Frequency Shift of Terahertz Electromagnetic Waves Originating from Sub-Picosecond-Range Carrier Transport in Undoped GaAs/n-Type GaAs Epitaxial Layer Structures

Abstract

We study the level spacing distribution p(s) in the spectrum of random networks. According to our numerical results, the shape of p(s) in the Erdős-Rényi (E-R) random graph is determined by the average degree k and p(s) undergoes a dramatic change when k is varied around the critical point of the percolation transition, k = 1. When k 1, the p(s) is described by the statistics of the Gaussian orthogonal ensemble (GOE), one of the major statistical ensembles in Random Matrix Theory, whereas at k = 1 it follows the Poisson level spacing distribution. Closely above the critical point, p(s) can be described in terms of an intermediate distribution between Poisson and the GOE, the Brodydistribution. Furthermore, below the critical point p(s) can be given with the help of the regularized Gamma-function. Motivated by these results, we analyse the behaviour of p(s) in real networks such as the internet, a word association network and a protein-protein interaction network as well. When the giant component of these networks is destroyed in a node deletion process simulating the networks subjected to intentional attack, their level spacing distribution undergoes a similar transition to that of the E-R graph.

Detection of a Coherent Longitudinal Optical Phonon in a GaAs Buffer Layer Optically Covered with a GaSb Top Epitaxial Layer Using Terahertz Spectroscopy

“…In fact, the intense THz emission from the coherent GaAs LO phonon is also observed with the photoconductive dipole antenna in GaAs/AlAs multiple quantum wells 6 and undoped GaAs/n-type GaAs epitaxial structures. 7 We also performed the fitting to the THz waveform with use of two damped sinusoidal functions in order to confirm the appearance of the two LO-phonon bands in the Fourier power spectrum shown in Fig. 2(b).…”

“…1,2 The above-mentioned progress enables the detection of the THz electromagnetic waves from coherent phonons. [3][4][5][6][7] THz spectroscopy gives an interesting issue on the generation of the coherent phonons. In the conventional Raman scattering process, phonons are generated directly by the excitation light.…”

Terahertz Electromagnetic Waves from Semiconductor Epitaxial Layer Structures: Small Energy Phenomena with a Large Amount of Information

“…The above-mentioned epitaxial layer structure design is based on the fundamental semiconductor physics, so that the results demonstrated here contain a large amount of information on ultrafast carrier dynamics. We organize the present chapter based on our recent works (Takeuchi et al, 2008;2009;2010). In Section 2, we review the current status of terahertz-wave spectroscopy, and discuss the hidden problems.…”

Emission of the terahertz electromagnetic wave from coherent longitudinal optical phonons in a GaAs buffer layer optically masked by a GaSb top epitaxial layer

“…[2][3][4][5][6][7] In contrast, terahertz wave spectroscopy has a potential to directly detect the signals of the coherent LO phonons as terahertz electromagnetic waves. We note that the terahertz waves from the coherent LO phonons have been investigated by various groups; [8][9][10][11] however, the probing of those in the optically masked layer has been neglected. The scenario described above provides us an important aspect of the generation mechanism of the terahertz waves from the coherent LO phonons, which will make advances in terahertz science and technology.…”