Application of positron annihilation techniques in semiconductor studies

Grzegorz P. Karwasz 1,3Bogdan Kusz 2Roberto S. Brusa 1Antonio Zecca 1

1. Dipartimento di Fisica, Universita' di Trento, via Sommarive, 14, Trento 38050, Italy
2. Politechnika Gdańska, Instytut Fizyki, Narutowicza 11/12, Gdańsk 80-233, Poland
3. Pedagogical University of Słupsk, Institute of Physics (IF PAP), Arciszewskiego 22B, Słupsk 76-200, Poland


New, high intensity, narrow-spot positron beams open new possibilities for solid state spectroscopy. Positron annihilation techniques, being non-destructive, allowing depth profiling down to a few micrometers and detecting open-volume defects (vacancies, dislocations etc.) at single ppm concentrations constitute a valuable and complementary method, compared to other solid-state-physics studies.
We give examples of investigation in the field of semiconductors, performed with experimental techniques available at Trento University: 1) Doppler broadening of the 511 keV annihilation line method studied with a slow-positron beam facility, 2) positron life-time techniques with about 160 ps resolution, 3) Doppler-coincidence method in bulk.
Examples of applications are shown with the aim:
i)to follow the interstitial oxygen atoms dynamics and oxygen precipitates in Czochralski-type silicon at different stages of annealing using Doppler coincidence;
ii)to monitor the reduced layers and metal nanocrystals in semiconducting glasses
iii)to follow ageing processes in high-porosity, novel dielectric materials.
In particular:
i)Lowering of the coincidence parameter in Si samples annealed at 450C indicates migration of oxygen atoms from defect sites to interstitial positions. This type of annealing is a standard recipe of semiconductor industries, used for "as-grown" samples, in order to remove the electrical activity of oxygen atoms. The recipe was purely phenomenological and positron annihilation studies allow to explain it.
ii)Tracing the "valence" annihilation S-parameter allows to determine optimum thermal treatments for the desired reduced depth. Glasses are used for electron-multipliers and image-intensifiers.
iii)Ageing of high-porosity, low- ε materials, due to filling of pores by atmospheric gases. The lowering of 3- γ annihilation events indicated reductions of free-volumes inside the material. This processes is reversible.

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Presentation: invited oral at E-MRS Fall Meeting 2003, Symposium B, by Grzegorz P. Karwasz
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-07 11:46
Revised:   2009-06-08 12:55
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