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The 30th International Conference on Advanced Laser Technologies
N-O-7
Velocity overshoot and terahertz generation in AlxGa1-xAs/GaAs heterostructured p-i-n diodes
V. Trukhin1, I. Mustafin1, X. Fan12, V. Kalinovsky1, E. Kontrash1, K. Prudchenko1, I.
Tolkachev1 and V. Malevich34
1-Ioffe Institute, 19021, St Petersburg, Russia 2- ITMO University, 197101, St Petersburg, Russia 3- Belarusian State University of Informatics and Radioelectronics, Minsk, Belarus 4- Stepanov Institute of Physics, Belarusian Academy of Sciences, Minsk, Belarus
Main author email address: man-st@mail.ru
Fig. 1. Dependence of THz pulse amplitude and time locftion of THz pulse on the bias (tapt = 793, 860 ^m)
This paper presents the results of an experimental study of terahertz radiation generation in AlxGa1-xAs/GaAs heterostructured p-i-n diodes under femtosecond optical pulse excitation. In a study of THz radiation excited from a p-i-n diode, it was found that the maximum efficiency of THz generation is observed at a reverse bias application above 8 V and an optical excitation level up to 10 mW (a linear dependence of the THz pulse amplitude on the average power is recorded). A comparative study of THz generation in pInAs bulk semiconductor was carried out, which showed that the efficiency of THz generation in p-i-n diode is an order of magnitude higher than in p-InAs.
It was shown that the maximum pulse amplitude increases sharply as the magnitude of the reverse bias on the p-i-n diode grows, and the beginning of this growth depends on the energy of the excitation quantum of photon. Accordingly, the time position of THz pulse also changes with the change in the value of the reverse bias on the p-i-n diode, and when the value of the bias changes from positive values to the value of the diode voltage at which THz pulse amplitude begins to grow sharply, the THz pulse is delayed. With further increase in the reverse bias on the p-i-n diode, there is a reverse shift of the THz pulse on the time scale (Fig. 1). The Monte-Carlo simulation of the process of THz generation in the p-i-n diode performed by taking into account the ballistic motion of nonequilibrium carriers with the subsequent possible overshoot of the saturation speed confirmed the experimental results.
Thus, the results indicate that the mechanism of THz generation in the heterostructured p-i-n diode AlxGa1-xAs/GaAs is due to the acceleration of electrons in the electric field to a speed significantly exceeding the saturation speed at times of hundreds of femtoseconds ("velocity overshoot"), and the subsequent sharp decline associated with the intervalley transition of electrons from the T-valley. It was shown that the THz generation efficiency in the AlxGa1-xAs/GaAs heterostructure p-i-n diode at excitation levels, at which a linear dependence of the electric field amplitude on the optical radiation intensity is observed, is an order of magnitude higher than the THz generation efficiency in the p-InAs bulk semiconductor, which is now the most efficient coherent terahertz emitter [1].
[1] Adomavicius R., Urbanowicz A., Molis G., Krotkus A., Satkovskis E., Appl. Phys. Lett., vol.85, p. 2463, 2004.
'Terahertz emission from 0-lnAs due to the instantaneous polarization,"
