Anisotropic excitons and their contributions to shift current transients in bulk GaAs

Abstract

Shift current transient are obtained for near band gap excitation of bulk GaAs by numerical solutions of the semiconductor Bloch equations in a basis obtained from a 14 band k·p model of the band structure. This approach provides a transparent description of the optically induced excitations in terms of interband, intersubband, and intraband excitations which enables a clear distinction between different contributions to the shift current transients and fully includes resonant as well as off-resonant processes. Using a geodesic grid in reciprocal space in our numerical solutions, we are able to include the electron-hole Coulomb attraction in combination with our anisotropic three-dimensional band structure. We obtain an excitonic absorption peak and an enhancement of the continuum absorption and demonstrate that the excitonic wave function contains a significant amount of anisotropy. Optical excitation at the excitonic resonance generates shift current transients of significant strength, however, due to the electron-hole attraction the shift distance is smaller than for above band gap excitation. We thus demonstrate that our approach is able to provide important information on the ultrafast electron dynamics on the atomic scale.

Signatures of transient Wannier-Stark localization in bulk gallium arsenide

“…As a strong THz field leads to a very rapid intraband acceleration through the entire Brillouin zone, we use in these simulations a k -independent interband dipole matrix element of eÅ, which is the average of 3 eÅ, the typical value often used for near-bandgap excitation of GaAs, and 1.5 eÅ, which is obtained for transitions at the upper band edge considering the scaling of the interband dipole matrix element. Therefore, this value is adequate and even slightly larger than the shift distance of GaAs, which amounts to approximately 2 Å at the fundamental bandgap 37 , 38 .…”

Calculation of shift current tensors in two-dimensional transition metal dichalcogenides

“…The optoelectronic response is described by the quations of motion for the reduced density matrix elements ρ λλ ′ (k) = ⟨a + λ ′ k a λk ⟩, which are also known as the semiconductor Bloch equations [17][18][19][20]…”

Photocurrents in GaAs quantum wires including excitonic effects

“…Depending on the formation mechanism, photocurrents can be classified into different types: ballistic, shift, and rectification currents. These photocurrents have been investigated in bulk materials [1][2][3][4][5][6][7][8][9][10][11][12][13][14] and quantum wells (QW) [15][16][17][18][19][20][21] but have not received much attention in one-dimensional (1D) systems such as quantum wires (QWR). Here, we present a theoretical study of the photocurrents in semiconductor QWRs.…”

“…Among several models to compute the electronic band structure, we choose to use the 14-band k • p model because it is able to describe the inversion asymmetry of GaAs and can be easily applied to semiconductor heterostructures. Using this approach, we recently obtained photocurrents including excitonic effects in bulk GaAs [11] and GaAs QWs [21]. It is shown that excitonic effects not only drastically change the existing shift current but also give ©2021 Vietnam Academy of Science and Technology rise to a ballistic current which is absent if the electron-hole attraction is not included.…”