The dependence of terahertz radiation on the built-in electric field in semiconductor microstructures

Abstract

The amplitudes of terahertz radiation are measured for a series of GaAs surface intrinsic-N(+) structures with various built-in surface electric fields as the bias. As the surface field is lower than the so-called "critical electric field" related with the energy difference between the Gamma to L valley of the semiconductor, the amplitude is proportional to the product of the surface field and the number of photo-excited carriers. As the surface field exceeds the critical field, the amplitude is independent of the surface field but proportional to the product of the critical field and the number of the photo-excited carriers.

Shaping the spectrum of terahertz photoconductive antenna by frequency-dependent impedance modulation

“…Despite considering log-spiral PCAs based on the LT-GaAs to showcase the potential of the proposed approach, it could also be applied to other types of photoconductors (i.e. exploiting different materials and laser pumps [16,[20][21][22][24][25][26][27][28][29]) and other antenna topology [55], as well as for modelling of the continuous-wave THz generation in the PCA [41]. The proposed approach for shaping the THz pulse spectrum can be used for a broad range of THz technology applications in condensed matter physics [3], material science [4], gas sensing [5], chemistry [6], biology and medicine [7].…”

“…• Thz pulse generation and detection in accelerating charge carriers of semiconductors, such as low-temperature grown semiconductors (LT-GaAs or LT-InGaAs) and related heterostructures [20][21][22][23], radiation-damaged semiconductors (GaAs or Si) [24,25], in ZnSe [26], GaAsBi [27] and others, using the photoconductivity [16], the photo-dember effect [28] or the built-in electric field [29]. • THz pulse generation and detection in nonlinear media, such as semiconductors (ZnTe, GaAs, GaP, InP, GaSe) [30], inorganic electrooptical crystals (LiNbO 3 , LiTaO 3 ) [31,32], organic crystals [33], and VO 2 -films undergoing metal-insulator phase transition [34], using optical rectification [35] and electrooptical effects [36].…”

Highly Accurate in Vivo Terahertz Spectroscopy of Healthy Skin: Variation of Refractive Index and Absorption Coefficient Along the Human Body

“…First, we ensured that during the experiment and TPS data processing we have satisfied all the demands associated with the reference window position (see Section III-C). Second, we considered the reconstructed material parameters as an initial condition to solve the direct problem [see (10)- (12)] and to obtain the waveform models. White Gaussian noise, which is inherent to the experimental waveforms, was added to the models of the TPS waveforms, the TPS inverse problem was solved (2), and the error bars were calculated via (14).…”

“…The thickness of the reference window is mm, and the THz material parameters of the reference window represent the crystalline quartz [67]. A time-domain representation of the waveforms is obtained via the inverse Fourier transform (12) where stands for the inverse Fourier transform operator. Equations (10)-(12) allow us to solve the direct problem, namely, to simulate the backscattering of the THz pulse and to estimate the waveforms.…”

“…To study the stability of the inverse problem solution, we introduce the negative factors of reconstruction (digital noise in the TPS waveforms and translational and angular fluctuations of the reference window position) at the stage of the direct problem solution [see (10)- (12)], and then obtain the distorted TPS waveforms and solve the inverse problem (2). The errors of the THz refractive index and absorption coefficient reconstruction are calculated via a comparison of the initial, , and the reconstructed, , parameters.…”