechanism becomes the main constraint on high device responsivity. Therefore, LH-FEpTs are better candidates for use as photo detectors, and a “three-high” principle of high α, β, and μ is found to be required for high responsivity. At the request of the authors, this article is being retracted effective 23 February 2017.

High aspect ratio conjugated polymer nanowires for high performance field-effect transistors and phototransistors.

We synthesized a highly crystalline DPP-based polymer, DPPBTSPE, which contained 1,2-bis(5-(thiophen-2-yl)selenophen-2-yl)ethene as a planar and rigid electron donating group. High- and low-molecular weight (MW) DPPBTSPE fractions were collected by Soxhlet extraction and were employed to investigate their unique charge transport properties in macroscopic films and single crystalline polymer nanowire (SC-PNW), respectively. The low-MW polymer could provide well-isolated and high aspect ratio SC-PNWs, in which the direction of π-π stacking was perpendicular to the wire growing axis. The field effect transistors made of SC-PNWs exhibited remarkably high carrier mobility of 24 cm(2) V(-1) s(-1). In addition, phototransistors (PTs) made of SC-PNW showed very high performance in terms of photoresponsivity (R) and photoswitching ratio (P). The average R of the SC PNW-based PTs were in the range of 160-170 A W(-1) and the maximum R was measured at 1920 A W(-1), which is almost three orders higher than that of thin film-based PT device.

Wide spectral response field effect phototransistor based on graphene-quantum dot hybrid

The photoelectrical characteristics of field-effect phototransistors (FEPTs) are investigated experimentally based on a graphene–PbS quantum dot (QD) hybrid. The device presented a wide spectral response range from 300 to 1400 nm because of multiple-exciton generation of PbS QDs. The photoelectrical responsivity reached up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$2\times 10^{5}\ \hbox{A/W}$</tex-math></inline-formula> at low bias voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$\sim$</tex-math></inline-formula> 10 mV) and became more sensitive with increasing bias voltage. The transient response of the hybrid FEPTs was also measured with the relaxation times and the decay times around several seconds. Such devices exhibit great competitiveness in wide spectral response, flexible integrated circuits with low cost, large area, low energy consumption, and high responsivity.

Strain and structure heterogeneity in MoS2 atomic layers grown by chemical vapour deposition.

Monolayer molybdenum disulfide (MoS2) has attracted tremendous attention due to its promising applications in high-performance field-effect transistors, phototransistors, spintronic devices and nonlinear optics. The enhanced photoluminescence effect in monolayer MoS2 was discovered and, as a strong tool, was employed for strain and defect analysis in MoS2. Recently, large-size monolayer MoS2 has been produced by chemical vapour deposition, but has not yet been fully explored. Here we systematically characterize chemical vapour deposition-grown MoS2 by photoluminescence spectroscopy and mapping and demonstrate non-uniform strain in single-crystalline monolayer MoS2 and strain-induced bandgap engineering. We also evaluate the effective strain transferred from polymer substrates to MoS2 by three-dimensional finite element analysis. Furthermore, our work demonstrates that photoluminescence mapping can be used as a non-contact approach for quick identification of grain boundaries in MoS2.

Integration of Ni&lt;sub&gt;2&lt;/sub&gt;Si/Si Nanograss Heterojunction on n-MOSFET to Realize High-Sensitivity Phototransistors

We report a top-down fabrication technique for direct integration of Ni 2 Si/Si heterojunction arrays on n-type MOSFET gate terminal to realize sensitive field-effect phototransistors (PTs). It was observed that exposing gate area to light (λ = 655 nm) leads to significant modulation of threshold voltage (V TH ) of PT in comparison with a conventional MOSFET. By analyzing optical absorption spectra of Ni 2 Si/Si nanostructures on SiO 2 of this novel PT and planar Ni 2 Si/poly-Si on SiO 2 of conventional transistors, we concluded that, nanostructures strongly improve light absorption. This results in higher optically generated electron-hole pairs in which excess holes induce an electric field on the transistor channel and help the threshold happen at lower voltages. To recognize the appropriate operating point of such nanostructure-based PT, effect of V GS on the sensitivity of drain current was investigated. Experimental results show that device sensitivity (S) is related to gate-source voltage via a homographic like function. Theoretical analysis shows S ∝ 1/(V GS - V TH ) for high V GS , which has been confirmed by experimental data. In addition, external quantum efficiency and photoresponsivity of PT as functions of gate voltage were studied. The achieved results suggest that this device would be a promising candidate for fabricating low-power PTs based on silicide nanostructures.

High photosensitivity few-layered MoSe2 back-gated field-effect phototransistors

In this paper, we report on the fabrication and optoelectronic properties of high sensitive phototransistors based on few-layered MoSe2 back-gated field-effect transistors, with a mobility of 19.7 cm2 V−1 s−1 at room temperature. We obtained an ultrahigh photoresponsivity of 97.1 AW−1 and an external quantum efficiency (EQE) of 22 666% using 532 nm laser excitation at room temperature. The photoresponsivity was improved near the threshold gate voltage; however, the selection of the silicon dioxide as a gate oxide represents a limiting factor in the ultimate performance. Thanks to their high photoresponsivity and external quantum efficiency, the few-layered MoSe2-based devices are promising for photoelectronic applications.