We study the electronic and optical properties of $\mathrm{In}\mathrm{As}∕\mathrm{In}\mathrm{P}$ quantum dots (QDs) on (100) and $\left(311\right)B$ substrates. Atomic force microscopy (AFM) and cross-sectional scanning tunneling microscopy (X-STM) are used to define the size and shape of the quantum dots for calculations. Eight-band $\mathbf{k}\mathbf{\bullet }\mathbf{p}$ calculations including strain and piezoelectric effects are then performed on such a structure for two different kinds of substrate orientation $\left(311\right)B$ and (100). Results for several QD heights found on $\left(311\right)B$ substrate fit well the experimental data obtained from photoluminescence measurements. On $\left(311\right)B$ substrate, the shear and hydrostatic deformations are found to be enhanced compared to those on (100) substrate thus affecting the electronic and optical properties. The $\left(311\right)B$ QDs are found to activate second-order ($S\text{−}P$ channels) transitions resulting from the complete loss of symmetry due to the presence of the piezoelectric field.

We present the fabrication and characterization of graphene-semiconductor-graphene ultraviolet photodetector based on the rectifying character of Schottky junction at the interface between epitaxial graphene and SiC semiconductor. As-grown single layer epitaxial graphene is interdigitated as transparent conductive electrode to probe photo-generated charge carriers in a semi-insulating 4H-SiC substrate. The fabricated device exhibits the typical current-voltage characteristics of a conventional metal-semiconductor-metal type photodetector with low leakage current. Time-resolved photocurrent measurements suggest an excellent photocurrent reversibility and high response speed of the device. The measurements performed for different illumination wavelengths showed that the sample reveals higher responsivity values when it is exposed to the light with 254 nm wavelength. The obtained results imply that epitaxial graphene can be used readily as transparent conductive electrode for SiC based optoelectronic device applications.

The impact of the capping material on the structural properties of self-assembled InAs quantum dots (QDs) was studied at the atomic scale by cross-sectional scanning tunneling microscopy. Capping with lattice matched layers and with strained layers was analyzed. When the different capping materials are lattice matched to the substrate, the differences in the QD properties can be dominated by chemical effects: InAs/InP QDs capped with InP have a 2 ML smaller height than those capped with InGaAs or InGaAsP due to As/P exchange induced decomposition. The height of the dots is found to be much more strongly affected when strained capping layers are used. InAs/GaAs, QDs capped with InGaAs are considerably taller than typical GaAs-capped dots. When GaAsSb is used as the capping layer, the dots are almost full pyramids with a height of 9.5 nm, indicating that dot decomposition is almost completely suppressed. This indicates that the dot/capping layer strain plays a major role in inducing dot decomposition during capping.

Cross-sectional scanning tunneling microscopy (STM) measurements on molecular beam epitaxy grown Mn doped GaAs(110) at 5 and 77 K are presented. The enhanced mechanical stability of the STM at low temperature allows a detailed study of the electronic contrast of Mn atoms in the GaAs(110) surface. According to reproducible and distinguishable contrast patterns of single Mn atoms, we present statistical evidence for a layer by layer identification of Mn atoms embedded in the first few monatomic layers of the crystal. A comparison with a bulklike theoretical approach reveals a semiquantitative agreement with the measurements. Remaining differences between theory and experiment indicate the influence of the surface as an important factor to understand the contrast of impurities close to the surface. Furthermore, we report the injection of transition-metal atoms into the surface. Finally, reproducible complexes consisting of a surface Mn and an adsorbate atom are found and manipulated.

Measurements of the local density of states of individual acceptors in III\char21{}V semiconductors show that the symmetry of the acceptor states strongly depends on the depth of the atom below a (110) surface. Tight-binding calculations performed for a uniformly strained bulk material demonstrate that strain induced by the surface relaxation is responsible for the observed depth-dependent symmetry breaking of acceptor wave functions. As this effect is strongest for weakly bound acceptors, it explains within a unified approach the commonly observed triangular shapes of shallow acceptors and the crosslike shapes of deeply bound acceptor states in III\char21{}V materials.

We have investigated the effect of a poly (3-hexylthiophene-2.5-diyl)(P3HT)–graphene bilayer electrode on the photoresponsivity characteristics of Si-based Schottky photodetectors. P3HT, which is known to be an electron donor and absorb light in the visible spectrum, was placed on CVD grown graphene by dip-coating method. The results of the UV–vis and Raman spectroscopy measurements have been evaluated to confirm the optical and electronic modification of graphene by the P3HT thin film. Current–voltage measurements of graphene/Si and P3HT–graphene/Si revealed rectification behavior confirming a Schottky junction formation at the graphene/Si interface. Time-resolved photocurrent spectroscopy measurements showed the devices had excellent durability and a fast response speed. We found that the maximum spectral photoresponsivity of the P3HT–graphene/Si photodetector increased more than three orders of magnitude compared to that of the bare graphene/Si photodetector. The observed increment in the photoresponsivity of the P3HT–graphene/Si samples was attributed to the charge transfer doping from P3HT to graphene within the spectral range between near-ultraviolet and near-infrared. Furthermore, the P3HT–graphene electrode was found to improve the specific detectivity and noise equivalent power of graphene/Si photodetectors. The obtained results showed that the P3HT–graphene bilayer electrodes significantly improved the photoresponsivity characteristics of our samples and thus can be used as a functional component in Si-based optoelectronic device applications.