Femtosecond time-resolved photoemission electron microscopy for spatiotemporal imaging of photogenerated carrier dynamics in semiconductors

Journal Article · Fri Aug 15 00:00:00 EDT 2014 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.4893484· OSTI ID:22314422

Fukumoto, Keiki; Yamada, Yuki; Matsuki, Takashi; Koshihara, Shin-ya ^[1]; Onda, Ken ^[2]; Mukuta, Tatsuhiko; Tanaka, Sei-ichi ^[1]

---

1. Department of Materials Science, Tokyo Institute of Technology, Oookayama, Meguro-ku, Tokyo 152-8550 (Japan)
2. Interactive Research Center of Science, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 226-8502 (Japan)

We constructed an instrument for time-resolved photoemission electron microscopy (TR-PEEM) utilizing femtosecond (fs) laser pulses to visualize the dynamics of photogenerated electrons in semiconductors on ultrasmall and ultrafast scales. The spatial distribution of the excited electrons and their relaxation and/or recombination processes were imaged by the proposed TR-PEEM method with a spatial resolution about 100 nm and an ultrafast temporal resolution defined by the cross-correlation of the fs laser pulses (240 fs). A direct observation of the dynamical behavior of electrons on higher resistivity samples, such as semiconductors, by TR-PEEM has still been facing difficulties because of space and/or sample charging effects originating from the high photon flux of the ultrashort pulsed laser utilized for the photoemission process. Here, a regenerative amplified fs laser with a widely tunable repetition rate has been utilized, and with careful optimization of laser parameters, such as fluence and repetition rate, and consideration for carrier lifetimes, the electron dynamics in semiconductors were visualized. For demonstrating our newly developed TR-PEEM method, the photogenerated carrier lifetimes around a nanoscale defect on a GaAs surface were observed. The obtained lifetimes were on a sub-picosecond time scale, which is much shorter than the lifetimes of carriers observed in the non-defective surrounding regions. Our findings are consistent with the fact that structural defects induce mid-gap states in the forbidden band, and that the electrons captured in these states promptly relax into the ground state.

• OSTI ID: 22314422
• Journal Information: Review of Scientific Instruments, Vol. 85, Issue 8; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0034-6748
• Country of Publication: United States
• Language: English

Related Subjects

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
CARRIER LIFETIME
ELECTRON CAPTURE
ELECTRON CORRELATION
ELECTRON MICROSCOPY
EMISSION SPECTROSCOPY
GALLIUM ARSENIDES
GROUND STATES
IMAGES
LASERS
NANOSTRUCTURES
OPTIMIZATION
PHOTOEMISSION
PULSES
RECOMBINATION
RELAXATION
SEMICONDUCTOR MATERIALS
SPATIAL DISTRIBUTION
SPATIAL RESOLUTION
TIME RESOLUTION