GaAs Nanodisks Research Articles

Photoluminescence emission from GaAs nanodisks in GaAs/AlGaAs nanopillar arrays fabricated by neutral beam etching

GaAs quantum nanodisks (QNDs) in nanopillar (NP) arrays are considered to be an attractive candidate for photonic device applications. We report a damageless fabrication technique that can be used to produce large-area lattice-matched GaAs/AlGaAs heterostructure NP arrays through the use of a bio-template and neutral beam etching. We have successfully realized GaAs QNDs in NPs owing to nanoscale iron oxide masks included in poly(ethylene glycol)-decorated ferritin protein shells. We observed for first time the photoluminescence emission from as-etched GaAs QNDs and confirmed quantum confinement by quantum mechanical calculation. Our methodology is vital for high-efficiency pillar-based optoelectronic devices such as NP laser diodes.

Publisher's Note: Tuning of the electrongfactor in defect-free GaAs nanodisks [Phys. Rev. B92, 245423 (2015)

Publisher's Note: Tuning of the electron<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>g</mml:mi></mml:math>factor in defect-free GaAs nanodisks [Phys. Rev. B<b>92</b>, 245423 (2015)

Tuning of the electrongfactor in defect-free GaAs nanodisks

We theoretically study the impact of changes in surroundings on the electron ground-state effective $g$ factor in defect-free GaAs/AlGaAs nanodisks. To perform the study, we formulate and deploy a computational efficient full three-dimensional model to describe the effective $g$-factor tensor in semiconductor nano-objects of complex geometry and material content. This model is based on an effective $2\ifmmode\times\else\texttimes\fi{}2$ conduction-band Hamiltonian which includes the Rashba and Dresselhaus spin-orbit couplings. The description is suited to clarify the important question of the controllability of the electron effective $g$ factor in semiconductor nano-objects. The results of this theoretical study suggest that in the defect-free GaAs/AlGaAs nanodisks, the effective $g$ factor can be tuned within a wide range by proper design of the nanodisk environment. The $zz$ components of the electron effective $g$-factor tensor obtained in our simulation are in good agreement with some recent experimental observations.

Light-emitting devices based on top-down fabricated GaAs quantum nanodisks.

Quantum dots photonic devices based on the III–V compound semiconductor technology offer low power consumption, temperature stability, and high-speed modulation. We fabricated GaAs nanodisks (NDs) of sub-20-nm diameters by a top-down process using a biotemplate and neutral beam etching (NBE). The GaAs NDs were embedded in an AlGaAs barrier regrown by metalorganic vapor phase epitaxy (MOVPE). The temperature dependence of photoluminescence emission energies and the transient behavior were strongly affected by the quantum confinement effects of the embedded NDs. Therefore, the quantum levels of the NDs may be tuned by controlling their dimensions. We combined NBE and MOVPE in a high-throughput process compatible with industrial production systems to produce GaAs NDs with tunable optical characteristics. ND light emitting diode exhibited a narrow spectral width of 38 nm of high-intensity emission as a result of small deviation of ND sizes and superior crystallographic quality of the etched GaAs/AlGaAs layer.

Electron g-factor and spin decoherence in GaAs quantum nanodisks fabricated by fully top-down lithography

GaAs nanodisks (NDs), with a thickness of 8nm and a diameter of 15nm, were directly fabricated from GaAs quantum wells (QW) by damage-free neutral-beam etching using bio-nanotemplates. We observed the electron g-factor and spin dephasing in NDs with different barrier heights in the lateral direction by means of time-resolved Kerr rotation. The magnitude of the g-factor depends on the degree of lateral confinement originating from enhanced penetration of the electron wavefunction from an ND into the surrounding AlGaAs barriers. The spin-dephasing time is also observed to be altered by ND formation.

Impact of artificial lateral quantum confinement on exciton-spin relaxation in a two-dimensional GaAs electronic system

We demonstrate the effect of artificial lateral quantum confinement on exciton-spin relaxation in a GaAs electronic system. GaAs nanodisks (NDs) were fabricated from a quantum well (QW) by top-down nanotechnology using neutral-beam etching aided by protein-engineered bio-nano-templates. The exciton-spin relaxation time was 1.4 ns due to ND formation, significantly extended compared to 0.44 ns for the original QW, which is attributed to weakening of the hole-state mixing in addition to freezing of the carrier momentum. The temperature dependence of the spin-relaxation time depends on the ND thickness, reflecting the degree of quantum confinement.

Selectively grown GaAs nanodisks on Si(100) by molecular beam epitaxy

The authors report the molecular beam epitaxial growth and the structural and optical characterizations of self-assembled/catalyst-free GaAs nanodisks on SiO2 masked Si(100) patterned substrates. Pure zincblende GaAs nanodisks with precise positioning and low defect density are demonstrated by selective area epitaxy. The influence of the growth temperature and deposition duration is investigated. Excellent morphological and structural properties are characterized by scanning electron microscopy and cross-sectional transmission electron microscopy. Defects in the epilayers are reduced by strain relaxation through facets formation and by a lateral overgrowth scheme atop the SiO2 mask which is corroborated by microRaman spectroscopy. In particular, the authors show how the material quality contributes to excellent optical properties observed by microphotoluminescence spectroscopy from 77 K to room temperature.

Quantum size effects in GaAs nanodisks fabricated using a combination of the bio-template technique and neutral beam etching

We successfully fabricated defect-free, distributed and sub-20-nm GaAs quantum dots (named GaAs nanodisks (NDs)) by using a novel top-down technique that combines a new bio-template (PEGylated ferritin) and defect-free neutral beam etching (NBE). Greater flexibility was achieved when engineering the quantum levels of ND structures resulted in greater flexibility than that for a conventional quantum dot structure because structures enabled independent control of thickness and diameter parameters. The ND height was controlled by adjusting the deposition thickness, while the ND diameter was controlled by adjusting the hydrogen-radical treatment conditions prior to NBE. Photoluminescence emission due to carrier recombination between the ground states of GaAs NDs was observed, which showed that the emission energy shift depended on the ND diameters. Quantum level engineering due to both diameter and thickness was verified from the good agreement between the PL emission energy and the calculated quantum confinement energy.

Photoluminescence from GaAs nanodisks fabricated by using combination of neutral beam etching and atomic hydrogen-assisted molecular beam epitaxy regrowth

We have fabricated GaAs nanodisk (ND) structures by using a combination of neutral beam etching process and atomic hydrogen-assisted molecular beam epitaxy regrowth. We have observed clear photoluminescence (PL) emissions from GaAs NDs. The peak energy showed a blueshift due to the quantum confinement in three spatial dimensions, and it agreed with the theoretically estimated transition energy. The PL results also showed that the cap-layer disks act as radiative recombination centers. We have confirmed that the PL emission originates from the GaAs NDs, and our approach is effective for the fabrication of high quality ND structures.