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Local droplet etching (LDE) drills self-assembled nanoholes into AlGaAs surfaces and represents a powerful technique for the fabrication of versatile quantum structures like quantum dots, rings, and molecules. Usually, LDE is performed at temperatures T = 600 − 680 ° C if Al is used as the etching material. Now, atomic force microscopy establishes that Al-LDE drills nanoholes also at very low temperatures down to T = 360 ° C which is 300 ° C below the melting point of bulk Al. Several possible etching mechanisms like a melting-point depression, solid-state etching, and alloying are discussed. Selective wet-chemical etching experiments using HF indicate significant alloying with Ga from the substrate, and thus the formation of Al-Ga droplets for etching. The upper limit of x ≤ 50 % for the Al content inside the Al-Ga droplets is indicated by the selectivity of the HF acid. This value is in agreement with an estimation of x = 0.42, which is based on the measured droplet and hole volumes. A comparison with the Al-Ga phase diagram indicates that a completely liquid phase of the droplets is essential for etching.

MgO tunneling barriers are extensively studied as a spin filtering and diffusion barrier for deposition of ferromagnetic layers on GaAs (001) surfaces. The relatively large lattice mismatch of the MgO and GaAs substrate and probable formation of interface states at the metal layer side require a careful barrier design. We present a study of deposition, microstructure, and strain relaxation in MgO barriers deposited on GaAs. The dependence of morphology of MgO layers on their thickness was characterized using a combination of X-Ray Reflectivity and High Resolution Transmission Electron Microscopy. The stress at the MgO/GaAs interface was observed to be released through the formation of misfit dislocations and partially by the formation of mis-oriented domains. The deposited MgO and Fe layers were found to be highly textured irrespective of the thickness of MgO layers. Energy dispersive X-ray microanalysis was used to observe intermixing at the interface of Fe and MgO layers.MgO tunneling barriers are extensively studied as a spin filtering and diffusion barrier for deposition of ferromagnetic layers on GaAs (001) surfaces. The relatively large lattice mismatch of the MgO and GaAs substrate and probable formation of interface states at the metal layer side require a careful barrier design. We present a study of deposition, microstructure, and strain relaxation in MgO barriers deposited on GaAs. The dependence of morphology of MgO layers on their thickness was characterized using a combination of X-Ray Reflectivity and High Resolution Transmission Electron Microscopy. The stress at the MgO/GaAs interface was observed to be released through the formation of misfit dislocations and partially by the formation of mis-oriented domains. The deposited MgO and Fe layers were found to be highly textured irrespective of the thickness of MgO layers. Energy dispersive X-ray microanalysis was used to observe intermixing at the interface of Fe and MgO layers.

We consider the Bragg effect in an in‐plane reflector realized with a field‐tuneable superlattice. The latter is induced via an interdigitated gate on a waveguide formed by a GaAs–AlAs quantum well system. In such a system the Bragg resonance arises from the laterally periodic modulation of the quantum confined Stark effect. The reflection coefficient is shown to be voltage tuneable, and the angular and frequency dependences are analyzed theoretically. We find that acceptable values of reflection can be achieved for frequencies close to the interband resonance. Furthermore, we point out that the in‐plane Bragg reflector can be used to study exciton–polariton coupling in semiconductor waveguides.

We study the tuneability of nanoholes created by local droplet etching of AlGaAs surfaces with Al droplets at varied coverage θ of the deposited droplet material and process temperature T. For the contact angle of the as-grown droplets a mean value of 66° is determined, which depends neither on θ nor on T. The experimental results on the hole structural characteristics are interpreted in terms of scaling models yielding a general form f(θ,T)∝θqexp(E/[kBT]), with constants q and E and Boltzmann's constant kB. In detail, the hole density varies from N = 4.0 × 106 up to 1.5 × 108 cm−2, and the scaling parameters are q = 0 and E = EN = 2.46 eV. The hole diameter varies from 50 up to 190 nm with scaling parameters q = 1/3 and E = −EN/3. Moreover, the hole depth varies from 9 up to 125 nm with q = 2/3 and E = −1.73 eV. Furthermore, a threshold coverage of at least 0.2 monolayers (ML) must be deposited before hole formation takes place. In situ electron diffraction indicates that these 0.2 ML are consumed for a ...

We study the formation of nanoholes and quantum rings in GaAs and AlGaAs surfaces by local droplet etching with InxGa1−x. The rings are crystallized from droplet material and surround the nanohole openings. In particular, the influence of the In content x on density, diameter, and depth of the nanoholes is investigated. Our data establish an exponential dependence of these quantities on x, which is quantitatively reproduced by a model that considers different surface diffusion energy barriers for Ga and In. By etching with pure In, hole densities as low as 5×106 cm−2 have been achieved. In addition, for low In content incompletely removed initial droplets are visible on the surface. These droplets are not visible on samples with x>0.5 which indicates a higher desorption rate of In compared to Ga. As a consequence, even in the case of etching with InGa the quantum rings consist of nearly pure GaAs. This is confirmed by photoluminescence experiments of quantum rings overgrown with AlGaAs barrier material.

We study the formation of nanoholes and quantum rings in GaAs and AlGaAs surfaces by local droplet etching (LDE) with Ga and In. The quantum rings are formed by the droplet etching process and surround the nanohole openings. Our data show that a low As pressure is essential for LDE and that process conditions with high Ga coverage yield formation of additional hillocks or large hills. With atomic force microscopy we establish that the amount of material removed from the nanoholes is equal to the amount of material stored in the quantum rings. Basing on the experimental observations, we propose a model of nanohole and quantum ring formation.