Narrow Results

Epitaxial layers of ZnTe have been grown on a (111) oriented CdTe single crystal substrate by thermal evaporation technique at 180°C and a pressure of 10^-6 Torr. X-ray diffraction pattern indicated a highly oriented crystallographic growth of ZnTe (111) layer on CdTe (111) substrate. C–V measurements are carried out at frequencies of 10 kHz and 100 kHz. 1/C² versus the forward bias voltage gave a straight line in the voltage range from 1 to 3 V. Extrapolation of 1/C² → 0 led to an estimated value of the built-in potential of about 0.58 V. The calculated charge carrier concentration in the lightly doped over-grown layer, ZnTe, has been found to be p = 1.7 × 10¹⁶cm^-3. It was found that energy band diagram constructed according to the electron affinity model is not the adequate one to explain the capacitance–voltage behavior. Therefore, one should take into account the effect of interface states on the energy band diagram. The interface states density has been estimated to be ~10¹³cm^-2 for (111) ZnTe/(111)CdTe heterojunction system. The interface states were identified as hole traps for the ZnTe/CdTe heterojunction. Accordingly, a band bending downward both materials, and a depletion zone in both of them are expected.

We review how broken symmetries affect optical properties in photonic analog of graphene, namely, honeycomb-lattice photonic crystals (PhCs). The spatial symmetry of the honeycomb lattice yields Dirac spectra at Brillouin zone corners without fine tuning of physical parameters. In addition, the "Dirac-mass" gap can be introduced by breaking the time-reversal symmetry and/or the space-inversion symmetry. These two symmetries are closely related to the topology of radiation fields in momentum space, and are linked with nontrivial edge states if the system has edges. We show that an effective Hamiltonian for photon obtained with the aid of group theory predicts a modulation of chiral edge states that are hardly implemented in electronic graphene. Numerical simulation of the honeycomb-lattice PhCs of infinitely-long cylinders, confirms the prediction fairly well.

Due to the mismatch between ZnO film and $p$-Si lattice, there are a large number of interface states which seriously affect the photoelectric properties of ZnO/$p$-Si heterojunction optoelectronic devices. In this research, ZnO thin films were deposited on $p$-Si by magnetron sputtering and ZnO/$p$-Si heterojunction was prepared. CuSCN film buffer layer was inserted into the interface of ZnO/$p$-Si heterojunction to reduce the interface state and improve the electric properties of heterojunction. The results show that the insertion of CuSCN films can effectively improve the interface state of ZnO/$p$-Si heterojunction, increase the forward current, reduce the reverse current and improve the heterojunction rectification ratio.

The interface state in two-dimensional (2D) sonic crystals (SCs) was obtained based on trying or cutting approach, which greatly limits its practical applications. In this paper, we theoretically demonstrate that one category of interface states can deterministically exist at the boundary of two square-lattice SCs due to the geometric phase transitions of bulk bands. First, we derive a tight-binding formalism for acoustic waves and introduce it into the 2D case. Furthermore, the extended 2D Zak phase is employed to characterize the topological phase transitions of bulk bands. Moreover, the topological interface states can be deterministically found in the nontrivial bandgap. Finally, two kinds of SCs with the $C_{4v}$ symmetry closely resembling the 2D Su–Schrieffer–Heeger (SSH) model are proposed to realize the deterministic interface states. We find that tuning the strength of intermolecular coupling by contacting or expanding the scatterers can effectively induce the bulk band inversion between the trivial and nontrivial crystals. The presence of acoustic interface states for both cases is further demonstrated. These deterministic interface states in 2D acoustic systems will be a great candidate for future waveguide applications.

Stimulated emission has been observed from oxide structure of silicon when optically excited by 514 nm laser. The twin peaks in the region from 690 nm to 700 nm are dominated by stimulated emission which can be demonstrated by its threshold behavior and transition in linear evolution. The oxide structure was fabricated by laser irradiation and annealing treatment on silicon. A model for explaining the stimulated emission has been proposed in which the trap states of the interface between oxide of silicon and porous nanocrystal play an important role.

We have fabricated SnO₂/p-Si and SnO₂/p-PoSi heterojunction diodes by spray pyrolysis method. To prepare porous Si substrates, the etching time was varied from 10 to 20 and 30 mins. In these samples, the SEM micrographs showed a distributed pore areas surrounded by columnar walls with various height. The data analysis of the rectified I–V characteristic, using thermionic emission Schottky diode theory, showed that although the barrier height is about 0.5–0.6 eV in all samples other two important diode parameters, i.e. the ideality factor n and the series resistance r_s, are strongly etching time-dependant and are increased with increasing the etching time.

In this paper, Dirac point method is used to study the interface state of one-dimensional photonic crystal heterojunction ${[{(AB)}_m{(CD)}_m]}_n$ containing dispersive materials GaAs. We found that the energy levels of the interface states satisfy a simple sinusoidal function. We investigate the variation of the energy levels of the interface states with the incident angle, it is found that these interface states move toward high-frequency with the increase of the incident angle. At the same time, it is found that there is an extra localized band and it is further proved that the extra band corresponds to the defect band, and the energy levels of the defect band possess the same behavior with those of interface states.

Pd/Si_0.9Ge_0.1/Si Schottky barrier diodes subjected to irradiation are characterized using capacitance and conductance measurements performed under forward and reverse bias while varying the temperature and frequency. The C–V technique has been used in particular to determine the carriers profile as well as the interface state density and its energy distribution.

The chemical etching of the surface of silicon wafers is a critical step in the manufacturing process of all semiconductor devices. In this contribution, we investigate the effect of alkaline etching on minority carrier lifetime and interface-states density ($D_{\mathrm{\text{it}}})$ of silicon wafers intended to be used as solar cell substrates. After alkali treatment, the surface morphology was analyzed using scanning electron microscopy (SEM) and UV-visible-NIR optical spectroscopy. Besides and as electrical characterizations, the minority charge carrier lifetime (${\tau }_{\mathrm{\text{n}}})$ was measured by the Quasi-Steady State Photoconductance technique (QSSPC), and the Electrochemical Impedance Spectroscopy was used to evaluate $D_{\mathrm{\text{it}}}$. These results were correlated with the surface recombination velocity (SRV) calculated by fitting the experimental data to the theory. The results of characterization showed a lower SRV and a higher apparent lifetime (${\tau }_{\mathrm{\text{app}}})$ obtained with 23wt.% KOH etching as compared to those obtained with 30wt.% NaOH; viz. 825cm$\cdot {\mathrm{\text{s}}}^{-1}$ against 1500cm.s${}^{-1}$ and 32$\mu$s against 23$\mu$s, respectively. These findings were corroborated by $D_{\mathrm{\text{it}}}$ measurements which gave $1.55\times 10^{11}$ev${}^{-1}$cm${}^{-2}$ for KOH treatment and $5.67\times 10^{12}$ev${}^{-1}$cm${}^{-2}$ for NaOH treatment.