Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

An old dream has been fulfilled: Zinc oxide as semiconductor

05.12.2008
Zinc oxide is a "jack of all trades" - thousands of tons thereof are produced all over the world every year. Its fields of utilization range from food additive to sun screening agents.

It is even significant as semiconductor, although the great breakthrough in this field is yet to come. Perfect doping is not yet possible. A team of chemical scientists at the Ruhr-University in Bochum, working under the auspices of Prof. Christof Wöll, is a step closer to unveiling the reason. They were experimentally able to provide evidence that hydrogen atoms disturb the process.

Controlled concentration of hydrogen atoms during the production of intrinsic zinc oxide is thus the key to the routine use of ZnO as semiconductor. The scientists have documented their results in the journal Physical Review Letters.

Doping activates the semiconductor

Doping, i.e. the insertion of specific foreign atoms into the crystal lattice of a solid, is the most important factor during the production of semiconductor devices. These foreign atoms either release an electron (n-doping), or absorb an electron, thus creating a "hole" in the solid (p-doping). These mobile electrons or holes then bring about the electric conductivity of the otherwise isolated semiconductor, i.e. doping initiates "action" in the semiconductor. This standard process in the manufacturing of conventional semiconductors e.g. silicon or germanium has however been problematic for zinc oxide to date. In particular, it has been difficult to achieve p-doping, which made it impossible to construct semiconductor devices such as transistors or light emitting diodes (LEDs). Such devices require a pn-transition, a junction between the p-doped and the n-doped zones. Thus, in the field of semiconductors, zinc oxide is at present only used for a few special applications.

Hydrogen is always present

There has been a significant improvement in the production of intrinsic zinc oxide during the past few years. Blue LEDs made of zinc oxide have only been presented recently. There are, however, still numerous problems concerning doping. Research scientists at the Ruhr-University in Bochum have been able to identify a significant obstacle in the production of intrinsic zinc oxide. During experiments, which had actually been motivated by an interest in the catalytic properties of ZnO, they were able to show that hydrogen atoms always result in n-doping. They could reversibly dope zinc oxide substrates using hydrogen and then eliminate the hydrogen by heating. The scientists were thus able to verify theoretical predictions made in 2000. They used a special technique for measurements at diverse temperatures to verify the corresponding charge carrier concentrations. A sufficiently high density of these charge carriers is essential for the proper functioning of electronic devices. Hydrogen impurities are almost impossible to avoid during the production process, thus preventing the targeted p-doping. The electrons released from the H atoms to the ZnO immediately fill the holes caused by the p-doping. High purity, in particular a hydrogen-free environment, is thus a decisive factor for the production of intrinsic zinc oxide.

Controversy is history

The research team was thus also able to resolve a scientific controversy: to date it has often been postulated that the doping problems are caused by imperfections in the zinc oxide crystal lattice, by additional Zn atoms or oxygen defects. The results obtained in Bochum are a basis for the production of higher performance ZnO-based electronic circuits. Currently the scientists are doing intensive research to attain p-doping with an intrinsic, i.e. hydrogen-free, zinc oxide substrate by incorporating appropriate foreign atoms.

Technology actually intended for another purpose

The technology used, a special version of electron spectroscopy, is normally used for another purpose, namely for the investigation of chemical processes on the surfaces of zinc oxides. Such phenomena have been investigated at the Ruhr-University in Bochum for many years within the frameworks of SFB 558 (Focus Research Centre - Metal-Substrate Interactions in Heterogeneous Catalysis) due to the significance of zinc oxide for heterogeneous catalysis, particularly for the synthesis of methanol.

Title

H. Qiu, B. Meyer, Y. Wang, Ch. Wöll: Ionization energies of shallow donor states in ZnO created by reversible formation and depletion of H interstitials. In: Physical Review Letters 101, 236401 (2008), DOI: 10.1103/PhysRevLett.101.236401

Further Information

Prof. Christof Wöll, Department of Physical Chemistry I at the Ruhr-University Bochum, D-44780 Bochum, Germany, Tel: +49 (0) 234/32-25529, Fax: +49 (0) 234/32-14182, E-Mail: woell@pc.ruhr-uni-bochum.de

Dr. Josef König | idw
Further information:
http://www.pc.rub.de

More articles from Power and Electrical Engineering:

nachricht Agricultural insecticide contamination threatens U.S. surface water integrity at the national scale
06.12.2018 | Universität Koblenz-Landau

nachricht Improving hydropower through long-range drought forecasts
06.12.2018 | Schweizerischer Nationalfonds SNF

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

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

Im Focus: Topological material switched off and on for the first time

Key advance for future topological transistors

Over the last decade, there has been much excitement about the discovery, recognised by the Nobel Prize in Physics only two years ago, that there are two types...

Im Focus: Researchers develop method to transfer entire 2D circuits to any smooth surface

What if a sensor sensing a thing could be part of the thing itself? Rice University engineers believe they have a two-dimensional solution to do just that.

Rice engineers led by materials scientists Pulickel Ajayan and Jun Lou have developed a method to make atom-flat sensors that seamlessly integrate with devices...

Im Focus: Three components on one chip

Scientists at the University of Stuttgart and the Karlsruhe Institute of Technology (KIT) succeed in important further development on the way to quantum Computers.

Quantum computers one day should be able to solve certain computing problems much faster than a classical computer. One of the most promising approaches is...

Im Focus: Substitute for rare earth metal oxides

New Project SNAPSTER: Novel luminescent materials by encapsulating phosphorescent metal clusters with organic liquid crystals

Nowadays energy conversion in lighting and optoelectronic devices requires the use of rare earth oxides.

Im Focus: A bit of a stretch... material that thickens as it's pulled

Scientists have discovered the first synthetic material that becomes thicker - at the molecular level - as it is stretched.

Researchers led by Dr Devesh Mistry from the University of Leeds discovered a new non-porous material that has unique and inherent "auxetic" stretching...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

New Plastics Economy Investor Forum - Meeting Point for Innovations

10.12.2018 | Event News

EGU 2019 meeting: Media registration now open

06.12.2018 | Event News

Expert Panel on the Future of HPC in Engineering

03.12.2018 | Event News

 
Latest News

Electronic evidence of non-Fermi liquid behaviors in an iron-based superconductor

11.12.2018 | Physics and Astronomy

Topological material switched off and on for the first time

11.12.2018 | Materials Sciences

NIST's antenna evaluation method could help boost 5G network capacity and cut costs

11.12.2018 | Information Technology

VideoLinks
Science & Research
Overview of more VideoLinks >>>