Yp Song

Magnetically confined plasma reactive ion etching of GaAs/AlGaAs/AlAs quantum nanostructures

An electron cyclotron resonance reactive ion etching machine has been successfully run under low magnetic field conditions. We call this the magnetically confined plasma condition. Under this condition, a new process using SiCl4 with a small amount of O2 has been developed for etching nanometer scale structures on GaAs, AlGaAs, and AlAs multilayer materials. The effects of the percentage of O2, the rf power, the microwave power, and the flow rate are described. 100 nm quantum dots have been etched on multiple quantum well materials to a depth of about 1 μm. Vertical and smooth sidewalls were obtained on these nanostructures. Poly‐methylmethacrylate (PMMA) electron beam resist can be used directly as a dry etch mask, and the selectivity between GaAs and PMMA can be as high as 28:1. Raman spectroscopic studies showed that the process induced no detectable damage to the surface for an etch depth of 130 nm and only very little damage for deeper etching.

Quantitative analysis of elastic strains in GaAs/AlAs quantum dots

Abstract We have studied a GaAs/AlAs periodic quantum dot array using reciprocal space mapping around the (0 0 4) and ( 1 1 3 ) reciprocal lattice points. Both the coherently and the diffusely scattered X-ray intensities were analyzed by performing two-dimensional model calculations. From the distribution of the diffracted intensities we deduced the average strain status in the dots. From the numerical simulations it is evident that random elastic strain fields are present, which extend through almost the entire volume of the quantum dot. The simulations of the X-ray measurements revealed that the crystalline part of the dots is considerably smaller as scanning electron micrographs would indicate.

X‐ray reciprocal space mapping of GaAs/AlAs quantum wires and quantum dots

Periodic arrays of 150 and 175 nm‐wide GaAs–AlAs quantum wires and quantum dots were investigated, fabricated by electron beam lithography, and SiCl4/O2 reactive ion etching, by means of reciprocal space mapping using triple axis x‐ray diffractometry. From the x‐ray data the lateral periodicity of wires and dots, and the etch depth are extracted. The reciprocal space maps reveal that after the fabrication process the lattice constant along the growth direction slightly increases for the wires and even more so for the dots.

Magnetically confined plasma reactive ion etching and photoluminescence of GaAs quantum wires

Magnetically confined plasma reactive ion etching has been used, with SiCl4 with a small amount of O2 as process gases, to etch quantum wires of GaAs multiple quantum wells with AlAs barriers. The impact of adding oxygen is discussed. Vertical and smooth sidewalls were obtained for these structures with a high aspect ratio. Photoluminescence of etched quantum wires shows 1D subbands.

Elastic strains in GaAs/AIAs quantum dots studied by high-resolution x-ray diffraction

Abstract We have studied a GaAs AlAs quantum dot array using reciprocal space mapping around the (004) and (II3) reciprocal lattice points. Both the coherently and the diffusely scattered X-ray intensities were analysed by performing two-dimensional model calculations. From the distribution of the diffracted intensities we deduced the average strain status in the dots. From the numerical simulations it is evident that random elastic strain fields are present, which extend through almost the whole volume of the quantum dot. The simulations of the X-ray measurements revealed that the crystalline part of the dots is considerably smaller as scanning electron micrographs would indicate, namely 50 nm instead of 65 nm, respectively.

Inelastic light scattering from electronic excitations in deep-etched quantum dots and wires

Abstract Resonant Raman spectroscopy of modulation-doped GaAs/AlGaAs multiple quantum well dots and wires is reported. Deep etching with a SiCl 4 reactive ion etching process achieved an excellent aspect ratio (>10:1) and low surface damage for dots and wires of sizes in the range 60–250 nm. A rich spectrum of single particle excitations was observed at Raman shifts in the range 1–35 meV for both dots and wires. Sharp resonances were found for the Raman intensities. The electronic scattering in wires exhibits distinct polarization properties in agreement with theoretical predictions and the spin density excitation energies are in reasonable agreement with Hartree approximation calculations. The dispersion of the intrasubband plasmon collective mode in 60 nm wires has been determined. The excitations in dots show a systematic shift to higher energy with decreasing dot diameter consistent with increased confinement. Magneto-Raman scattering from dot samples was also investigated at magnetic fields up to 12 T and the excitation spectra show level splitting, level crossing and mode softening with increasing magnetic field.

Crystalline and Quasi-crystalline Patterns in X-Ray Diffraction from Periodic Arrays of Quantum Dots

The structural properties of a square periodic array of quantum dots of a GaAs/AlAs superlattice were studied by x-ray diffractometry. If the azimuthal direction of the primary beam can be expressed by integer Miller indices, the profile is perfectly periodic. However, if its azimuthal orientation is determined by tg() ≈ 0.618 (the golden mean value), the diffraction maxima exhibit Fibonacci sequences in reciprocal space, i.e. a quasi-periodic diffraction curve.

Determination of the Strain Status of GaAs/AlAs Quantum Wires and Quantum Dots

We have investigated periodic arrays of 150 and 175 nm wide GaAs-AlAs quantum wires and quantum dots, fabricated by electron beam lithography and SiCI 4 /O 2 reactive ion etching, by means of reciprocal space mapping using triple axis x-ray diffractometry (TAD). The reciprocal space maps reveal that after the fabrication process the lattice constant along the growth direction slightly increases for the wires and even more so for the dots.