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We discuss the generation mechanism of THz radiation and acoustic phonon pulse wave under ultra short pulse excitations in GaN-based light emitting diode (LED) structures containing InGaN/GaN multiple quantum wells. In order to understand the role of piezoelectricity in the THz radiation and acoustic phonon pulse wave generations, an external field...
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... the THz radiation can last longer than the carrier lifetime measured either by time-resolved photoluminescence or by pump-probe experiments. This explains that the THz radiation can last up to 40 ps (see Fig. 1) regardless of the reverse voltage. The excitation energy dependence of the pump-probe signal and the THz signal at 20 V is given in Fig. 6. Pump-probe signal increases with increasing excitation energy up to 3.3 eV, but decreases above it. The increase below 3.3 eV is mainly due to the increased absorption coefficient and the corresponding increase of photocarriers with increasing excitation energy. Above the photon energy of 3.3 eV, the absorption at the p-GaN layer near ...
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Citations
We report for the first time a carbon-doped gallium nitride based large aperture photoconductive switch grown on the sapphire substrate to generate high power sub-THz waves. The estimated THz wave energy was about 1.5 pJ/pulse when this device was pumped by a 266 nm wavelength femtosecond laser operating at 1 kHz pulse rate with the average power of 20 mW under the dc bias voltage of 110 V. The terahertz time domain spectroscopy was performed using a low temperature grown gallium arsenide photoconductive switch detector and the frequency spectrum was found to be in the 0.1-0.2 THz regime.
We demonstrate the generation of picosecond acoustic pulses using a piezoelectric-semiconductor-based p‐n junction structure. This p‐n junction picosecond ultrasonic experiment confirms that the piezoelectric effect dominates the thermal expansion and deformation-potential coupling in the generation of picosecond acoustic pulses. The characteristics of the p‐n initiated acoustic pulses are determined by the width and the field strength inside the depletion region. Our study indicates the future possibility to electrically control the acoustic pulse characteristics if we could apply an external bias to modulate the depletion region width.
