Probing carrier and phonon transport in semiconductors all at once through frequency-domain photoreflectance

Semiconductor devices favor high carrier mobility for reduced Joule heating and high thermal conductivity for rapid heat dissipation. The ability to accurately characterize the motion of charge carriers and heat carriers is necessary to improve the performance of electronic devices. However, the conventional approaches of measuring carrier mobility and thermal conductivity require separate and independent measurement techniques. These techniques often involve invasive probing, such as depositing thin metal films on the sample as Ohmic contacts for characterizing electrical transport or as optical transducers for characterizing thermal transport, which becomes more cumbersome as the geometry of the semiconductor devices becomes small and complicated. Here we demonstrate a noncontact frequency-domain pumpprobe method that requires no sample pretreatment to simultaneously probe carrier and phonon transport. We find that the optical reflectance depends on both excess carriers and phonons in response to exposure to a modulated continuous-wave pump laser source. By modeling the ambipolar diffusion of photoinduced excess carriers, energy transfer between electrons and phonons, and phonon diffusion, we are able to extract temperature-dependent electrical and thermal transport coefficients in Si, Ge, SiGe, and GaAs. The continuous-wave pump and probe lasers enable a more efficient and compact experimental setup for the assessment of electrical transport than conventional pulsed-laser methods. Our approach provides a convenient and accurate platform for the study of the charge transport and energy dissipation in semiconductors.