Femtosecond laser diagnostics of thin films, surfaces and interfaces
An overview is given of optical second harmonic generation (SHG) using femtosecond laser pulses to analyse technologically important crystalline materials. The principle of SHG is briefly explained and a typical experimental setup for SHG is outlined. The second harmonic (SH) measurements performed in prototype compound semiconductors reveal the crystalline structure and orientation of monocrystalline SiC, polycrystalline ZnO, and the ternary compound, PbxCd1-xTe, showing the segregation of a Pb-and a Cd-rich phase. Furthermore, SHG can selectively probe the Si/SiO2 interface and the build-up of its electric field induced by laser-activated charge carrier separation. The examples presented demonstrate that SHG is a versatile technique to probe the structural and electronic properties of crystalline materials and particularly surfaces and interfaces.