Study of the initial stage of GaAs growth on FIB-modified silicon substrates

In this work, we studied the effect of the deposition thickness, growth rate, arsenic flux, and implantation dose on the morphology of the GaAs nanostructures grown on modified Si areas. It is shown that an increase in the growth rate at the initial stages of the growth process leads to the transition of the growth regime from layered-like to one-dimensional with the formation of nanowires. Studies of the effect of As4 pressure have shown that a change in the equivalent As4 flux in the range of 3.7 - 5.0 ML/s does not lead to any significant change in the structure of the GaAs layer in the modified areas. An increase in the implantation dose during processing with a focused ion beam led to disordering of the directions of the grown nanowires due to the degradation of the substrate crystal structure.

Perfect Selective Metamaterial Absorber With Thin-Film of GaAs Layer In The Visible Region For Solar Cell Applications

In this paper, we have presented a new design of a metamaterial perfect absorber (MPA) consisting of three layers of metal-dielectric-metal in which the top layer is considered of special kind square patches at different places in a unit cell. This MPA exhibits wideband, wide-angle, and polarization-independent absorption performance in the visible region. This structure originates the plasmonic resonance which is responsible for the perfect absorption in the optical region. Under a specific condition, this simulated absorber structure exhibits an extremely high broadband absorption between 591.54 nm to 704.40 nm wavelength range with near-unity absorption, and a single peak observed at 385.33 nm with absorption 94.16%. We extracted the impedance of the absorber and matched it with free space, and also demonstrated the effective permittivity and permeability. Moreover, the parametric study of the resonators, dielectric layer, and multi-band topology has also been investigated. The polarization-insensitive-based metamaterial may be utilized to improve the efficiency of different devices in the visible range. Furthermore, we have calculated the absorption of the proposed MPA under the solar radiation (AM1.5) for different structural parameters. The proposed absorber greatly enhances the conversion efficiency which is highly useful for solar cells. We also determined the short circuit current density of this absorber for different thicknesses of the GaAs layer. Al metal patches at meta-surface provide nearly similar performance in comparison with other costly metals. Therefore, the proposed structure with cheaper Al metal may be used for different devices as the perfect absorber.

Optical characteristics of type-II hexagonal shaped GaSb Quantum dots on GaAs synthesized using nanowire self-growth mechanism from Ga metal droplet

We report the growth mechanism and optical characteristics of type-II band-aligned GaSb quantum dots (QDs) grown on GaAs using droplet epitaxy-driven nanowire formation mechanism in with molecular beam epitaxy (MBE). Using transmission electron microscope (TEM) and scanning electron microscope (SEM) images, we confirmed that the QDs, which comprise zinc-blende crystal structures with hexagonal shape, were successfully grown through the formation of a nanowire from a Ga droplet with less strain between GaAs and GaSb. Photoluminescence (PL) peaks of GaSb, which are capped by the GaAs layer, are observed at 1.11 eV, 1.26 eV, and 1.47 eV, assigned to the QDs, a wetting-like layer (WLL), and bulk GaAs, respectively, at the measurement temperature of 14 K and excitation laser power of 30 mW. The integrated PL intensity of the QDs is significantly stronger than the WLL, which indicates well-grown GaSb QDs on GaAs and the generation of an interlayer exciton, as shown in the power and temperature-dependent PL, respectively. In addition, Time-resolved PL (TRPL) data show that the GaSb QD and GaAs layer form a self-aligned type-II band alignment, and temperature-dependent PL data exhibit a high equivalent internal quantum efficiency of 15+/-0.2%.

Влияние состава зародышевого слоя AlGaAs на формирование антифазных доменов в структурах (Al)GaAs, выращенных газофазной эпитаксией на подложках Ge/Si(100)

GaAs-based heterostructures grown by metalorganic vapor-phase epitaxy on virtual Ge/Si substrates using an AlxGa1-xAs seed layer with different aluminum content x in the solid solution are investigated. The effect of solid solution composition on the density and size of antiphase domains emerging on the sample surface and on the optical properties of the GaAs layer is shown. Si(100) substrates with a small unintentional miscut of 0.7° to [110] were used for growth.

Facet-Related Non-uniform Photoluminescence in Passivated GaAs Nanowires

The semiconductor nanowire architecture provides opportunities for non-planar electronics and optoelectronics arising from its unique geometry. This structure gives rise to a large surface area-to-volume ratio and therefore understanding the effect of nanowire surfaces on nanowire optoelectronic properties is necessary for engineering related devices. We present a systematic study of the non-uniform optical properties of Au-catalyzed GaAs/AlGaAs core–shell nanowires introduced by changes in the sidewall faceting. Significant variation in intra-wire photoluminescence (PL) intensity and PL lifetime (τPL) was observed along the nanowire axis, which was strongly correlated with the variation of sidewall facets from {112} to {110} from base to tip. Faster recombination occurred in the vicinity of {112}-oriented GaAs/AlGaAs interfaces. An alternative nanowire heterostructure, the radial quantum well tube consisting of a GaAs layer sandwiched between two AlGaAs barrier layers, is proposed and demonstrates superior uniformity of PL emission along the entire length of nanowires. The results emphasize the significance of nanowire facets and provide important insights for nanowire device design.

Large photocurrent density enhancement assisted by non-absorbing spherical dielectric nanoparticles in a GaAs layer

Herein, we report a theoretical investigation of large photocurrent density enhancement in a GaAs absorber layer due to non-absorbing spherical dielectric (SiO2) nanoparticles-based antireflection coating. The nanoparticles are embedded in a dielectric matrix (SiN) which improves the antireflection property of SiN ($$\lambda /4$$ λ / 4 coating) and let to pass more photons into the GaAs layer. The improvement is noticed omnidirectional and the highest is more than 100% at 85° angle of incidence with the nanoparticles’ surface filling density of 70%. Sunrise to sunset calculation of normalized photocurrent density over the course of a year have also shown improvements in the nanoparticles’ case.