Investigation of defect modes in a defective photonic crystal with a semiconductor metamaterial defect

In this work, we theoretically investigate the properties of defect modes in a defective photonic crystal containing a semiconductor metamaterial defect. We consider the structure, (LH)^N/D^P/(LH)^N, where N and P are respectively the stack numbers, L is SiO₂, H is InP, and defect layer D is a semiconductor metamaterial composed of Al-doped ZnO (AZO) and ZnO. It is found that, within the photonic band gap, the number of defect modes (transmission peaks) will decrease as the defect thickness increases, in sharp contrast to the case of using usual dielectric defect. The peak height and position can be changed by the variation in the thickness of defect layer. In the angle-dependent defect mode, its position is shown to be blue-shifted as the angle of incidence increases for both TE and TM waves. The analysis of defect mode provides useful information for the design of tunable transmission filter in semiconductor optoelectronics.     

Josephson current through a ferromagnetic semiconductor/semiconductor/ferromagnetic semiconductor structure

We theoretically calculate the Josephson current for two superconductor/ferromagnetic semiconductor (SC/FS) bilayers separated by a semiconductor (SM) layer. It is found that the critical Josephson current I_C in the junction is strongly determined by not only the relative orientations of the effective exchange field of the two bilayers and scattering potential strengths at the interfaces but also the kinds of holes (the heavy or light) in the two FS layers. Furthermore, a robust approach to measuring the spin polarization P for the heavy and light holes is presented.     

Kinetics of the surface charging of a semiconductor during adsorption

The kinetic characteristics of the surface charging of a semiconductor during adsorption are analyzed, due allowance being made for the recharging of the biographic surface states during the adsorption process. It is shown that the form of the kinetic curves depends very substantially on the relationship between the characteristic relaxation times of the adsorption and biographic surface states.     

Theory of defect complexes at semiconductor surfaces

We report calculations of deep levels associated with defect complexes at semiconductor surfaces. For the antistructure defect (As_Ga, Ga_As) at the (110) surface of GaAs, the results are qualitatively the same as the sum of those for the individual antisite defects As_Ga and Ga_As — a donor level and two acceptor levels within the band gap.     

Coherent transfer of spin through a semiconductor heterointerface

Spin transport between two semiconductors of widely different band gaps is time resolved by two-color pump-probe optical spectroscopy. Electron spin coherence is created in a GaAs substrate and subsequently appears in an adjacent ZnSe epilayer at temperatures ranging from 5 to 300 K. The data show that spin information can be protected by transport to regions of low spin decoherence, and regional boundaries used to control the resulting spin coherent phase.     

Selective high-resolution electrodeposition on semiconductor defect patterns

We report a new principle and technique that allows one to electrodeposit material patterns of arbitrary shape down to the submicrometer scale. We demonstrate that an electrochemical metal deposition reaction can be initiated selectively at surface defects created in a p-type Si(100) substrate by Si (++) focused ion beam bombardment. The key principle is that, for cathodic electrochemical polarization of p-type material in the dark, breakdown of the blocking Schottky barrier at the semiconductor/electrolyte interface occurs at significantly lower voltages at implanted locations than for an unimplanted surface. This difference in the threshold voltages is exploited to achieve selective electrochemical deposition.     

Spin-polarized transport through a time-periodic non-magnetic semiconductor heterostructure

Spin-dependent Floquet scattering theory is developed to investigate the photon-assisted spin-polarized electron transport through a semiconductor heterostructure in the presence of an external electric field. Spin-dependent Fano resonances and spin-polarized electron transport through a laser irradiated time-periodic non-magnetic heterostructure in the presence of Dresselhaus spin-orbit interaction and a gate-controlled Rashba spin-orbit interaction are investigated. The electric field due to laser along with the spin-orbit interactions help to get spin-dependent Fano resonances in the conductance, whereas the external bias can be appropriately adjusted to get a near 80% spin-polarized electron transmission through heterostructures. The resultant nature of the Floquet scattering depends on the relative strength of these two electric fields.     

Higher-order amplitude squeezing of photons propagating through a semiconductor

Kth power photon amplitude squeezing is studied when the coherent photon propagates through a semiconductor containing the exciton. If the exciton is prepared initially in a coherent state, the photon may become Kth power amplitude squeezed. It is shown that, in the short-time limit, the photon squeezing in the P direction does not appear at all while that in the X direction is possible for all the amplitude powers K. In the latter case, the amount of squeezing is larger for higher power K. The dependences on all the system parameters as well as on the output light detection moment are investigated in detail.     

Continuous-wave Raman laser pumped within a semiconductor disk laser cavity

A KGd(WO?)? Raman laser was pumped within the cavity of a cw diode-pumped InGaAs semiconductor disk laser (SDL). The Raman laser threshold was reached for 5.6 W of absorbed diode pump power, and output power up to 0.8 W at 1143 nm, with optical conversion efficiency of 7.5% with respect to the absorbed diode pump power, was demonstrated. Tuning the SDL resulted in tuning of the Raman laser output between 1133 and 1157 nm.     

Possible lattice formation of new materials within a piezoelectric semiconductor plasma

The possible lattice formation of grains of chosen material in a magnetized current carrying n-type piezoelectric semiconductor plasma has been examined. In addition to the repulsive Coulomb potential, there appears a non-Coulombic oscillatory potential among the highly charged grains due to the strong resonant collective interaction of the grains and the electron-acoustic mode of the host semiconductor giving rise to the possibility of the lattice formation of grains of new materials.     

Quantum conductance through a uniform scatterer in a narrow-wire semiconductor

The quantum conductance for electrons scattering from a uniform scatterer in a narrow-wire semiconductor is calculated. Instead of getting the conductance directly from the calculation of transmission coefficient, we calculate the reflection coefficient instead. The transmission coefficient is then calculated by using the conservation law, T=I−R. This alternative method can avoid the instability of the conductance obtained by including more evanescent modes for a finite-range scatterer in a narrow-wire semiconductor. This method is applied to a semi-infinite strip potential barrier and a rectangular potential barrier in a narrow wire. The quantum stepwise conductance is obtained in both cases. For a repulsive rectangular potential barrier, there are oscillations in each stepwise conductance. For an attractive rectangular potential barrier, there exist multiple quasi-bound states below the sub-band energies which can cause the drop of the quantum conductance. The effect of the continuum quasi-bound states diminishes as the energy of the incident electron increases, but the influence of the discrete quasi-bound states still persists.     

Influence of oxygen adsorption on the surface potential of a metal oxide semiconductor

Analytical expressions describing dependences of the surface density of adsorbed oxygen ions and energy band bending in the subsurface region of a metal oxide semiconductor on the oxygen concentration that consider not only the process of neutral gas particle adsorption, but also their charge transfer at the expense of electron capture from the conduction band are presented. It is demonstrated that the heat of oxygen ion absorption is equal to the sum of the heat of neutral particle adsorption and the energy gap between the Fermi level and the level of the oxygen ion on the semiconductor surface. When the adsorption equilibrium is established, an analytical expression describing the time dependence of the energy band bending can be obtained only for small change of the oxygen concentration in the gas mixture.     

A mid-infrared tunable filter in a semiconductor-dielectric photonic crystal containing doped semiconductor defect

In this work, we theoretically analyze tunable filtering properties in a semiconductor-dielectric photonic crystal (SDPC) containing doped semiconductor defect in the mid-infrared frequency region. We consider two possible configurations of filter structures, the symmetric and asymmetric ones. With a defect of the doped n-type semiconductor, n-Si, the resonant transmission peak can be tuned by varying the doping concentration, that is, the peak wavelength will be shifted to the position of lower wavelength for both structures. Additionally, by increasing the defect thickness, it is also possible to have a filter with multiple resonant peaks, leading to a multichannel filter. The results provide another type of tunable filter in the defective SDPC that could be of technical use for semiconductor applications in optical electronics.     

Effect of adsorption on the surface mobility of charge carriers in a semiconductor substrate

The effect of adsorption on the carrier mobility in the near-surface region of a semiconductor substrate has been investigated within the framework of the Schrieffer model. The dependence of the carrier surface mobility on the concentration of adatoms has been determined. The systems chosen for the study are the gases adsorbed on the surface of semiconductor oxides. Empirical estimates of the surface mobility, which are based on modification of conventional volume scattering mechanisms, have been proposed.     

Current bistability in resonant tunneling through a semiconductor quantum dot

We discuss resonant tunneling through quantum dot energy levels considering the charging energy of the dot. The hamiltonian of the system is reduced to a form of the Anderson hamiltonian of resonant tunneling. The mean-field approximation is applied and current–voltage characteristics are evaluated. The self-consistent solution is investigated for the low tunneling rate case in the low-temperature condition. The current bistability and the related current hysteresis are pointed out. The Coulomb staircase is shown in the current–voltage characteristics. These features are all due to Coulomb repulsion within the dot.     

Persistent current through a semiconductor quantum dot with Gaussian confinement

The persistent diamagnetic current in a GaAs quantum dot with Gaussian confinement is calculated. It is shown that except at very low temperature or at high temperature, the persistent current increases with decreasing temperature. It is also shown that as a function of the dot size, the diamagnetic current exhibits a maximum at a certain confinement length. It is furthermore shown that for a shallow potential, the persistent current shows an interesting maximum structure as a function of the depth of the potential. At low temperature, the peak structure is pretty sharp but becomes broader and broader with increasing temperature.     

半导体激光器光束准直系统的功率耦合效率

在长距离无线光通信中，接收点光功率密度与光束发散角平方呈反比关系，为了获得小的发散角和大的功率耦合效率，要求准直系统有较大的数值孔径(NA)，但数值孔径过大会增加像差，因此合理设计功率耦合效率与准直系统的数值孔径就非常重要。该文对半导体激光器光束准直系统中功率耦合效率进行了研究，给出了半导体激光器光束功率耦合效率与k(孔径半径与孔径处等效光束半径之比)的关系表达式，并结合激光器光束准直系统，给出了半导体激光器光束功率耦合效率与准直系统数值孔径的关系表达式。该研究结论对于半导体激光器光束准直系统设计具有参考作用。     

Direct observation of localized defect States in semiconductor nanotube junctions

We report scanning tunneling microscopy of semiconductor-semiconductor carbon nanotube junctions with different band gaps. Characteristic features of the wave functions at different energy levels, such as a localized defect state, are clearly exhibited in the atomically resolved scanning tunneling spectroscopy. The peaks of the Van Hove singularity on each side penetrate and decay into the opposite side across the junction over a distance of approximately 2 nm. These experimental features are accounted for, with the help of tight-binding calculation, by the presence of pentagon-heptagon pair defects at the junction.