Novel Dilute Bismide, Epitaxy, Physical Properties and Device Application

Plasmon Resonance in a System of Bi Nanoparticles Embedded into (Al,Ga)As Matrix

We reveal the feasibility of the localized surface plasmon resonance in a system of Bi nanoparticles embedded into an AlxGa1-xAs semiconductor matrix. With an ab initio determined dielectric function for bismuth and well-known dielectric properties of AlxGa1-xAs solid solution, we performed calculations of the optical extinction spectra for such metamaterial using Mie's theory. The calculations demonstrate a strong band of the optical extinction using the localized surface plasmons near a photon energy of 2.5 eV. For the semiconducting matrices with a high aluminum content x>0.7, the extinction by plasmonic nanoparticles plays the dominant role in the optical properties of the medium near the resonance photon energy.

Lattice dynamics and carrier recombination in GaAs/GaAsBi nanowires

GaAsBi nanowires represent a novel and promising material platform for future nano-photonics. However, the growth of high-quality GaAsBi nanowires and GaAsBi alloy is still a challenge due to a large miscibility gap between GaAs and GaBi. In this work we investigate effects of Bi incorporation on lattice dynamics and carrier recombination processes in GaAs/GaAsBi core/shell nanowires grown by molecular-beam epitaxy. By employing photoluminescence (PL), PL excitation, and Raman scattering spectroscopies complemented by scanning electron microscopy, we show that increasing Bi-beam equivalent pressure (BEP) during the growth does not necessarily result in a higher alloy composition but largely affects the carrier localization in GaAsBi. Specifically, it is found that under high BEP, bismuth tends either to be expelled from a nanowire shell towards its surface or to form larger clusters within the GaAsBi shell. Due to these two processes the bandgap of the Bi-containing shell remains practically independent of the Bi BEP, while the emission spectra of the NWs experience a significant red shift under increased Bi supply as a result of the localization effect.

Temperature-independent lasing wavelength of highly stacked InAs quantum dot laser fabricated on InP(311)B substrate with Bi irradiation

In this study, the effects of bismuth (Bi) irradiation on InAs quantum dot (QD) lasers operating in the telecommunication wavelength band were investigated. Highly stacked InAs QDs were grown on an InP(311)B substrate under Bi irradiation, and a broad-area laser was fabricated. In the lasing operation, the threshold currents were almost the same, regardless of Bi irradiation at room temperature. These QD lasers were operated at temperatures between 20 and 75°C, indicating the possibility of high-temperature operation. In addition, the temperature dependence of the oscillation wavelength changed from 0.531 nm/K to 0.168 nm/K using Bi in the temperature range 20-75°C.

Phase Control Growth of InAs Nanowires by Using Bi Surfactant

To realize practical applications of nanowire-based devices, it is critical, yet challenging, to control crystal structure growth of III-V semiconductor nanowires. Here, we demonstrate that controlled wurtzite and zincblende phases of InAs nanowires can be fabricated using bismuth (Bi) as a surfactant. For this purpose, catalyst free selective area epitaxial growth of InAs nanowires was performed using molecular beam epitaxy (MBE). During the growth, Bi was used which may act as a wetting agent influencing the surface energy at growth plane ends, promoting wurtzite crystal phase growth. For a demonstration, wurtzite and zincblende InAs nanowires were obtained with and without using Bi-flux. Photoluminescence spectroscopy (PL) analysis of the nanowires indicates a strong correlation between wurtzite phase and the Bi-flux. It is observed that the bandgap energy of wurtzite and zincblende nanowires are ∼0.50 eV and ∼0.42 eV, respectively, and agree well with theoretical estimated bandgap of corresponding InAs crystal phases. A blue shift in PL emission peak energy was found with decreasing nanowire diameter. The controlled wurtzite and zincblende crystal phase and its associated heterostructure growth of InAs nanowires on Si may open up new opportunities in bandgap engineering and related device applications integrated on Si. Furthermore, this work also illustrates that Bi as a surfactant could play a dynamic role in the growth mechanism of III-V compound semiconductors.

Analysis of Current Transport Mechanism in AP-MOVPE Grown GaAsN p-i-n Solar Cell

Basic knowledge about the factors and mechanisms affecting the performance of solar cells and their identification is essential when thinking of future improvements to the device. Within this paper, we investigated the current transport mechanism in GaAsN p-i-n solar cells grown with atmospheric pressure metal organic vapour phase epitaxy (AP-MOVPE). We examined the electro-optical and structural properties of a GaAsN solar cell epitaxial structure and correlated the results with temperature-dependent current-voltage measurements and deep level transient spectroscopy findings. The analysis of J-V-T measurements carried out in a wide temperature range allows for the determination of the dominant current transport mechanism in a GaAsN-based solar cell device and assign it a nitrogen interstitial defect, the presence of which was confirmed by DLTFS investigation.

Structural Quality and Magnetotransport Properties of Epitaxial Layers of the (Ga,Mn)(Bi,As) Dilute Magnetic Semiconductor

Structural analysis of epitaxial layers of the (Ga,Mn)(Bi,As) quaternary dilute magnetic semiconductor (DMS), together with investigations of their magnetotransport properties, has been thoroughly performed. The obtained results are compared with those for the reference (Ga,Mn)As layers, grown under similar conditions, with the aim to reveal an impact of Bi incorporation on the properties of this DMS material. Incorporation of Bi into GaAs strongly enhances the spin-orbit coupling strength in this semiconductor, and the same has been expected for the (Ga,Mn)(Bi,As) alloy. In turn, importantly for specific spintronic applications, strong spin-orbit coupling in ferromagnetic systems opens a possibility of directly controlling the direction of magnetization by the electric current. Our investigations, performed with high-resolution X-ray diffractometry and transmission electron microscopy, demonstrate that the (Ga,Mn)(Bi,As) layers of high structural quality and smooth interfaces can be grown by means of the low-temperature molecular-beam epitaxy method, despite a large difference between the sizes of Bi and As atoms. Depending on the applied buffer layer, the DMS layers can be grown under either compressive or tensile misfit strain, which influences their magnetic properties. It is shown that even small 1% Bi content in the layers strongly affects their magnetoelectric properties, such as the coercive field and anisotropic magnetoresistance.

Effects of Bi incorporation on recombination processes in wurtzite GaBiAs nanowires

The effects of Bi incorporation on the recombination process in wurtzite (WZ) GaBiAs nanowires are studied by employing micro-photoluminescence (μ-PL) and time-resolved PL spectroscopies. It is shown that at low temperatures (T < 75 K) Bi-induced localization effects cause trapping of excitons within band-tail states, which prolongs their lifetime and suppresses surface nonradiative recombination (SNR). With increasing temperature, the trapped excitons become delocalized and their lifetime rapidly shortens due to facilitated SNR. Furthermore, Bi incorporation in the GaBiAs NW is found to have a minor influence on the surface states responsible for SNR.

Controlling Bi-Provoked Nanostructure Formation in GaAs/GaAsBi Core-Shell Nanowires

We control the formation of Bi-induced nanostructures on the growth of GaAs/GaAsBi core-shell nanowires (NWs). Bi serves as not only a constituent but also a surfactant and nanowire growth catalyst. Thus, we paved a way to achieve unexplored III-V nanostructures employing the characteristic supersaturation of catalyst droplets, structural modifications induced by strain, and incorporation into the host GaAs matrix correlated with crystalline defects and orientations. When Ga is deficient during growth, Bi accumulates on the vertex of core GaAs NWs and serves as a nanowire growth catalyst for the branched structures to azimuthal <112>. We find a strong correlation between Bi accumulation and stacking faults. Furthermore, Bi is preferentially incorporated on the GaAs (112)B surface, leading to spatially selective Bi incorporation into a confined area that has a Bi concentration of over 7%. The obtained GaAs/GaAsBi/GaAs heterostructure with an interface defined by the crystalline twin defects in a zinc-blende structure can be potentially applied to a quantum confined structure. Our finding provides a rational design concept for the creation of GaAsBi based nanostructures and the control of Bi incorporation beyond the fundamental limit.

Variation of the photoluminescence spectrum of InAs/GaAs heterostructures grown by ion-beam deposition

This work reports on an experimental investigation of the influence of vertical stacking of quantum dots, the thickness of GaAs potential barriers, and their isovalent doping with bismuth on the photoluminescence properties of InAs/GaAs heterostructures. The experimental samples were grown by ion-beam deposition. We showed that using three vertically stacked layers of InAs quantum dots separated by thin GaAs barrier layers was accompanied by a red-shift of the photoluminescence peak of InAs/GaAs heterostructures. An increase in the thickness of the GaAs barrier layers was accompanied by a blue shift of the photoluminescence peak. The effect of isovalent Bi doping of the GaAs barrier layers on the structural and optical properties of the InAs/GaAs heterostructures was investigated. It was found that the Bi content up to 4.96 atom % in GaAs decreases the density of InAs quantum dots from 1.53 × 1010 to 0.93 × 1010 cm-2. In addition, the average lateral size of the InAs quantum dots increased from 14 to 20 nm, due to an increase in the surface diffusion of In. It is shown that isovalent doping of GaAs potential barriers by bismuth was accompanied by a red-shift of the photoluminescence peak of InAs quantum dots of 121 meV.