Temperature dependence of carrier relaxation time in gallium phosphide evaluated by photoemission measurements

For understanding of carrier behavior in semiconductors, it is important to measure the carrier relaxation time. In the present study, the relaxation times of inter-valley transition from the Γ valley to the X valley in GaP were evaluated by near-band-gap photoemission spectroscopy of electrons emitted from a surface with a negative electron affinity state. In the energy distribution curves, two peaks, which originate from the electron population accumulated in the Γ valley and the X valley, were observed. From the temperature dependence of the energy of these two peaks, we could successfully evaluate the temperature dependence of the energies of the Γ valley and the X valley. Furthermore, the relaxation times of the inter-valley transition from the Γ valley to the X valley were estimated from the ratio of the electron concentration of the Γ valley and the X valley. The values of the relaxation time are good agreement with the previous studies. These results indicate that the near-band-gap photoemission spectroscopy can directly investigate conduction electrons and also evaluate the carrier dynamics in semiconductor.