Ultrafast dynamics in photoexcited valence-band states of Si studied by time- and angle-resolved photoemission spectroscopy of bulk direct transitions

We identify direct-transition photoemission peaks from the bulk valence bands of Si in energy- and momentum-resolved photoemission from Si(111)-(7×7) using polarized 6-eV laser light. Time-resolved study of spectral line shapes of the peaks under interband excitation by 2-eV femtosecond-laser pulses shows the ultrafast transient spectral-width broadening and its recovery associated with a low-energy peak shift. The changes reveal the dynamics of screening effects by electron-hole plasma, hot-hole relaxation, and band renormalization in photoexcited Si, showing strong many-body effects in relaxation at excitation density less than 1018cm-3.