Investigation of recombination parameters in silicon structures by infrared and microwave transient absorption techniques

Abstract

Contactless techniques of infrared and microwave absorption by free carriers for the monitoring of silicon structures are described. Theoretical principles of photoconductivity decay analysis and methodology for the determination of recombination parameters are given for both homogeneous and non-homogeneous excess carrier generation. Different approximations (the methods of decay amplitude - asymptotic lifetime analysis, the simulation of the whole decay curve, the variation of effective lifetime with wafer thickness and the asymptotic lifetime measurement for stepwise varying parameters in layered structure) corresponding to real experimental conditions for various structures and treatments of materials, which are important for microelectronics, are discussed. The determined recombination parameters in the range of bulk lifetime , velocity of surface recombination and diffusion coefficient are illustrated for Si wafers obtained by various doping and preparation processes. The necessity to consider carrier trapping effects and nonlinear recombination processes is demonstrated by the analysis of experimental results obtained at different excitation levels for carrier concentrations in the range . The possibility of extracting the parameters of the traps (with activation energy values , and ) from the temperature-dependent asymptotic carrier lifetime measurements is illustrated for neutron transmutation doped wafers.