The role of defects in the formation of local states induced by atoms adsorbed on a semiconductor surface

The generalized Anderson-Haldane band model of a semiconductor is used to consider the influence of quasi-localized electron states in the band gap on states induced by metal atoms adsorbed on the semiconductor surface. The formation of the Schottky barrier is discussed for low degrees of metal cover. Numerical calculations were performed for the metal-p-GaAs (110) system. Fiz. Tekh. Poluprovodn. 31, 1236–1241 (October 1997)     

States confined in the barriers of type-III HgTe/CdTe superlattices

We present a theoretical study of states quasi-localized in CdTe barriers of HgTe/CdTe superlattices. We show that the quasi-localization of both electrons and holes will lead to strong Coulomb interaction, and thus to the formation of excitons. It is further demonstrated that such quasi-localized states, including excitons, exhibit confinement effect similar to those of loclaized states in quantum wells.     

Recombination of point defects and their interaction with the surface in the course of the clusterization of these defects in Si

The growth kinetics of the {113} interstitial defects in n-and p-Si under in situ electron irradiation in a JEOL-1250 high-voltage electron microscope was analyzed in detail. The competing effects of the recombination of point defects and their interaction with the surface on the point-defect clusterization were considered. It is shown that the prevailing interaction of vacancies with the crystal surface is a consequence of the emergence of an energy barrier for the recombination of point defects in lightly doped Si crystals. Under these conditions, the drain of vacancies to the surface compensates for an increase in the crystal energy caused by the separation of the Frenkel pairs. It is assumed that a large difference between the growth rates of the {113} defects in n-Si and p-Si observed experimentally under the conditions when recombination is dominant is caused by a difference in the energy barriers for recombination. The barrier heights obtained correlate with the lattice-relaxation energy of a vacancy in various charge states.     

On the surface photovoltaic effect in a multivalley semiconductor in an external magnetic field

A theory of the photovoltaic effect in a semi-infinite multvalley semiconductor upon the absorption of polarized light at free carriers caused by the specular reflection and diffuse scattering of electrons at a film surface is developed by us. The kinetic Boltzmann equation in the approximation of time relaxation and boundary conditions, which determine the correlation between the distribution function of electrons reflected from a semi-infinite crystal surface and the distribution function of electrons incident onto a surface for the case of both specular reflection and diffuse scattering is used. The aforementioned takes into account the fact that the distribution function of electrons diffusely scattered from a surface depends only on their energy and is determined from the condition of total electron flux vanishing at the surface. Expressions for analyzing the spectral dependence of the current which is linearly dependent on the magnetic-field strength are obtained.     

Position-Controlled Functionalization of Vacancies in Silicon by Single-Ion Implanted Germanium Atoms

Special point defects in semiconductors have been envisioned as suitable components for quantum-information technology. The identification of new deep centers in silicon that can be easily activated and controlled is a main target of the research in the field. Vacancy-related complexes are suitable to provide deep electronic levels but they are hard to control spatially. With the spirit of investigating solid state devices with intentional vacancy-related defects at controlled position, the functionalization of silicon vacancies is reported on here by implanting Ge atoms through single-ion implantation, producing Ge-vacancy (GeV) complexes. The quantum transport through an array of GeV complexes in a silicon-based transistor is investigated. By exploiting a model based on an extended Hubbard Hamiltonian derived from ab initio results, anomalous activation energy values of the thermally activated conductance of both quasi-localized and delocalized many-body states are obtained, compared to conventional dopants. Such states are identified, forming the upper Hubbard band, as responsible for the experimental sub-threshold transport across the transistor. The combination of the model with the single-ion implantation method enables future research for the engineering of GeV complexes toward the creation of spatially controllable individual defects in silicon for applications in quantum information technology.     

Generation of bulk defects in some semiconductors by laser radiation in the transparency region of the crystal

Laser-stimulated dissociation of regions enriched with metal and redistribution of point defects in the bulk of a semiconductor crystal under the effect of infrared laser radiation (for photon energies lower than the band gap) were studied. It is shown that the defect-generation rate depends on the power density and wavelength of the laser radiation and on the impurity concentration. Two mechanisms of migration for the laser-induced defects were ascertained, and the activation energies for migration during laser irradiation and after irradiation was terminated were estimated.     

Alignment of Rod‐Shaped Single‐Photon Emitters Driven by Line Defects in Liquid Crystals

Arrays of liquid crystal defects—linear smectic dislocations—are used to trap semiconductor CdSe/CdS dot‐in‐rods which behave as single‐photon emitters. Measurements of the emission diagram are combined together with measurements of the emitted polarization of the single emitters. It is shown that the dot‐in‐rods are confined parallel to the linear defects to allow for a minimization of the disorder energy associated with the dislocation cores. It is demonstrated that the electric dipoles associated with the dot‐in‐rods, tilted with respect to the rods, remain oriented in the plane including the smectic linear defects and perpendicular to the substrate, most likely due to dipole/dipole interactions between the dipoles of the liquid crystal molecules and those of the dot‐in‐rods. Using smectic dislocations, nanorods can consequently be oriented along a unique direction for a given substrate, independently of the ligands' nature, without any induced aggregation, leading as well to a fixed azimuthal orientation for the dot‐in‐rods' dipoles. These results open the way for the fine control of nanoparticle anisotropic optical properties, in particular, fine control of single‐photon emission polarization.     

On the specific features of the density of states of epitaxial graphene formed on metal and semiconductor substrates

Analytical expressions for the local densities of states of epitaxial graphene formed on metal and semiconductor substrates are derived on unified grounds. The conditions of strong and weak graphene-substrate coupling are considered. It is shown that, in the case of strong coupling (the interaction of carbon atoms of graphene with the substrate is much stronger than that of carbon atoms with each other), the local density of states of graphene is close to the density of states of an individual carbon adatom on both metal and semiconductor substrates. In the opposite case of weak graphene-(semiconductor substrate) coupling (the interaction of carbon atoms of graphene with the substrate is much weaker than that of carbon atoms with each other), there is no gap in the local density of states of graphene, and the Dirac point is in the band gap of the semiconductor substrate and coincides in energy with the local level of the separated (individual) carbon adatom. Graphene formed on a metal substrate also exhibits a zero-gap density of states. The problem of the band gap induced in graphene by a semiconductor substrate is considered in the general case. It is shown that, depending on the relation between the parameters of the problem, either one or two band gaps overlapping in energy with the band gap of the substrate can exist in the spectrum of graphene. The dependence of the band gaps on the strength of the graphene-substrate interaction is constructed. Numerical estimations are performed for epitaxial graphene formed on 6H-SiC {0001} faces.     

Threshold condition of DFB semiconductor lasers by thelocal-normal-mode transfer-matrix method: correspondence to thecoupled-wave method

An analytical expression for the threshold condition of DFB semiconductor lasers is derived based on the local-normal-mode transfer-matrix method (TMM). The threshold condition is expressed in terms of an equivalent reflection coefficient of a DFB laser structure and a Bloch-wave propagation constant. It is shown that the TMM threshold condition can reproduce the one which is derived by the coupled-wave method (CWM) under certain conditions. It is also shown that the CWM can predict very accurately the spatially averaged values of the threshold modal gain and the detuning frequency which are obtained by the TMM if the coupling coefficient in the CWM is replaced by the TMM coupling coefficient     

铜锌锡硫带边电子结构及缺陷态的光学表征

利用吸收、光电流和光致发光等光谱表征并结合理论报道,分析了缺陷态丰富的铜锌锡硫半导体材料的光学带隙、带尾态和深浅杂质能级,揭示了Sn_Zn相关的缺陷态是影响铜锌锡硫带边电子结构的关键因素,其中高浓度的中性缺陷簇[2Cu_Zn+Sn_Zn]能导致带隙明显窄化,而离子性缺陷簇[Cu_Zn+Sn_Zn]是主要的深施主缺陷态,同时存在的大量带尾态引起带边相关的光致发光峰明显红移。贫铜富锌条件下,适当减少锡含量,可有效抑制与Sn_Zn相关的缺陷簇,并避免带隙的窄化。