Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

High-performance, organic nanowire phototransistors open the way for optoelectronic device miniaturization

13.03.2013
Research team of Ulsan National Institute of Science and Technology (UNIST), Ulsan, South Korea, developed high-performance organic phototransistors (OPTs) based on single-crystalline n-channel organic nanowires.
Phototransistors are a kind of transistors in which the incident light intensity can modulate the charge-carrier density in the channel. Compared with conventional photodiodes, phototransistors enable easier control of light-detection sensitivity without problems such as the noise increment. However, to date, the research has mostly focused on thin-film OPTs, and nanoscale OPTs have scarcely been reported.

OPTs have many intrinsic advantages over their inorganic counterparts, such as the chemical tunability of optoelectronic properties by molecular design and high potential in low cost, light-weight, flexible applications.

Single-crystalline nano-/microwires (NWs/MWs) based on organic semiconductors have attracted great interest recently as they are promising building blocks for various electronic and optoelectronic applications. In particular, OPTs based on single-crystalline NWs/MWs may yield higher light sensitivity than their bulk counterparts. In addition, their one-dimensional, intrinsically defect-free and highly ordered nature will allow a deeper understanding of the fundamental mechanisms of charge generation and transport in OPTs, while enabling a bottom-up fabrication of optoelectronic nanodevices

Prof. Joon Hak Oh and Hojeong Yu, working at UNIST, together with Prof. Zhenan Bao at Stanford University, USA, have worked on n-channel single-crystalline nanowire organic phototransistors (NW-OPTs) and observed significant enhancement in the charge-carrier mobility of NW-OPTs.

Prof. Oh said, ¡°The development of OPTs based on n-channel single-crystalline organic semiconducting NWs/MWs is highly desirable for the bottom-up fabrication of complementary metal oxide semiconductor (CMOS)-like photoelectronic circuits, which provides various advantages such as high operational stability, easy control of photoswitching voltages, high photosensitivity and responsivity.¡±

The photoelectronic characteristics of the single-crystalline NW-OPTs such as the photoresponsivity, the photo-switching ratio, and the photoconductive gain, were analyzed from the I-V characteristics coupled with light irradiation and compared with those of vacuum-deposited thin-film devices. The external quantum efficiencies (EQEs) were also investigated for the NW-OPTs and thin-film OPTs. In addition, they calculated the charge accumulation and release rates from deep traps, and investigated the effects of incident light intensity on their photoelectronic properties.

A mobility enhancement is observed when the incident optical power density increases and the wavelength of the light source matches the light-absorption range of the photoactive material. The photoswitching ratio is strongly dependent upon the incident optical power density, whereas the photoresponsivity is more dependent on matching the light-source wavelength with the maximum absorption range of the photoactive material.

NW-OPTs based on n-channel semiconductor, N,N ¡ä-bis(2-phenylethyl)-perylene-3,4:9,10-tetracarboxylic diimide (BPE-PTCDI), exhibited much higher external quantum efficiency (EQE) values (¡Ö7900 times larger) than thin-film OPTs, with a maximum EQE of 263 000%. This phenomena result from the intrinsically defect-free single-crystalline nature of the BPE-PTCDI NWs. In addition, an approach was devised to analyze the charge-transport behaviors using charge accumulation/release rates from deep traps under on/off switching of external light sources.

¡°Our approach to charge-accumulation/release-rate calculations could provide a fundamental understanding about charge-carrier-density variations under light irradiation, which subsequently enables in-depth study of OPTs,¡± said Prof. Oh, ¡°Hence organic single-crystalline NW-OPTs are a highly promising alternative to conventional thin-film-type photodiodes, and can effectively pave the way for optoelectronic device miniaturization.¡±

This research was supported by a National Research Foundation of Korea (NRF) Grant funded by the Ministry of Education, Science, and Technology (MEST), and the Global Frontier Research Center for Advanced Soft Electronics and published in Advanced Functional Materials (Title: High-Performance Phototransistors Based on Single-Crystalline n-Channel Organic Nanowires and Photogenerated Charge-Carrier Behaviors, 5 Feb 2013).

The article can be found at http://onlinelibrary.wiley.com/doi/10.1002/adfm.201201848/abstract

Eunhee Song | EurekAlert!
Further information:
http://www.unist.ac.kr

More articles from Materials Sciences:

nachricht Additive manufacturing reflects fundamental metallurgical principles to create materials
18.01.2019 | University of Sheffield

nachricht Brilliant glow of paint-on semiconductors comes from ornate quantum physics
17.01.2019 | Georgia Institute of Technology

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Ten-year anniversary of the Neumayer Station III

The scientific and political community alike stress the importance of German Antarctic research

Joint Press Release from the BMBF and AWI

The Antarctic is a frigid continent south of the Antarctic Circle, where researchers are the only inhabitants. Despite the hostile conditions, here the Alfred...

Im Focus: Ultra ultrasound to transform new tech

World first experiments on sensor that may revolutionise everything from medical devices to unmanned vehicles

The new sensor - capable of detecting vibrations of living cells - may revolutionise everything from medical devices to unmanned vehicles.

Im Focus: Flying Optical Cats for Quantum Communication

Dead and alive at the same time? Researchers at the Max Planck Institute of Quantum Optics have implemented Erwin Schrödinger’s paradoxical gedanken experiment employing an entangled atom-light state.

In 1935 Erwin Schrödinger formulated a thought experiment designed to capture the paradoxical nature of quantum physics. The crucial element of this gedanken...

Im Focus: Nanocellulose for novel implants: Ears from the 3D-printer

Cellulose obtained from wood has amazing material properties. Empa researchers are now equipping the biodegradable material with additional functionalities to produce implants for cartilage diseases using 3D printing.

It all starts with an ear. Empa researcher Michael Hausmann removes the object shaped like a human ear from the 3D printer and explains:

Im Focus: Elucidating the Atomic Mechanism of Superlubricity

The phenomenon of so-called superlubricity is known, but so far the explanation at the atomic level has been missing: for example, how does extremely low friction occur in bearings? Researchers from the Fraunhofer Institutes IWM and IWS jointly deciphered a universal mechanism of superlubricity for certain diamond-like carbon layers in combination with organic lubricants. Based on this knowledge, it is now possible to formulate design rules for supra lubricating layer-lubricant combinations. The results are presented in an article in Nature Communications, volume 10.

One of the most important prerequisites for sustainable and environmentally friendly mobility is minimizing friction. Research and industry have been dedicated...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Our digital society in 2040

16.01.2019 | Event News

11th International Symposium: “Advanced Battery Power – Kraftwerk Batterie” Aachen, 3-4 April 2019

14.01.2019 | Event News

ICTM Conference 2019: Digitization emerges as an engineering trend for turbomachinery construction

12.12.2018 | Event News

 
Latest News

Additive manufacturing reflects fundamental metallurgical principles to create materials

18.01.2019 | Materials Sciences

How molecules teeter in a laser field

18.01.2019 | Life Sciences

The cytoskeleton of neurons has been found to be involved in Alzheimer's disease

18.01.2019 | Health and Medicine

VideoLinks
Science & Research
Overview of more VideoLinks >>>