Investigation of THz Radiation from Longitudinal Optical Phonon- Plasmon Coupling in p-i-n Diodes

Abstract

Terahertz radiation (THz) in infrared domain at room temperature has many applications in science and technology, especially in the technology of analyzing and processing image. This paper introduces a relatively simple method to investigate the Terahertz radiation from the coupling of Longitudinal Optical (LO) phonon and coherent plasmon in p-i-n diode structure. The frequency spectra are found from the Fast Fourier Transform (FFT) of the voltage between two neighboring points in the insulating region of this diode. Numerical calculations have been applied for GaAs semiconductor device with the photo-excited carrier density ranging from 17 1.0×10 cm-3 to 18 3.0×10 cm-3 and the insulating layer size of 500 nm. In order to study of the coupling of LO phonon in p-i-n diode based on the EMC simulations, the equation of density vibration is solved simultaneously with the simulation of carrier dynamics, this is performed with spatial resolution of 1A° and time resolution of 0.20 fs . We solve the Poisson’s equation to derive the potentials along the x-axis in both cases with and without taking into account the coupling. The frequency spectrum derived from the FFT of the voltage of two layers separated by a distance 10 nm in insulating layer (i). The frequency spectrum derived from the Fourier transform of the voltage between two neighboring points with and without LO phonon–plasmon coupling is shown. We can easily observe the existence of the modes which are close to the frequency values of bulk semiconductor. It should be noted that, our calculations are reasonable agreement with experiments measured by the Ibanez et al in Phys. Rev. B 69 (7), 075314 (2004). In this paper, we present a relatively simple approach to investigate the THz radiation from the coupling of LO phonon-plasmon in p-i-n diode structure by taking the FFT of the voltage of two neighboring points in insulating semiconductor region. The voltage is calculated through the electric potentials which relate to the charge density via Poisson’s equation. Numerical calculations have been performed for GaAs semiconductor device with carrier density ranging from 17 1.0×10 cm-3 to 18 3.0×10 cm-3. Our simulations calculations show that with appropriate photoexcited carrier density, two strong coupling LO phonon-plasmon coherent modes are appear.