1. Barcelona, 31 May- 2 June 20101 Contacts to High-Resistivity Semiconductors Arie Ruzin School of EE, Faculty of Engineering, Tel Aviv University, Israel

2. Barcelona, 31 May- 2 June 20102 Outline Motivation Schottky and Ohmic contacts to Low-  semiconductors Simulated results for Low- and High-  semiconductors Injecting contacts to High-  semiconductors Space Charge Limited Current Summary

3. Barcelona, 31 May- 2 June 20103 “Classic” Presentation for High-  Energy Bands (??)

4. Barcelona, 31 May- 2 June 20104 Taking Into Account Majority Carriers Only (??) Majority Carriers only ?

5. Barcelona, 31 May- 2 June 20105 Thermionic Emission (??) Thermionic emission ?

6. Barcelona, 31 May- 2 June 20106 Thermionic emission ? Thermionic Emission (??), 1.5eV barriers (?)

7. Barcelona, 31 May- 2 June 20107 Textbook Contacts (Low-  Semiconductor) EiEi SchottkyOhmicOhmic injecting? EFEF qBqB ECEC EVEV Metal Semiconductor qFqF qsqs EFEF EiEi ECEC EVEV qFqF EFEF EiEi ECEC EVEV qFqF qBqB

8. Barcelona, 31 May- 2 June 20108 Low-  CdTe Diode (N D =10 15,  B =1eV) (The diode is 1 mm long) Zoom on the front 10  m Zero Bias Low Bias Energy band structure

9. Barcelona, 31 May- 2 June 20109 Low-  CdTe Diode (N D =10 15,  B =1eV) (The diode is 1 mm long) Zoom on the front 10  m E -field profiles under bias

10. Barcelona, 31 May- 2 June 201010 Low-  CdTe Diode (N D =10 15,  B =1eV) Free carrier densities

11. Barcelona, 31 May- 2 June 201011 Low-  CdTe Diode (N D =10 15,  B =1eV) (The diode is 1 mm long) Current density Thermionic emission limited Bulk limited

12. Barcelona, 31 May- 2 June 201012 EFEF EiEi qBqB ECEC EVEV Metal Semiconductor qFqF qsqs EFEF EiEi ECEC EVEV qFqF qBqB EFEF EiEi ECEC EVEV qFqF High-  Schottky Diode (?) SchottkyOhmicOhmic injecting?

13. Barcelona, 31 May- 2 June 201013 High-  CdTe Diode (N D =10 6,  B =1eV) Zero Bias Low Bias Energy band structure

14. Barcelona, 31 May- 2 June 201014 High-  CdTe Diode (N D =10 6,  B =1eV) Free carrier densities

15. Barcelona, 31 May- 2 June 201015 High-  CdTe Diode (N D =10 6,  B =1eV) Forward and Reverse Currents

16. Barcelona, 31 May- 2 June 201016 High-  CdTe Diode (N D =10 6,  B =1.3eV) Zero Bias Low Bias Energy band structure

17. Barcelona, 31 May- 2 June 201017 High-  CdTe Diode (N D =10 6,  B =1.3eV) Free Carrier Concentration

18. Barcelona, 31 May- 2 June 201018 High-  CdTe Diode (N D =10 6,  B =1.3eV) E -Field and Potential profiles

19. Barcelona, 31 May- 2 June 201019 High-  CdTe Diode (N D =10 6,  B =1.3eV) Band Structure under forward bias ECEC EVEV

20. Barcelona, 31 May- 2 June 201020 High-  CdTe Diode (N D =10 6,  B =1.3eV) Forward and Reverse Currents Mott’s Law fit:

21. Barcelona, 31 May- 2 June 201021 High-  CdTe Diode (N D =10 6,  B =1.3eV,SRH) With SRH Recombination Without SRH Recombination Free Carrier Concentration with and without SRH

22. Barcelona, 31 May- 2 June 201022 High-  CdTe Diode (N D =10 6,  B =1.3eV,SRH) Free Carrier Concentration with and without SRH With SRH Recombination Without SRH Recombination

23. Barcelona, 31 May- 2 June 201023 High-  CdTe Diode (N D =10 6,  B =1.3eV,SRH) Currents with and without SRH

24. Barcelona, 31 May- 2 June 201024 High-  CdTe Diode (N D =10 6,  B =0.2eV) Energy band structure ECEC EVEV

25. Barcelona, 31 May- 2 June 201025 High-  CdTe Diode (N D =10 6,  B =0.2eV) Free Carrier Concentration

26. Barcelona, 31 May- 2 June 201026 High-  CdTe Diode (N D =10 6,  B =0.2eV) E -Field and Potential profiles

27. Barcelona, 31 May- 2 June 201027 High-  CdTe Diode (N D =10 6,  B =0.2eV) Band Structure

28. Barcelona, 31 May- 2 June 201028 High-  CdTe Diode (N D =10 6,  B =0.2eV) Currents Mott’s Law fit:

29. Barcelona, 31 May- 2 June 201029 Conclusions Band bending in high-  semiconductors is mainly attributed to free carrier charge – NOT dopant ions In high-  semiconductors Schottky devices thermionic emission is not the dominant forward current mechanism In case on any band bending (positive or “ negative ” barrier) the “ bulk ” resistivity is strongly affected by free carrier injection In case of significant Schottky barrier the current transport is dominated by minority carriers Space Charge Limited Current may occur both, in Schottky and “ Ohmic ” contacts (except flat-band conditions)

30. Barcelona, 31 May- 2 June 201030 Thank you