Qiandong Zhuang

Intraband absorption in the 8–12 μm band from Si-doped vertically aligned InGaAs/GaAs quantum-dot superlattice

Normal-incident infrared absorption in the 8–12-μm-atmospheric spectral window in the InGaAs/GaAs quantum-dot superlattice is observed. Using cross-sectional transmission electron microscopy, we find that the InGaAs quantum dots are perfectly vertically aligned in the growth direction (100). Under the normal incident radiation, a distinct absorption peaked at 9.9 μm is observed. This work indicates the potential of this quantum-dot superlattice structure for use as normal-incident infrared imaging focal arrays application without fabricating grating structures.

Room temperature midinfrared electroluminescence from InSb/InAs quantum dot light emitting diodes

Self-assembled InSb submonolayer quantum dots (QDs) in an InAs matrix have been grown by molecular beam epitaxy using Sb2 and As2 fluxes. The structures exhibit bright midinfrared photoluminescence up to room temperature. Intense room temperature electroluminescence with a peak at wavelength near 3.8 μm was observed from p-i-n light emitting diode structures containing ten InSb submonolayer QD sheets inserted within the InAs active region.

Sb-induced phase control of InAsSb nanowires grown by molecular beam epitaxy

For the first time, we report a complete control of crystal structure in InAs(1-x)Sb(x) NWs by tuning the antimony (Sb) composition. This claim is substantiated by high-resolution transmission electron microscopy combined with photoluminescence spectroscopy. The pure InAs nanowires generally show a mixture of wurtzite (WZ) and zinc-blende (ZB) phases, where addition of a small amount of Sb (∼2-4%) led to quasi-pure WZ InAsSb NWs, while further increase of Sb (∼10%) resulted in quasi-pure ZB InAsSb NWs. This phase transition is further evidenced by photoluminescence (PL) studies, where a dominant emission associated with the coexistence of WZ and ZB phases is present in the pure InAs NWs but absent in the PL spectrum of InAs0.96Sb0.04 NWs that instead shows a band-to-band emission. We also demonstrate that the Sb addition significantly reduces the stacking fault density in the NWs. This study provides new insights on the role of Sb addition for effective control of nanowire crystal structure.

Room temperature photoluminescence at 4.5μm from InAsN

Nitrogen incorporation in InAsN epilayers grown by radio-frequency plasma-assisted molecular beam epitaxy was investigated as a function of growth conditions. Reduced growth rate, growth temperature, and arsenic flux significantly enhance the nitrogen incorporation. Optimal growth conditions allowed us to obtain high quality InAsN with nitrogen composition of up to 2.5%. The epilayers exhibit intense 4K photoluminescence (PL) with double-peak features, which were attributed to free carrier recombination and localized carrier recombination. Strong room temperature PL emission up to a wavelength of 4.5μm is obtained.

Molecular beam epitaxial growth of InAsN:Sb for midinfrared Optoelectronics

We report molecular beam epitaxial growth and characterization of dilute nitride InAsN:Sb. X-ray diffraction, energy dispersive x-ray spectrometry, and electron probe microanalysis revealed that nitrogen incorporation is significantly enhanced by introduction of Sb flux during growth, together with a dramatic improvement of the photoluminescence. These observations were attributed to the surfactant effect of Sb which suppresses the surface diffusion length of nitrogen and improves the homogeneity of the alloy. Sb incorporation is enhanced with the presence of nitrogen which was associated with the surface kinetic of growth. InAsN:Sb∕InAs p-i-n light emitting diodes operating near 4.0μm were also realized.

Linear magnetoresistance due to multiple-electron scattering by low-mobility islands in an inhomogeneous conductor

Linear transverse magnetoresistance is commonly observed in many material systems including semimetals, narrow band-gap semiconductors, multi-layer graphene and topological insulators. It can originate in an inhomogeneous conductor from distortions in the current paths induced by macroscopic spatial fluctuations in the carrier mobility and it has been explained using a phenomenological semiclassical random resistor network model. However, the link between the linear magnetoresistance and the microscopic nature of the electron dynamics remains unknown. Here we demonstrate how the linear magnetoresistance arises from the stochastic behaviour of the electronic cycloidal trajectories around low-mobility islands in high-mobility inhomogeneous conductors and that this process is only weakly affected by the applied electric field strength. Also, we establish a quantitative link between the island morphology and the strength of linear magnetoresistance of relevance for future applications.

Surfactant effect of antimony addition to the morphology of self-catalyzed InAs1−xSbx nanowires

The effect of Sb addition on the morphology of self-catalyzed InAsSb nanowires (NWs) has been systematically investigated. InAs NWs were grown by molecular beam epitaxy with and without antimony (Sb) flux. It is demonstrated that trace amounts of Sb flux are capable of tuning the geometry of NWs, i.e., enhancing lateral growth and suppressing axial growth. We attribute this behavior to the surfactant effect of Sb which results in modifications to the kinetic and thermodynamic processes. A thermodynamic mechanism that accounts for Sb segregation in InAsSb NWs is also elucidated. This study opens a new route towards precisely controlled NW geometries by means of Sb addition.

Midinfrared Photoreflectance Study of InAs-rich InAsSb and GaInAsPSb Indicating Negligible Bowing for the Spin Orbit Splitting Energy

The authors report on midinfrared photoreflectance measurements of the band gap (E0) and spin-orbit splitting energies (Δ0) in InAs-rich InAsSb and GaInAsPSb samples for varying antimony contents ⩽22.5%. The E0 behavior as a function of Sb content is consistent with the literature value bowing parameter of ∼670meV. However, Δ0 does not exhibit the positive bowing of +1170meV quoted in the literature: rather, a best fit to their data tentatively suggests a negative bowing of −225meV. This result is likely to have strong impact due to the importance of the Δ0 parameter in governing InAsSb-based device performance.

Influence of indium composition on the surface morphology of self-organized InxGa1−xAs quantum dots on GaAs substrates

InxGa1-xAs self-organized quantum dots with x=1.0, 0.5, and 0.35 have been grown by molecular beam epitaxy. The areal density, distribution, and shapes have been found to be dependent on x. The dot shape changes from a round shape for x=1.0 to an elliptical shape for x less than or equal to 0.5. The major axis and minor axis of the elliptical InxGa1-xAs dots are along the [(1) over bar 10] and [110] directions, respectively. The ordering phenomenon is also discussed. It is suggested that the dot-dot interaction may play important roles in the self-organization process

GaSb quantum dot morphology for different growth temperatures and the dissolution effect of the GaAs capping layer

We compare the characteristics of GaSb quantum dots (QDs) grown by molecular beam epitaxy on GaAs at temperatures from 400°C to 490°C. The dot morphology, in terms of size, shape and density, as determined by atomic force microscopy on uncapped QDs, was found to be highly sensitive to the growth temperature. Photoluminescence spectra of capped QDs are also strongly dependent on growth temperature, but for samples with the highest dot density, where the QD luminescence would be expected to be the most intense, it is absent. We attribute this to dissolution of the dots by the capping layer. This explanation is confirmed by atomic force microscopy of a sample that is thinly capped at 490°C. Deposition of the capping layer at low temperature resolves this problem, resulting in strong QD photoluminescence from a sample with a high dot-density.