Research report 1999


This is our 6th web-based research report since we went 'online' in 1994. Since then, our website has attracted a lot of attention from all over the world and meanwhile serves as an information source not only for our physics colleagues and interested students but also for those out there, who simply want to know on which subjects their 'tax Euros' are working. We appreciate the tremendous activity on our server and do encourage everybody to come by and stay for a while - also: Why don't you leave a note in our guestbook?

This year, however, we slightly changed the appaerance of our report: Instead of sub dividing our research activities into chapters we now cluster the activities into the different research groups as shown on our homepage. We hope that you can accustom to this new style.


Modern semiconductor technology nowadays combines more than ten million different transistors on a single chip barely as big as a thumbnail to form an extraordinary complex and sophisticated circuit. Following Moore's law, this very large scale integration will proceed over roughly the next ten years until a single element on a chip will be scaled down to less than about 50 nm. This typical dimension of a single device, however, represents a barrier, beyond which the basic operation of an electronic device starts to be based on fundamentally different mechanisms as compared to the conventional ones.

In a classical silicon MOSFET, for example, the principle of operation is based upon the statistical motion of about 10'000 electrons per square micron, whose number may be varied by an external electrode via electric fields. This movement takes place close to the relatively rough silicon/silicon dioxide interface and is described by diffusive processes, similar to the Brown's motion of molecules.

If, however, the dimension of a device becomes comparable or even smaller than the typical distance between two scattering events, the electrons start to move ballistically, like the balls on a billiard table. Moreover, at these small sizes, the number of electrons within a single device starts to approach one. For even smaller devices, their size becomes comparable to the wavelength of the electrons themselves - typically some ten nanometers in this case: The description of the electrons behaving like little charged spheres starts to fail and to require for a quantum mechanical formulation of the device.

In our group, we investigate the electronic, electrooptical, and electromechanical properties of specially tailored semiconductor structures with typical dimensions of the order or less than 100 nm. Recently, we also started to process and investigate mechanical systems like resonators and oscillators on the nanometer scale. Our goal is the detailed understanding of the new physical phenomena associated with a dramatic reduction of size, to explore new grounds for future device applications, and to be prepared for the day when nano-electronics will take over the role of micro-electronics and micro or nano-mechanics will open new routes to the tiny ultra small universe!

- to boldly go where no person has ever gone before !

The research in our group is based on three fundamental prerequisites :

Starting from suited semiconductor layered systems, we first have to prepare the desired structures with lateral nanometer size dimensions. We use and develop different nanotechnologies that enable us to scale down the size of our structures to the size of the electronic wavelength. For this purpose, our nanotechnology labs are located in a dust free cleanroom area containing modern semiconductor processing equipment.

As we're always trying to be internationally competitive, we set up a large number of international co-operations with partners being specialized in the epitaxial growth of our high quality starting material. Meanwhile, our nanotechnological techniques are also transferred to different disciplines of leading edge research resulting in newly developed collaborations with highly qualified specialists in x-ray analysis, polymer physics and biophysics.

Secondly, we constantly develop and apply sensitive experimental techniques which enable us to chararcterize and to investigate the electronic and optical properties of our nanometer scale samples over the whole spectral range starting from DC over the microwave and infrared regime, the visible spectrum up to UV. At the same time, we are equipped with facilities allowing fo extremely low temperatures and high magnetic fields - invaluable tools for the detailed understanding of the quantum mechanic phenomena in our devices.

A third prerequisite for our research is a detailed and fundamental theoretical analysis and understanding of nanophysics. Together with many theoretical groups and in a very fruitful atmosphere of collaboration, we try to develop new theories and techniques helping us to understand or to predict the many fascinating effects that we are constantly facing. This is in particular important, as we are not studying systems already existing in nature but try to artificially tailor small pieces of this nature to behave in a desired fashion.

Summary of the different research topics

Prof. Dr. Jörg P. Kotthaus
Head of the group

Dr. Robert Blick: Nanomechanics, Quantum Dots, Ion Channels .. Dr. Robert Blick
Nanomechanics, Quantum Dots, Ion Channels ..

Prof. Dr. Khaled Karraï
Near Field Optics
Scanning probe microscopy

Prof. Dr. Khaled Karraï: Near Field Optics

Dr. Bert Lorenz
Silicon technology
EBD materials

PD Dr. Achim Wixforth
Surface Acoustic Waves
FTIR Spectroscopy

PD Dr. Axel Lorke
Far Infrared Spectroscopy
Self assembled nonostructures
Semiconductor-cell hybrids