Laplace Deep Level Transient Spectroscopy is used to study electrically active impurities and defects in semiconductors. It has a higher sensitivity than almost any other technique (in 20 Ohmcm silicon it can detect impurities at a concentration of one part in a million million) and has sufficiently high energy resolution (a few meV) to reveal information on the impurity’s local environment such as stress or atomic siting. The invention of the experimental technique of Laplace DLTS was awarded the UK National Physical Laboratory prize for measurement in 1993 and a Royal Academy of Engineering Foresight Award in 1997. It was subsequently developed within several scientific projects funded by the European Union, the Polish Ministry of Science and Higher Education and the Foundation for Polish Science in Poland, and by the Engineering and Physical Sciences Research Council in the United Kingdom.

The experimental techniques were developed at the Institute of Physics Polish Academy of Sciences in Warsaw and at the Microelectronics and Nanostructure Group, School of Electrical and Electronic Engineering at The University of Manchester. Work is still in progress to make the technique easy to use and apply the analytical techniques to other branches of science.

At the heart of the method are mathematical routines which convert the recorded relaxation process (measured as a capacitance or current transient) from the time domain into a spectrum of time constants (in the case shown electron emission rates) in the frequency domain.

The implementation of Laplace Deep Level Spectroscopy increases the energy resolution of conventional DLTS by an order of magnitude and makes it possible to observe effects and processes which are impossible to see with the usual methods. Two examples are shown below but go to the pages on Key Results and on LDLTS Literature sections for more details.

On the left-hand side. Uniaxial stress induced splitting of the Laplace DLTS peak related to the bond-centred hydrogen in silicon is shown. The splitting pattern indicates the trigonal symmetry of the defect.. Phys. Rev. B, 65, 075205, (2002), PDF (90kB)

On the right-hand side. The appearance of the alloy splitting pattern observed for the gold acceptor state in silicon-germanium alloys. Phys. Rev. Lett., 83, 4582 (1999); Phys. Rev. B, 63, 235309 (2001)