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Si/SiO2 interface is a technologically relevant interface as it is used in microelectronics as the gate between the drain and source of most metal-oxide semiconductor field effect transistors. The project involves investigation of native Si/SiO2 of micro and nanostructured silicon materials using optical second harmonic generation (SHG). Due to their novel size and dimensionality the electrical and physical properties of these materials may differ from bulk materials. A mode-locked femtosecond laser is tightly focused on prepared silicon samples to generate high intensities sufficient to induce SHG at the interface. The temporal evolution of the SH signal measured in reflection from the interface is related to charge dynamics across the interface hence can give an insight of the electrical properties of the materials. We have demonstrated SHG in silicon microstructures and silicon nanowires in reflection. Transmission SHG for free-standing silicon micromembranes is being investigated. The project has the potential of investigating carrier dynamics of ultrafast pump-probe laser excitation in semiconductor heterostructures.

Past work also included studies relating to non-centrosymmetric materials, such as SiC thin films, ZnO thin films and bulk material and Pb(x)Cd(1-x)Te ternary alloys. These studies focused on determining the crystalline quality and growth orientation of the samples. The specific growth method (PLD, MOCVD, etc.) could also be characterized in this fashion.

Second Harmonic Generation Lab

The group:

  • Researchers: Prof. EG Rohwer, Prof H Schwoerer, Dr. CM Steenkamp
  • Collaborators: Prof. H Stafast, IPHT, Jena , Germany .
  • Current students: Mr. GP Nyamuda (PhD)
  • Graduated students: Dr. T Scheidt (PhD 2006), Dr. P Neethling (PhD, 2008), Mnr. G Bosman (MSc 2008)

Selected publications:

(for complete list of publications see Publications)

Papers

  • Neethling, P. H.; Rohwer, E. G.; von Bergmann, H. M. & Stafast, H. (2008), 'Analysis of ZnO thin films by second harmonic generation', physica status solidi (c) 5 (2), 552--554.

  • Scheidt, T.; Rohwer, E.; Neethling, P.; von Bergmann, H. & Stafast, H. (2008), 'Ionization and shielding of interface states in native p+ - Si/SiO2 probed by electric field induced second harmonic (EFISH) generation', Journal of Applied Physics 104 , 083712-1--083712-8.

  • Scheidt, T.; Rohwer, E. G.; von Bergmann, H. M. & Stafast, H. (2006), 'Ultraviolet pulse laser induced modifications of native silicon/silica interfaces analyzed by optical second harmonic generation', Journal of Applied Physics 100 (2), 023116.

  • Scheidt, T.; Rohwer, E. G.; von Bergmann, H. M.; Saucedo, E.; Dieguez, E.; Fornaro, L. & Stafast, H. (2005), 'Optical second-harmonic imaging of PbxCd1-xTe ternary alloys', Journal of Applied Physics 97 (10), 103104.

  • Scheidt, T.; Rohwer, E.; Von Bergmann, H. & Stafast, H. (2004), 'Optical second harmonic imaging of zinc oxide thin films grown by metal organic chemical vapour deposition (MOCVD)', physica status solidi (c) 1 (9), 2243--2249.

  • Scheidt, T.; Rohwer, E. G.; von Bergmann, H. M. & Stafast, H. (2004), 'Optical second harmonic imaging: a versatile tool to investigate semiconductor surfaces and interfaces', European Physical Journal-Applied Physics 27 (1-3), 393--397.

  • Scheidt, T.; Rohwer, E. G.; von Bergmann, H. M. & Stafast, H. (2004), 'Charge-carrier dynamics and trap generation in native Si/SiO2 interfaces probed by optical second harmonic generation' , Physical Review B 69 (16), 165314.