N-doped Semiconductor Research Articles

Giant Kerr nonlinearity in an n-doped semiconductor quantum well

A scheme for enhancement of Kerr nonlinearity with vanishing linear and nonlinear absorption in a three-level ladder-configuration n-doped semiconductor quantum well is proposed. It is shown that the Kerr nonlinearity can be controlled and even enhance by the intensity of coupling fields. Also, phase control of Kerr nonlinearity is then discussed.

Chemisorption on semiconductors: The role of quantum corrections on the space charge regions in multiple dimensions

The chemisorption of O2 on nanoscale n-doped CdS semiconductors is computed in terms of a Wolkenstein isotherm coupled to the Schrödinger Poisson equation. Present numerical results show the dependence of the chemisorbed charge and the differential capacitance on oxygen partial pressure. A comparison against the classical Poisson-Boltzmann approach shows a higher chemisorbed charge in the quantum model, but a greater differential capacitance in the classical case.

Influence of the spin–orbit interaction in the impurity-band states of n-doped semiconductors

We study numerically the effects of an extrinsic spin–orbit interaction on the model of electrons in n-doped semiconductors of Matsubara and Toyozawa (MT). We focus on the analysis of the density of states (DOS) and the inverse participation ratio (IPR) of the spin–orbit perturbed states in the MT set of energy eigenstates in order to characterize the eigenstates with respect to their extended or localized nature. The finite sizes that we are able to consider necessitate an enhancement of the spin–orbit coupling strength in order to obtain a meaningful perturbation. The IPR and DOS are then studied as a function of the enhancement parameter.

The role of excitons and trions on electron spin polarization in quantum wells

We have studied the time evolution of the electron spin polarization under continuous photoexcitation in remotely n-doped semiconductor quantum wells. The doped region allows us to get the necessary excess of free electrons to form trions. We have considered electron resonant photoexcitation at free, exciton, and trion electron energy levels. Also, we have studied the relative effect of photoexcitation energy density and doping concentration. In order to obtain the two-dimensional density evolution of the different species, we have performed dynamic calculations through the matrix density formalism. Our results indicate that photoexcitation of free electron level leads to a higher spin polarization. Also, we have found that increasing the photoexcitation energy or diminishing the doping enhances spin polarization.

Transient two-photon absorption property in a n-doped semiconductor quantum well

We investigate the transient two-photon absorption property in a n-doped three-level semiconductor quantum well system. It is shown that the intensities and detunings of the optical fields can affect the two-photon absorption spectra dramatically, which can be used to suppress or enhance the two-photon absorption coefficient. The dependence of two-photon absorption property on the relative phase of three optical fields is also discussed. Our study is much more practical than its atomic counterpart due to its flexible design and new characters. Thus, it may provide some new possibilities for technological applications.

Band energy structure calculations and spin effect in zinc-blende semiconductors

Band energy structure of the n-doped zinc-blende semiconductor was calculated using norm-conserving pseudopotential and Green function methods. The calculations for the semiconductor with different dopant contents were performed in the presence of external circularly polarized axial and polar dc-field potentials. Changes in the spin density distribution for the clusters with different dopant concentrations and at different lattice temperatures and an enhancement of the spin-polarized delocalization states in the presence of the dc-field potential were observed. The observed photo-induced spin effects were explained within a framework of the band energy model of spin physics of taking into account of the photo-induced electron–phonon anharmonicity. The results are consistent with those obtained in experiments of photospintronics.

TERAHERTZ METAMATERIAL MODULATORS BASED ON ABSORPTION

Metamaterial absorbers can perfectly absorb an incident wave in a narrow frequency band. In this paper, metamaterial absorbers are used to construct a terahertz modulator. By controlling the carrier density in the n-doped semiconductor spacer between a patterned metallic superstructure and a metallic ground with different applied voltage bias, the absorption varies sensitively, and the reflected wave amplitude acting as the modulated signal can be strongly modulated. Two types of modulators are investigated, one of which possesses an array of metallic crosses as the superstructure, and the other has a complementary superstructure. Compared with the former, the latter may give a better modulation performance.

The Theoretical Study of Semiconductor-Bridge Dynamic Resistance

The semiconductor bridge (SCB) is a heavily n-doped semiconductor. The SCB device has advantages for reducing voltage and energy requirements compared with a conventional device. It also has very excellent safety. When driven with a short low-energy pulse, the SCB creates hot plasma to ignite energetic materials. The hot plasma permeates the energetic materials and deposits its latent heat of fusion to the grains, thereby heating the granular surfaces to energy states required for self-sustained reaction. The behavior of the SCB can be facilitated through the simulation of the electrical components. The resistance of the SCB is a key parameter during the process of producing the plasma. The dynamic resistance of a heavily doped semiconductor resistor was evaluated by observing the electrical mobility and conductivity of the resistor as a function of temperature covering the range from room temperature to the plasma temperature. In an effort to elucidate the dynamic resistance of the SCB, current was forced to flow through the bridge with an initial resistance of 1 Ω. The energy stored in a 25-μF capacitor was used to activate the plasma. Two peaks in the voltage-time curve were typically observed. Time histories of the resistance and voltage show the special features of the resistor. It appears that the resistance increases initially before the intrinsic temperature and then decreases due to negative resistance behavior, and then, the resistor is melted and vaporized to generate plasma.

Transient gain-absorption properties of the probe field in a semiconductor quantum well

We investigate the transient gain-absorption properties of the probe field in an n-doped three-level semiconductor quantum well system. It is shown that the coupling field and the pumping field affect the optical behavior dramatically, which can be used to manipulate the gain-absorption coefficient. The dependence of the gain-absorption properties on the relative phase is also discussed. Our study is much more practical than its atomic counterpart due to its flexible design and the wide adjustable parameters. Thus, it may provide some new possibilities for technological applications.

Evolution kinetics of nonequilibrium longitudinal-optical phonons generated by drifting electrons in III-nitrides: longitudinal-optical-phonon resonance

The case of n-doped direct gap polar semiconductors in the presence of moderate to high electric fields is considered. The study is centered on the theoretical analysis of the behavior of LO phonons generated by drifting electrons. The emergence of a kind of “resonance” (or “overheating”) in the LO-phonon distribution which is centered on an off-center region of the Brillouin zone is evidenced. It consists in a preferential concentration of nonthermal populations of LO phonons in the form of a lobular distribution with its axis along the direction of the electric field. Numerical calculations performed for the case of strongly polar GaN accompanied with descriptive figures are presented.

Synthesis and Electronic Properties of the Misfit Layer Compound [(PbSe)1.00]1[MoSe2

An ultralow-thermal-conductivity compound with the ideal formula [(PbSe)1.00]1[MoSe2]1 has been successfully crystallized across a range of compositions. The lattice parameters varied from 1.246 nm to 1.275 nm, and the quality of the observed 00l diffraction patterns varied through the composition region where the structure crystallized. Measured resistivity values ranged over an order of magnitude, from 0.03 Ω m to 0.65 Ω m, and Seebeck coefficients ranged from −181 μV K−1 to 91 μV K−1 in the samples after the initial annealing to form the basic structure. Annealing of samples under a controlled atmosphere of selenium resulted in low conductivities and large negative Seebeck coefficients, suggesting an n-doped semiconductor. Scanning transmission electron microscopy cross-sections confirmed the interleaving of bilayers of PbSe with Se-Mo-Se trilayers. High-angle annular dark-field images revealed an interesting volume defect, where PbSe grew through a region where a layer of MoSe2 would be expected in the perfect structure. Further studies are required to correlate the density of these defects with the observed electrical properties.

Magnetism in armchair BC2N nanoribbons

We show by first-principles calculations that H-terminated armchair BC2N nanoribbons (a-BC2NNRs) have exceptional electronic and magnetic properties. In particular, a-BC2NNRs with the B and N atoms uncoordinated can be either p- or n-doped semiconductors, and the wide ones own spontaneous magnetization. It is shown that the magnetism is induced by the localization of acceptor or donor levels from unpaired B or N atoms, and the magnetic moment increases with further increasing ribbon width. The a-BC2NNRs with B and N atoms coordinated have band gaps decreasing with increasing ribbon width.

Cooling power of field emission from the n-type silicon semiconductor

The authors have theoretically investigated the cooling effect of field emission from n-type semiconductors. By considering the outgoing and incoming electrons in the region of emission, they make the numerical calculation of the energy exchange per field electron. It is found that even though the Joule heat is taken into account, the energy exchange is large enough for cooling the cathode. The cooling power sufficient for microelectronic device is obtained for field emission from the highly n-doped Si semiconductor.

Suppressed Blinking Dynamics of Single QDs on ITO

The exciton quenching dynamics of single CdSe/CdS(3ML)ZnCdS(2ML)ZnS(2ML) core/multishell QDs adsorbed on glass, In2O3, and ITO have been compared. Single QDs on In2O3 show shorter fluorescence lifetimes and higher blinking frequencies than those on glass because of interfacial electron transfer from QDs to In2O3. Compared to glass and In2O3, single QDs on ITO show suppressed blinking activity as well as reduced fluorescence lifetimes. For QDs in contact with the n-doped ITO, the equilibration of their Fermi levels leads to the formation of negatively charged QDs. In these negatively charged QDs, the off states are suppressed because of the effective removal of the valence band holes, and their fluorescence lifetimes are shortened because of exciton Auger recombination and hole transfer processes involving the additional electrons. This study shows that the blinking of single QDs can be effectively suppressed on the surface of ITO. This phenomenon may also be observable for other QDs and on different n-doped semiconductors.

Transmission interference tuned by an external static magnetic field in a two-slit structure

We present a near-field analysis of transmitted field interference tuned by an external static magnetic field on an n-doped semiconductor film drilled by two slits at terahertz frequency. It is found that the peak magnetic field intensity of the interference pattern between the two slits can be strengthened twice as against that of zero external static magnetic field. The physical origin comes from the interaction between surface plasmon polaritons (SPPs) and radiative evanescent field components launched by each slit on the transmitted surface, and also from the considerable alteration of the SPPs, caused by the external static magnetic field.

Self-sustained current oscillations in the kinetic theory of semiconductor superlattices

We present the first numerical solutions of a kinetic theory description of self-sustained current oscillations in n-doped semiconductor superlattices. The governing equation is a single-miniband Boltzmann–Poisson transport equation with a BGK (Bhatnagar–Gross–Krook) collision term. Appropriate boundary conditions for the distribution function describe electron injection in the contact regions. These conditions seamlessly become Ohm’s law at the injecting contact and the zero charge boundary condition at the receiving contact when integrated over the wave vector. The time-dependent model is numerically solved for the distribution function by using the deterministic Weighted Particle Method. Numerical simulations are used to ascertain the convergence of the method. The numerical results confirm the validity of the Chapman–Enskog perturbation method used previously to derive generalized drift-diffusion equations for high electric fields because they agree very well with numerical solutions thereof.

Nonlinear ultrafast modulation of the optical absorption of intense few-cycle terahertz pulses inn-doped semiconductors

We use an open-aperture Z-scan technique to show how intense few-cycle terahertz pulses can experience a nonlinear bleaching of absorption in an n-doped semiconductor due to terahertz-electric-field-driven intervalley scattering of electrons in the conduction band. Coherent detection of the transmitted terahertz pulse waveform also allows the nonlinear conductivity dynamics to be followed with sub-picosecond time resolution. Both the Z-scan and time-domain results are found to be in agreement with our theoretical analysis.

Optical transmission resonances tuned by external static magnetic field in an n-doped semiconductor grating with subwavelength slits

Transmission behavior of light through a grating consisting of n-doped semiconductor with subwavelength slits under the application of external static magnetic fields is investigated. As dielectric constant of n-doped semiconductor can be substantially altered by applied magnetic field, in the Voigt configuration and for TM-polarized illumination, two transmission resonance peaks associated with localized waveguide modes of slits are significantly shifted toward the lower frequency regime with the increase of the applied magnetic field. These characteristics can be assigned to a reduction of effective plasma frequency of n-doped semiconductor under the applied magnetic field. Our findings may provide possibility for achieving tunable transmission resonance spectrum.

Drift-diffusion crossover and the intrinsic spin diffusion lengths in semiconductors

We study the propagation of electron spin density polarization and spin currents in n-doped semiconductors within the two-component drift-diffusion model in an applied electric field (E). The drift and diffusion contributions to the spin currents are examined, which shows how the spin current could be enhanced. We find that there is a crossover field (Ex), where the drift and diffusion contribute equally to the spin current in the downstream direction. This suggests a possible way to identify whether the process for a given E would be in the drift or diffusion regime. We derive the expression for Ex and show that the intrinsic spin diffusion length in a semiconductor can be calculated directly from Ex. The results will be useful in obtaining transport properties of the carriers’ spin in semiconductors. This investigation, however, highlights the need for further experiments to be conducted to measure Ex in semiconductors.

Multiquantum well spin polarized current oscillator

We analyze nonlinear electron spin dynamics of a n-doped DC voltage biased semiconductor II–VI multi-quantum well structure (MQWS) having one or more of its wells doped with Mn. Even if normal contacts have been attached to this nanostructure, spin polarized current can be obtained provided one well is doped with magnetic impurities. We have studied the conditions for the system to exhibit static electric field domains and stationary current or moving domains and time-dependent oscillatory current. There are self-sustained current oscillations (SSCO) for nanostructures with four or more QWs. Moreover, SSCO may appear or not depending on the spin splitting induced by both, the exchange interaction and the external magnetic field. We calculate the minimal doping density needed to have SSCO, which is crucial to design a device behaving as a spin-polarized current oscillator.