Real-time measurement of the evolution of carrier mobility in thin-film semiconductors during growth

A method which allows real-time microwave mobility measurements in thin-film semiconductors is described. Carriers mobility is determined during growth by combining two diagnostics: time-resolved microwave conductivity (TRMC) and spectroscopic ellipsometry (SE). TRMC provides the product of the number of free carriers, generated by a laser pulse, by their microwave mobility. The number of photogenerated carriers is calculated from real-time SE measurements. Therefore, the mobility of excess carriers in the growing layer can be deduced from TRMC measurements. In order to illustrate this technique, a TRMC setup has been implemented in situ together with real-time SE to analyze the growth of microcrystalline silicon (μc-Si) by radio frequency glow discharge. An increase of the average carrier mobility as a function of the film thickness is observed, which is compared with the increase of the crystalline fraction evidenced by SE.