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 Linear potentiometer LRW2/3 - Maximum precision with many measuring points
17.05.2017 | WayCon Positionsmesstechnik GmbH

nachricht First flat lens for immersion microscope provides alternative to centuries-old technique
17.05.2017 | Harvard John A. Paulson School of Engineering and Applied Sciences

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: Can the immune system be boosted against Staphylococcus aureus by delivery of messenger RNA?

Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.

Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....

Im Focus: A quantum walk of photons

Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.

The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....

Im Focus: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

Im Focus: World's thinnest hologram paves path to new 3-D world

Nano-hologram paves way for integration of 3-D holography into everyday electronics

An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

 
Latest News

How herpesviruses win the footrace against the immune system

26.05.2017 | Life Sciences

Water forms 'spine of hydration' around DNA, group finds

26.05.2017 | Life Sciences

First Juno science results supported by University of Leicester's Jupiter 'forecast'

26.05.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>