[en] We report the characterization of a giant piezoresistance effect observed in a two-valley, two-dimensional electron system confined to an AlAs quantum well and patterned with anti-dot lattices of ∼1 µm period. The system exhibits a low-temperature piezoresistive gauge factor (the fractional change in resistance divided by the fractional change in the sample's length), which depends on the anti-dot lattice period and can be as high as 22 000. Via monitoring the resistance of a simple, 40 µm long Hall bar sample based on this system, we are readily able to measure strain values down to 10⁻⁸ or, equivalently, length changes of the order of 1/100 of the Bohr radius

[en] The authors report a spatial control of the band gap in InGaAs/GaAs quantum dots (QDs) using the combined effects of pulsed excimer laser irradiation and impurity-free dielectric cap induced intermixing technique. A large band gap shift of up to 180 meV has been obtained under laser irradiation of 480 mJ/cm² and 150 pulses to the SiO₂ capped shallow QD structure, while the nonirradiated SiO₂ and Si_xN_y capped QDs only exhibit band gap shifts of 18 and 91 meV, respectively

[en] The impact of group-III vacancy diffusion, generated during dielectric cap induced intermixing, on the energy state transition and the inhomogeneity reduction in the InGaAs/GaAs quantum-dot structure is investigated. We use a three-dimensional quantum-dot diffusion model and photoluminescence data to determine the thermal and the interdiffusion properties of the quantum dot. The band gap energy variation related to the dot uniformity is found to be dominantly affected by the height fluctuation. A group-III vacancies migration energy H_m for InGaAs quantum dots of 1.7 eV was deduced. This result is similar to the value obtained from the bulk and GaAs/AlGaAs quantum-well materials confirming the role of SiO₂ capping enhanced group-III vacancy induced interdiffusion in the InGaAs quantum dots

[en] A brief report on the final round of the first World Physics Olympiad (WoPhO) held in Lombok, West Nusa Tenggara, Indonesia is presented. The theoretical and experimental problems are presented and the mark distribution is discussed. (paper)