The strain distribution in and around pyramidal InAs/GaAs quantum dots (QD’s) on a thin wetting layer fabricated recently with molecular-beam epitaxy, is simulated numerically. For comparison analytical solutions for the strain distribution in and around a pseudomorphic slab, cylinder, and sphere are given for isotropic materials, representing a guideline for the understanding of strain distribution in two-, one-, and zero-dimensional pseudomorphic nanostructures. For the pyramidal dots we find that the hydrostatic strain is mostly confined in the QD; in contrast part of the anisotropic strain is transferred from the QD into the barrier. The optical-phonon energies in the QD are estimated and agree perfectly with recent experimental findings. From the variation of the strain tensor the local band-gap modification is calculated. Piezoelectric effects are additionally taken into account. The three-dimensional effective-mass single-particle Schrödinger equation is solved for electrons and holes using the realistic confinement potentials. Since the QD’s are in the strong confinement regime, the Coulomb interaction can be treated as a perturbation. The thus obtained electronic structure agrees with luminescence data. Additionally AlAs barriers are considered.

We present a systematic investigation of the elastic, electronic, and linear optical properties of quantum dot double heterostructures in the frame of eight-band $\mathbf{k}\cdot \mathbf{p}$ theory. Numerical results for the model system of capped pyramid shaped InAs quantum dots in GaAs (001) with $\{101\}$ facets are presented. Electron and hole levels, dipole transition energies, oscillator strengths, and polarizations for both electron-hole and electron-electron transitions, as well as the exciton ground-state binding energy and the electron ground-state Coulomb charging energy are calculated. The dependence of all these properties on the dot size is investigated for base widths between 10 and $20$ nm. Results for two different approaches to model strain, continuum elasticity theory, and the Keatings valence force field model in the linearized version of Kane, are compared to each other.

Low threshold, large T_o injection laser emission via zero-dimensional states in (InGa)As quantum dots is demonstrated. The dots are formed due to a morphological transformation of a pseudomorphic In_0.5Ga_0.5As layer. Laser diodes are fabricated with a shallow mesa stripe geometry.

High-precision gas sensors operated at room temperature are attractive for various real-time gas monitoring applications, with advantages including low energy consumption, cost effectiveness and device miniaturization/flexibility. Studies on sensing materials, which play a key role in good gas sensing performance, are currently focused extensively on semiconducting metal oxide nanostructures (SMONs) used in the conventional resistance type gas sensors. This topical review highlights the designs and mechanisms of different SMONs with various patterns (e.g. nanoparticles, nanowires, nanosheets, nanorods, nanotubes, nanofilms, etc.) for gas sensors to detect various hazardous gases at room temperature. The key topics include (1) single phase SMONs including both n-type and p-type ones; (2) noble metal nanoparticle and metal ion modified SMONs; (3) composite oxides of SMONs; (4) composites of SMONs with carbon nanomaterials. Enhancement of the sensing performance of SMONs at room temperature can also be realized using a photo-activation effect such as ultraviolet light. SMON based mechanically flexible and wearable room temperature gas sensors are also discussed. Various mechanisms have been discussed for the enhanced sensing performance, which include redox reactions, heterojunction generation, formation of metal sulfides and the spillover effect. Finally, major challenges and prospects for the SMON based room temperature gas sensors are highlighted.

We report ultranarrow $(<0.15\mathrm{}\mathrm{meV})$ cathodoluminescence lines originating from single InAs quantum dots in a GaAs matrix for temperatures up to 50 K, directly proving their $\delta$-function-like density of electronic states. The quantum dots have been prepared by molecular beam epitaxy utilizing a strain-induced self-organizing mechanism. A narrow dot size distribution of width $12\pm 1\mathrm{nm}$ is imaged by plan-view transmission electron microscopy. Cathodoluminescence images directly visualize individual dot positions and recombination from a single dot. A dense dot array $(\sim {10}^{11}\mathrm{dots}/{\mathrm{cm}}^2)$ gives rise to a distinct absorption peak which almost coincides with the luminescence maximum.

Polarized micro-Raman measurements were performed to study the phonon modes of Fe, Sb, Al, Ga, and Li doped ZnO thin films, grown by pulsed-laser deposition on $c$ -plane sapphire substrates. Additional modes at about 277, 511, 583, and $\text{644\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}},$ recently assigned to N incorporation [A. Kaschner et al., Appl. Phys. Lett. 80, 1909 (2002)], were observed for Fe, Sb, and Al doped films, intentionally grown without N. The mode at $\text{277\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ occurs also for Ga doped films. These modes thus cannot be related directly to N incorporation. Instead, we suggest host lattice defects as their origin. Further additional modes at 531, 631, and $\text{720\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ seem specific for the Sb, Ga, and Fe dopants, respectively. Li doped ZnO did not reveal additional modes.