Semiconductor chronotomography: A lifetime demultiplexing and imaging method for revealing hidden carrier loss mechanisms in electronic solids (invited)

The concept of semiconductor chronotomography (CTG) is introduced as a scanning adaptive frequency gate, a process that significantly enhances radiative [photocarrier radiometry (PCR) and its camera imaging extension, lock-in carrierography (LIC)] or non-radiative (photothermal radiometry and its camera imaging extension, lock-in thermography) signal responses to the presence of multiple free-carrier lifetime limiting mechanisms. When in a laser photoexcitation modulation frequency scan, the free-carrier decay rate matches/lies within the gatewidth between two adaptive successive modulation frequencies, CTG yields signal extrema related to resonances with free-carrier decay or recombination rates. CTG was successfully applied to the investigation of multiple lifetimes in p- and n-type Si wafers and mono- and multicrystalline solar cells using homodyne and heterodyne PCR and LIC modalities. The statistical distribution of relaxation times τ and the product f(τ) × τ, where f(τ) is the probability of occurrence of lifetime τ, are important CTG outputs: the former reveals the impact of each lifetime, while the latter weighs the lifetime with the relative probability of its occurrence. In summary, CTG in conjunction with PCR is a highly sensitive resonant rate modality. Its high sensitivity reveals multiple lifetime distributions, crucially short lifetimes otherwise hidden below much longer carrier recombination lifetimes.