We consider terahertz absorption and gain in a single miniband of semiconductor superlattice subject to a bichromatic electric field in the most general case of commensurate frequencies of the probe and pump fields. Using an exact solution of Boltzmann transport equation, we show that in the small-signal limit the formulas for absorption always contain two distinct terms related to the parametric and incoherent interactions of miniband electrons with the alternating pump field. It provides a theoretical background for a control of THz gain without switching to the negative differential conductivity state. For pedagogical reasons we present derivations of formulas in detail.
Electron transmission through semiconductor superlattices is studied with transfer matrix method and resonance theory. The formation of electron band-pass transmission is ascribed to the coupling of different modes in those semiconductor superlattices with the symmetric unit cell. Upon Fabry-Pérot resonance condition, Bloch modes and two other resonant modes are identified to be related to the nature of the superlattice and its unit cell, respectively. The bands related to the unit cell and the superlattice overlap spontaneously in the tunneling region due to the shared wells, and the coupling…
We report first evidence for a 1.0 terahertz (THz) self-starting mirrorless acoustic phonon parametric oscillator (MAPPO) produced from acousto-optic phase-conjugate degenerate four-wave (D4WM) mixing in a THz laser-pumped silicon doping superlattice (DSL). The DSL was grown by molecular beam epitaxy on a (100) boron-doped silicon substrate. A superconducting NbTiN subwavelength grating was used to couple the THz laser radiation into the DSL. Superconducting granular aluminum bolometric detection, coupled with Si:B piezophonon spectroscopy, revealed excitation of THz coherent compressional and…
The exciton absorption coefficient is determined analytically for a semiconductor superlattice in crossed electric and magnetic fields, for the magnetic field being parallel and the electric field being perpendicular to the superlattice axis. Our investigation applies to the case where the magnetic length, while being much smaller than the exiton Bohr radius, considerably exceeds the superlattice period. The optical absorption in superlattices displays a spectral fine structure related to the sequences of exciton states bound whose energies are adjacent to the Landau energies of the charge car…
We study the response of low-dimensional semiconductor superlattices to strong terahertz fields on condition of a strong suppression of inelastic scattering processes of electrons caused by the polar-optical phonons. For our study we employ a balance equations approach which allows investigating the response of the superlattices to strong terahertz fields taking account of both the inelastic and the strongly pronounced elastic scattering of electrons. Our approach provides a way to analyze the influence of the Bloch dynamics of electrons in a superlattice miniband side by side with the effects…
In semiconductor superlattices, when Bragg oscillating electrons interact with an input electromagnetic field, frequency multiplication is possible. An ideal superlattice has a purely antisymmetric voltage current response and can thus produce only odd harmonics. However, real world superlattices can also have even harmonic response and that increases the range of possible output frequencies. These effects have been recently explained with a predictive model that combines an Ansatz solution for the Boltzmann Equation with a Nonequilibrium Green's Functions approach. This predictive tool, coupl…
In twisted homobilayer transition metal dichalcogenides, intra- and inter-layer valley excitons hybridize with the layer configurations spatially varying in the moiré. The ground state valley excitons are trapped at two high-symmetry points with opposite electric dipoles in a moiré supercell, forming a honeycomb superlattice of nearest-neighbor dipolar attraction. We find that the spatial texture of layer configuration results in a luminescence anomaly of the moiré trapped excitons, where a tiny displacement by interactions dramatically increases the brightness and changes polarization from ci…
This paper applies analytical approximations for the luminescence of short period semiconductor superlattices and analyses the low density regime, demonstrating that the theory clearly connects with low density absorption with ratios of oscillator strengths of bound and continuum states as expected from the Elliott formula. A numerical study illustrates in detail the bleaching of higher order bound state. The analytical expressions have potential for systematic studies of controlled excitonic pathways characterized by THz responses.
Electron dynamics in intentionally disordered semiconductor superlattices
我们研究了无序量子阱半导体超晶格的动力学行为，其中无序是有意的和短程关联的。我们发现，而一个粒子的传输时间的增长与井的数量在一个通常的无序超晶格的入射粒子能量的任何值呈指数关系，对于特定的入射能量值，这个时间线性增加时，包括相关的障碍。正如预期的那样，这些能量值与Dom \em et al.} [Phys. Rev. B { \bf 51}，14，359（1994）];在我们的动力学结果中看到这样的状态表现出弹道状态，非常接近完美超晶格的WKB近似。对入射高斯波包的输出信号进行傅里叶变换，揭示了原始信号的戏剧性滤波，这使我们相信，基于此属性的设备可以被设计并用于纳米技术应用。考虑到使用直流电场来抑制输出频带的可能性，我们也讨论了这一点。在结论中，我们总结了我们的结果，并提出了未来的发展前景，从这项工作。
Wannier-Mott excitons in a semiconductor layered superlattice (SL) of period much smaller than the 2D exciton Bohr radius in the presence of a longitudinal external dc electric field directed parallel to the SL axis are investigated analytically. The exciton states and the optical absorption coefficient are derived in the tight-binding and adiabatic approximations. Strong and weak electric fields providing spatially localized and extended electron and hole states, respectively, are studied. The dependencies of the exciton states and the exciton absorption spectrum on the SL parameters and the …
Interlayer coupling in ferromagnetic semiconductor superlattices
本文发展了稀磁半导体载流子感生铁磁性的平均场论。我们的方法代表了一个标准的RKKY模型的改进，允许系统的空间不均匀性，自由载流子自旋极化，有限的温度，自由载流子交换和相关性要考虑自洽。作为一个例子，我们计算了Mn $_x$ Ga $_{1-x}$ As/GaAs超晶格的电子结构，证明了半导体磁电阻系统具有设计特性的可能性。
