AlGaAs inverted strip buried heterostructure lasers

Inverted strip buried heterostructure lasers have been fabricated. These lasers have threshold currents and quantum efficiencies that are comparable to those of conventional buried heterostructure lasers. The optical mode is confined by a weakly guiding strip loaded waveguide which makes possible operation in the fundamental transverse mode for larger stripe widths than is possible for conventional buried heterostructure lasers. Scattering of the laser light by irregularities in the sidewalls of the waveguide, which can be a serious problem in conventional buried heterostructure lasers, is also greatly reduced in these lasers

Tin monochalcogenide heterostructures as mechanically rigid infrared bandgap semiconductors

Based on first-principles density functional calculations, we show that SnS and SnSe layers can form mechanically rigid heterostructures with the constituent puckered or buckled monolayers. Due to the strong interlayer coupling, the electronic wavefunctions of the conduction and valence band edges are delocalized across the heterostructure. The resultant bandgap of the heterostructures reside in the infrared region. With strain engineering, the heterostructure bandgap undergoes transition from indirect to direct in the puckered phase. Our results show that there is a direct correlation between the electronic wavefunction and the mechanical rigidity of the layered heterostructure

Strong magnetization and Chern insulators in compressed graphene/CrI3_{3} van der Waals heterostructures

Graphene-based heterostructures are a promising material system for designing the topologically nontrivial Chern insulating devices. Recently, a two-dimensional (2D) monolayer ferromagnetic insulator CrI$_{3}$ was successfully synthesized in experiments [Huang et al., Nature 546, 270 (2017)]. Here, these two interesting materials are proposed to build a heterostructure (Gr/CrI$_{3}$). Our first-principles calculations show that the system forms a van der Waals (vdW) heterostructure, relatively facilely fabricated in experiments. A Chern insulating state is acquired in the Gr/CrI$_{3}$ heterostructure if the vdW gap is compressed to certain extents by applying an external pressure. Amazingly, very strong magnetization (about 150 meV) is found in graphene, induced by the substrate CrI$_{3}$, despite the vdW interactions between them. A low-energy effective model is employed to understand the mechanism. The work functions, contact types, and band alignments of the Gr/CrI$_{3}$ heterostructure system are also studied. Our work demonstrates that the Gr/CrI$_{3}$ heterostructure is a promising system to observe the quantum anomalous Hall effect at high temperatures (up to 45 K) in experiments.Comment: 9 pages, 5 figure

Using ultrashort optical pulses to couple ferroelectric and ferromagnetic order in an oxide heterostructure

A new approach to all-optical detection and control of the coupling between electric and magnetic order on ultrafast timescales is achieved using time-resolved second harmonic generation (SHG) to study a ferroelectric (FE)/ferromagnet (FM) oxide heterostructure. We use femtosecond optical pulses to modify the spin alignment in a Ba$_{0.1}$Sr$_{0.9}$TiO$_{3}$(BSTO)/La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ (LCMO) heterostructure and selectively probe the ferroelectric response using SHG. In this heterostructure, the pump pulses photoexcite non-equilibrium quasiparticles in LCMO, which rapidly interact with phonons before undergoing spin-lattice relaxation on a timescale of tens of picoseconds. This reduces the spin-spin interactions in LCMO, applying stress on BSTO through magnetostriction. This then modifies the FE polarization through the piezoelectric effect, on a timescale much faster than laser-induced heat diffusion from LCMO to BSTO. We have thus demonstrated an ultrafast indirect magnetoelectric effect in a FE/FM heterostructure mediated through elastic coupling, with a timescale primarily governed by spin-lattice relaxation in the FM layer

Optical Properties of GaS-Ca(OH)2_2 bilayer heterostructure

Finding novel atomically-thin heterostructures and understanding their characteristic properties are critical for developing better nanoscale optoelectronic devices. In this study, we investigate the electronic and optical properties of GaS-Ca(OH)$_2$ heterostructure using first-principle calculations. The band gap of the GaS-Ca(OH)$_2$ heterostructure is significantly reduced when compared with those of the isolated constituent layers. Our calculations show that the GaS-Ca(OH)$_2$ heterostructure is a type-II heterojunction which can be used to separate photoinduced charge carriers where electrons are localized in GaS and holes in the Ca(OH)$_2$ layer. This leads to spatially indirect excitons which are important for solar energy and optoelectronic applications due to their long lifetime. By solving the Bethe-Salpeter equation on top of single shot GW calculation (G$_0$W$_0$) the dielectric function and optical oscillator strength of the constituent monolayers and the heterostructure are obtained. The oscillator strength of the optical transition for GaS monolayer is an order of magnitude larger than Ca(OH)$_2$ monolayer. We also found that the calculated optical spectra of different stacking types of the heterostructure show dissimilarities, although their electronic structures are rather similar. This prediction can be used to determine the stacking type of ultra-thin heterostructures

Density-functional theory study of half-metallic heterostructures: interstitial Mn in Si

Using density-functional theory within the generalized gradient approximation, we show that Si-based heterostructures with 1/4 layer $\delta$-doping of {\em interstitial} Mn (Mn$_{\mathrm int}$) are half-metallic. For Mn$_{\mathrm int}$ concentrations of 1/2 or 1 layer, the states induced in the band gap of $\delta$-doped heterostructures still display high spin polarization, about 85% and 60%, respectively. The proposed heterostructures are more stable than previously assumed $\delta$-layers of {\em substitutional} Mn. Contrary to wide-spread belief, the present study demonstrates that {\em interstitial} Mn can be utilized to tune the magnetic properties of Si, and thus provides a new clue for Si-based spintronics materials.Comment: 5 pages, 4 figures, PRL accepte