The steady and transient photoconductivity, and related phenomena in the neutron irradiated Si.

1. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 The steady and transient photoconductivity, and related phenomena in the neutron irradiated Si. J.Vaitkus, E.Gaubas, A.Kadys, V.Kalendra, V.Kazukauskas, A.Mekys, J.Storasta, E.Zasinas Vilnius University, Institute of Materials Science and Applied Research

2. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Outline: A few general words about the photoconductivity & related transport phenomena The results: general data the peculiarities Attempts to conclude

3. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Definition: If the sample is uniform, then the chosen effects: photoconductivity, light induced transient gratings, Hall and photo-Hall effects, magnetoresistance effects allow to characterize the behavior of free carriers and the local levels in the sample and their parameters . The inhomogegenities differently influence these effects, therefore the complex application gives a possibility to recognize what happens in the sample after a certain treatment.

4. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Photoconductivity Photoconductivity spectra allows to identify the deep level and characterize a role of electron-phonon interaction in its environment.

5. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Spectra in irradiated Si

6. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Transitions

7. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Intrinsic photoconductivity

8. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Si 3 1016 cm-2 and summary

9. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Steady state lifetime dependence on fluence

10. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Extrinsic photoconductivity

11. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Transient photoconductivity (TP) Light pulse excitation TP can be measured by: DC circuit (contact problems) Microwave technique Free carrier absorption (~ non-sensitive to mobility) Transient gratings: measure free carrier concentration profile amplitude, i.e. allows to measure concentration decay law and diffusitivity, separately. TP gives information about recombination cannels and traps

12. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Transient gratings

13. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Transient gratings

14. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Transport phenomena: Hall, photo-Hall, magnetoresistance effects Comparison Hall and magnetoresistance effects � a role of inhomogeneity Temperature dependence of mobility � depends on scattering mechanism

15. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Hall mobility and magnetoresistance vs temperature

16. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Hall mobility, annealing, excitation effects

17. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Conductivity vs T

18. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Photoconductivity decay

19. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Compare the dependences on fluence the data measured by photoconductivity and by microwaves technique

20. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Conclusions:

21. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Thanks for Your attention !!!

22. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 The peculiarities of dark conductivity, photoconductivity and other transport phenomena were investigated in the neutron irradiated Si. The photoconductivity mechanism, observed deep levels and the effects related to the nano- and micro- defects are discussed. At low temperature (18K) The measurement pf photoconductivity spectral dependence in the high absorption region shows the decrease of photoconductivity related with an increase of recombination at the surface, but the comparison with a standard surface velocity model show that the main recombination is going not at the surface, but in the layer near to surface. Probably there is different doping of the bulk and the layer near to surface. The photoconductivity at the absorption edge linearly depends on the intensity of light that shows that in the investigated range of intensities on type of recombination canters plays the main role. The steady state lifetime depends as a square root on the fluence. The microwave date showed its linear dependence, therefore it is necessary to predict the more complicated process of recombination. It could be proposed that this peculiarity is related with the very fast recombination process observed in the measurements with the picosecond resolution. The extrinsic photoconductivity shows two different regions: on � clearly expressed impurity photoconductivity band from the level at 0,8-0,9 eV that at low fluence linearly depends on the fluence and saturate at high fluence. The second band (level ~0,5-0,6 eV) is caused by the induced photoconductivity by capture of carriers generated from the deeper level or the intrinsic photogeneration. These levels can be related with clusters because they demonstrate the accumulation effect that cause the partial compensation of the deeper level (the impurity photoconductivity becomes linear to the excitation). Near to the room temperature and down to the liquid nitrogen temperature. The measurement of Hall effect mobility by Hall effect and by magnetoresistance shows more or less the same data in the lowest fluence sample. For higher fluences the difference becomes high that can be explained only by model of inhomogeneous sample and percolation type of conductivity. The data of photo-Hall effect support this model. The heating cycle up to 80 C shows the significant change of the percolation and the important role of the overlap of the space charge regions in the bulk of sample. The clusters with the effective charge of a few electron charge was evaluated.

23. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Si bandgap f(T)_

24. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06

25. J.Vaitkus et al., WOEDAN Workshop, Vilnius, 2007.06.06 Dark current vs T