High-performance Phototransistors Research Articles

A self-assembled ultrathin crystalline polymer film for high performance phototransistors

The π-conjugated polymer, PQBOC8, can be easily assembled into a large-area crystalline ultrathin film at the CHCl3/water interface. A phototransistor based on this ultrathin film showed a large photoresponsivity of 970 A W(-1), and a photocurrent/dark current ratio of 1.36 × 10(4) under a very low white light irradiation.

High performance phototransistors based on single crystalline perylene-tetracarboxylic-dianhydride nanoparticle

Organic semiconducting devices suffer from grain boundary scattering, which can be responsible for low mobility and even mask intrinsic transport properties. In this letter, we show that devices containing only single grains give electron mobility 2–3 orders higher than that of conventional film-structured polycrystalline organic semiconductor transistors. The devices contain single perylene-tetracarboxylic-dianhydride nanoparticles embedded inside gated-nanopore structures. Since there is no inter-grain scattering, we obtain the highest reported electron mobility values of 0.08 cm2/Vs at 300 K and 0.5 cm2/Vs at 80 K. Consequently, the devices, when illuminated with ultraviolet, also yield a previously unrecorded high value of external quantum efficiency of 3.5 × 106.

Phototransistors and Photoswitches From an Ultraclosely $\pi$-Stacked Organic Semiconductor

In this letter, high-performance organic phototransistors and photoswitches based on an ultraclosely π-stacked organic semiconductor, i.e., titanyl phthalocyanine, are fabricated. The p-type transistor exhibited high performance with a hole mobility of ~ 4. 5 cm2·V-1·s-1 and an on/off ratio higher than 3.1 × 107. Phototransistors exhibited high-photoresponse properties with a responsivity at 10.5 A/W and a photosensitivity up to 2.7 × 105. The high performance of the devices showed their potential application in optoelectronic organic integrated circuits.

Synthesis of a Conjugated Polymer with Broad Absorption and Its Application in High-Performance Phototransistors

An amorphous copolymer (PBDT–BBT) of 4,8-bis(2-thienyl)benzo[1,2-b:4,5-b′]dithiophene and 5,5′-bibenzo[c][1,2,5]thiadiazole was synthesized by Stille coupling polymerization. PBDT–BBT exhibited good solution processability, excellent thermal stability with decomposition temperature of 437 °C, broad absorption (300–800 nm), deep HOMO level (−5.7 eV), and LUMO level (−3.7 eV). The microstructure order of PBDT–BBT thin films is not susceptible to thermal annealing temperature (80–200 °C). Field-effect transistors based on this polymer exhibited a charge-carrier mobility of 6 × 10–3 cm2 V–1 s–1, threshold voltage of −1 V, and on/off current ratio of 106 without any post-treatments. Thin film phototransistors of PBDT–BBT exhibited a photoresponsivity of 3200 mA W–1 and photocurrent/dark current ratio of 4 × 105.

High Performance Phototransistors of a Planar Conjugated Copolymer

A planar conjugated copolymer named HXS-1 was applied in thin film phototransistors. Similar to organic field-effect transistors using V(G) to control the source-drain current, in phototransistors, the light is used to substitute V(G) as an independent variable to control the output of the transistors to realize light detection and signal magnification in a single organic device. All devices exhibited high performance with an on/off ratio up to 4.6 × 10(4) (the highest on/off ratio of organic or polymer phototransistors), which could be assigned to i) the wide absorption features of HXS-1 in the whole UV-vis range, ii) the ideal HOMO energy level of HXS-1 (5.21 eV) to align with Au electrodes (5.2 eV) and iii) the high mobility of the polymer thin films (∼0.06 cm(2) /Vs). Moreover, the devices, both under continuous operation conditions and long term measurement conditions, exhibited excellent stability, indicating potential applications of the devices in polymer-based optoelectronics.

A High Performance Photodetector Suitable for Visible Light and Near Infrared Applications

In this work, the high performance phototransistor photodetector (PTPD) in commercial 0.35 µm SiGe bipolar junction transistor complementary metal oxide semiconductor (BiCMOS) process without altering any process step is demonstrated and analyzed. The device combines a surface photodetector (SPD) and a conventional SiGe heterojunction transistor (HBT). It is shown that the SPD enhances light absorption, especially for the blue light. With the proper bias configuration, the PTPD shows acceptable dark current and a bias voltage that can be as low as 0.3 V. The Emitter and SPD areas can be respectively designed to meet electrical and optical requirements without increasing the device capacitance. Besides, high responsivities of 5.69/9.47/7.11 A/W for 450/670/780 nm lights were achieved in the PTPD, which makes the device suitable for many applications.

Thick-layered etched-contact amorphous silicon transistors

We introduce a new thick-layered, etched-contact a-Si:H TFT (TLEC-TFT) structure which allows the use of thick a-Si:H layers without increasing the TFT contact resistance. This device facilitates the integration of high-performance TFTs and thick-layered photo-transistors in a-Si:H-based image sensors. The TLEC-TFT is fully compatible with the conventional TFT fabrication process and requires no extra masking steps. For low values of the drain-to-source voltage, our new TFT boosts the linear region current by two orders of magnitude over that of conventional TFTs with identically thick a-Si:H layers. By removing the adverse effects of contact resistance in transistors with thick a-Si:H layers, our TLEC-TFT design allows us to compare the performance of TFTs with thick and thin a-Si:H layers. We find that the width of the conduction-band tail decreases in thick-layered a-Si:H TFTs. This reduction in the width of the band tails results in an increase in the TFT mobility and subthreshold slope. Consequently, thick-layered, etched-contact TFTs possess higher overall current-drive capabilities compared to conventional, thin-layered TFTs. We present experimental evidence which correlates the width of the conduction-band tail to the density of as-deposited free carriers.

Comparison of partially relaxed InGaAs/GaAs based high performance phototransistors

We report on heterojunction phototransistors (HPTs) operating at GaAs substrate transparent wavelengths beyond 900 nm, utilizing a strained InGaAs quantum well based absorbing region. High performances have been measured with responsivities of ≊80 and 200 A/W at 10 and 50 μW, respectively. The results correspond to electrical current gains of up to 3000 for currents of ≊10 mA, the best reported results for such phototransistor structures. The effect of strain relaxation on device performance is examined, and it is seen that it can cause a degradation both in terms of the transistor and photodiode characteristics of the HPT.