Investigation of ultrafast photothermal surface expansion and diffusivity in GaAs via laser-induced dynamic gratings
This thesis details the first direct ultrafast measurements of the dynamic thermal expansion of a surface and the temperature dependent surface thermal diffusivity using a two-color reflection transient grating technique. Studies were performed on p-type, n-type, and undoped GaAs(100) samples over a wide range of temperatures. By utilizing a 90 fs ultraviolet probe with visible excitation beams, the effects of interband saturation and carrier dynamics become negligible; thus lattice expansion due to heating and subsequent contraction caused by cooling provided the dominant influence on the probe. At room temperature a rise due to thermal expansion was observed, corresponding to a maximum net displacement of {approximately} 1 {Angstrom} at 32 ps. The diffracted signal was composed of two components, thermal expansion of the surface and heat flow away from the surface, thus allowing a determination of the rate of expansion as well as the surface thermal diffusivity, D{sub S}. By varying the fringe spacing of the grating, this technique has the potential to separate the signal contributions to the expansion of the lattice in the perpendicular and parallel directions. In the data presented here a large fringe spacing was used, thus the dominant contribution to the rising edge of the signal was expansion perpendicular to the surface. Comparison of he results with a straightforward thermal model yields good agreement over a range of temperatures (20--300{degrees}K). Values for D{sub S} in GaAs were measured and found to be in reasonable agreement with bulk values above 50{degrees}K. Below 50{degrees}K, D{sub S} were determined to be up to an order of magnitude slower than the bulk diffusivity due to increased phonon boundary scattering. The applicability and advantages of the TG technique for studying photothermal and photoacoustic phenomena are discussed.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE; USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 7276846
- Report Number(s):
- LBL-32383; ON: DE92017112
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Investigation of ultrafast photothermal surface expansion and diffusivity in GaAs via laser-induced dynamic gratings
Dynamics of surface thermal expansion and diffusivity using two-color reflection transient gratings
Related Subjects
36 MATERIALS SCIENCE
GALLIUM ARSENIDES
SURFACE PROPERTIES
GRATINGS
HABIT PLANES
HEAT FLOW
LASERS
PHOTOACOUSTIC EFFECT
PHYSICAL RADIATION EFFECTS
THERMAL DIFFUSIVITY
THERMAL EXPANSION
TIME RESOLUTION
ARSENIC COMPOUNDS
ARSENIDES
EXPANSION
GALLIUM COMPOUNDS
PHYSICAL PROPERTIES
PNICTIDES
RADIATION EFFECTS
RESOLUTION
THERMODYNAMIC PROPERTIES
TIMING PROPERTIES
664200* - Spectra of Atoms & Molecules & their Interactions with Photons- (1992-)
360606 - Other Materials- Physical Properties- (1992-)