Charge carrier effects in free standing Si membranes investigated by linear and second harmonic optical techniques

Ndebeka, Wilfrid Innocent (2016-12)

Thesis (PhD)--Stellenbosch University, 2016

Thesis

ENGLISH ABSTRACT : Silicon (Si) based materials have been of technological importance throughout the years and today silicon remains a leading material in microelectronics industries. The silicon/silicon dioxide (Si/SiO2) interface has been one of the most studied systems in the realms of material and condensed matter physics. Despite the great outpouring research and huge technological success, there has been little effort to construct a comprehensive, unified microphysical model of the Si/SiO2 interface. The optical properties, both linear and nonlinear, of the interface region are of interest since they vary considerably from those of the adjacent bulk phases. Second harmonic generation is used as a versatile tool to investigate surfaces and buried interfaces of centrosymmetric materials such as Si. Specifically, the electric field induced second harmonic (EFISH) generation process is used as a valuable technique to investigate the mechanisms of charge transfer and trap generation and population, both by electrons and holes being pumped across the interface. In this work, the transmission of the fundamental laser beam (90 fs pulse trains at 80MHz repetition rate, 800 nm) through 10 m to 30 m thick silicon (Si) membranes as well as simultaneous measurements of the electric field induced second harmonic (EFISH) generated in reflection from and transmission through the Si membranes are reported for the first time. The transmission of the laser power through Si membranes, irradiated at an incident angle of 45 , shows an increase with increased power, then reaches a maximum, and finally continues to decrease considerably as the incident power is increased. A similar behavior is observed with the EFISH signals in transmission of the Si membranes. The nonlinear behavior of the fundamental transmitted signal is attributed to free charge carrier absorption (FCA) in Si. The experimental setup and these results are discussed in this thesis.

AFRIKAANSE OPSOMMING : Silikon (Si) gebaseerde materiale is reeds vir jar van tegnologiese belang en vandag Si steeds ’n prominente materiaal in die mikroëlektronika nywerheid. Die silikon/silikondioksied (Si/SiO2) skeidingsvlak is een van die mees bestudeerde stelsels in die navorsingsveld van materiaal- en vastetoestand- Fisika. Ten spyte van die omvangryke navorsing en groot tegnolgiese sukses , is daar nog min werk gedoen om’n omvattende, verenigde fisiese model op die mikroskopiese skaal van die Si/SiO2 skeidingsvlak te ontwikkel. Die optiese eienskappe , sowel lineêre en nie-lineêre , van die skeidingsvlak-gebied is van belang aangesien die oorgansgebied se eienskappe beduidend verskil van dié van aangrensende uniforme fases. Tweede harmoniek generering word gebruik as ’n veelsydige tegniek om oppervlaktes en interne skeidingsvlakke van sentrosimmetriese materiale soos Si te ondersoek. Die elektriese veld geïnduseerde tweede harmoniek (EFISH) genereringsproses word spesifiek gebruik as ’n veelsydige tegniek om die meganismes van ladingsoordrag, ladingsval-generering en die bevolking van ladingsvalle te ondersoek-, deur beide elektrone en holtes oor die skeidingsvlak te pomp. In hierdie werk word vir die eerste keer verslag gedoen van meting van die transmissie van die fundamentele laserbundel (90 fs pulse teen ’n herhalingstempo van 80 MHz, 800 nm) deur 10 mikrometer tot 30 mikrometer dik silikon (Si) membrane, sowel as gelyktydige meting van die electriese veld geïnduseerde tweede harmoniek (EFISH) wat gegenereer word in refleksie van en transmissie deur die Si membrane. Die deurgelate fundamentele laserdrywing deur Si membrane, teen 45 grade invalshoek, too ’n toename met verhoogde drywing van die invallende lig, dan ’n maksimum, en verminder daarna aansienlik met verdere toename in drywing van die invallende lig. Die nie-lineêre gedrag van die fundamentele sein in transmissie word toegeskryf aan vrye ladingsdraer-absorpsie (FCA) in Si. Die eksperimentele opstelling en hierdie resultate sal in hierdie proefskrif bespreek word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100120
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