Ultrafast Carrier Dynamics Measured by the Transient Change in the Reflectance of InP and GaAs Film
- Helmholtz Association of German Research Centers, Dresden (Germany)
Advancements in microfabrication techniques and thin film growth have led to complex integrated photonic devices, also known as optoelectronics. The performance of these devices relies upon precise control of the band gap and optical characteristics of the thin film structures, as well as a fundamental understanding of the photoexcited carrier thermalization, relaxation, and recombination processes. An optical pump-probe technique has been developed to measure the transient behavior of these processes on a sub-picosecond timescale. This method relies upon the generation of hot carriers by theabsorption of an intense ultrashort laser pulse (~ 135 fs). The transient changes in reflectance due to the pump pulse excitation are monitored using a weaker probe pulse. Control of the relative time delay between the pump and probe pulses allows for temporal measurements with resolution limited only by the pulse width. The transient change in reflectance is the result of a transient change in the carrier distribution. Observation of the reflectance response of indium phosphide (InP) and gallium arsenide (GaAs) films on a sub-picosecond timescale allows for detailed examination of thermalization and relaxation processes of the excited carriers. Longer timescales (> 100 ps) are useful for correlating the transient reflectance response to slower processes such as the diffusion and recombination of the photoexcited carriers. This research investigates the transient hot carrier processes in several InP and GaAs based films similar to those commonly used in optoelectronics. This technique is especially important as it provides a non-destructive means of evaluating these materials; whereas much of the research performed in this field has relied upon the measurement of transient changes in the transmission of transparent films. The process of preparing films that are transparent renders them unusable in functioning devices. This research should not only extend the understanding of the dynamics of the hot carrier distributions in these materials, but also provide the basis for future development of better diagnostic instruments for the non-destructive evaluation of these important materials. A theoretical model describing the change in reflectance due to the photoexcited hot carrier distribution has also been developed. By applying this model to the experimental results, several important material parameters such as the electron-phonon scattering time and the rates for diffusion and several recombination processes are determined. These values are compared with those reported for similar materials, and the validity of the results is discussed. A complete description of the experimental technique as well as the theoretical reflectance model is presented.
- Research Organization:
- Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- AC05-84ER40150
- OSTI ID:
- 920104
- Report Number(s):
- JLAB-FEL-05-480; DOE/ER/40150-4395; TRN: US200822%%675
- Country of Publication:
- United States
- Language:
- English
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