INVESTIGATION OF RECOMBINATION PARAMETERS IN SILICON STRUCTURES BY INFRARED AND MICROWAVE TRANSIENT ABSORPTION TECHNIQUES

Contactless techniques of infrared and microwave absorption by free ca rriers for the monitoring of silicon structures are described. Theoret ical principles of photoconductivity decay analysis and methodology fo r the determination of recombination parameters are given for both hom ogeneous and non-homogeneous excess carrier generation. Different appr oximations (the methods of decay amplitude-asymptotic lifetime analysi s, 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 t o real experimental conditions for various structures and treatments o f materials, which are important for microelectronics, are discussed. The determined recombination parameters in the range of bulk lifetime 0.0006-230 mu s, velocity Of surface recombination 600-5 x 10(4) cm s( -1) and diffusion coefficient 0.015-18 cm(2) s(-1) are illustrated for Si wafers obtained by various doping and preparation processes. The n ecessity to consider carrier trapping effects and nonlinear recombinat ion processes is demonstrated by the analysis of experimental results obtained at different excitation levels for carrier concentrations in the range 10(13)-10(18) cm(-3). The possibility of extracting the para meters of the traps (with activation energy values 0.16 +/- 0.02 eV, 0 .20 +/- 0.02 eV and 0.28 +/- 0.04 eV) from the temperature-dependent a symptotic carrier lifetime measurements is illustrated for neutron tra nsmutation doped wafers.