摘要:

The frequency (&ohgr;) response of the admittance(Y)of Czochralski (Cz) and Bridgman (Bg) grown semi-insulating materials have been investigated in the range 300–500 K. For both materials, this conductivity remains constant up to a frequency &ohgr; at which it becomes proportional to&ohgr;1. A minimum is observed in theY(&ohgr;)characteristics between these two regimes in Cz materials but not in Bridgman ones. It is suggested that the existence of this minimum is related to percolation induced by the presence of space-charge regions located around As precipitates and charged dislocations, which are present in Cz but not in Bg materials. The percolation invalidates the homogeneous conduction assumption made in analyzing the electrical properties of semi-insulating Cz materials. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365964

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effects of crystal defects near the surface on the position of surface Fermi level(EFS)are investigated using photoluminescence (PL) measurements and synchrotron radiation photoelectron spectroscopy (SRPES). For the lightly Si-doped GaAs(001) surface, PL measurements reveal that after heating to 500 °C a layer with lower PL peak intensities related to gallium vacancies than those of the bulk exists just under the thermal degraded layer. SRPES shows thatEFSmoves upward to 1.1–1.17 eV above the valence band maximum when this thermal degraded layer is removed by chemical etching and the excess arsenic on the surface, which is formed by rinsing the etched surface with deoxygenated and deionized water, is evaporated by heating in ultrahigh vacuum (UHV). After evaporation of excess arsenic on the surface by heating, the etching-depth dependence ofEFSfor a sample preheated in UHV correlated with the existence of this defect concentration layer. These results suggest that the position ofEFSfor the GaAs(001) surface is strongly influenced by crystal defects near the surface. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365965

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We investigate the excitonic optical properties in thin quantum boxes in the intermediate regime between the two-dimensional (2D) and zero-dimensional (0D) with a theoretical analysis that rigorously treats excitonic confinement effects. It is found that the exciton binding energy is substantially enhanced and that the oscillator strength concentrates to the lowest excitonic transition, even in a thin box whose lateral width is considerably (about five times) larger than the Bohr radius. Novel optical properties experimentally observed in semiconductor quantum disks, which are the intense photoluminescence spectrum and ultranarrow photoluminescence excitation spectrum, are explained well by the theoretical results. We also calculate exciton absorption in a thin box in which an electric field is applied in the lateral direction. The present theory can simulate how the electroabsorption evolves from the quantum confined Stark effect in the 0D to the quantum confined Franz–Keldysh effect in the 2D with an increase in the lateral size of the box. In the intermediate regime between 2D and 0D, a strong excitonic electric-field effect, distinct from the well-known electroabsorption effects at 0D and 2D, is found. These theoretical results demonstrate that even though the lateral confinement is weak, it considerably enhances the electron–hole Coulomb interaction and alters excitonic optical features markedly in the thin quantum box. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365966

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We study the influence of interface roughness and dopant disorder on the electronic and charging properties of a &dgr;-dopedAl1−xGaxAs/GaAsquantum-dot grid-gate device by computer simulation. The analysis is performed for a device unit cell atT=4.2 K by self-consistent adiabatic one-dimensional (1D) Schro¨dinger and 3D Poisson’s simulation, within the local density approximation. Random boundary conditions that accounts for cell-to-cell influence of disorder is considered as well. The random effect of interface roughness produces very short-ranged potential distortions over distances of the order of a monolayer, resulting in a maximum deviation of 20&percent; in the charging energy. Sensitivity analysis of the device to both random fluctuations in the number and positioning of the dopant ions shows that dopant number variations from device to device can result in fluctuations in the charging energy of as much as 50&percent; per dopant. Isolated acceptor point charges in the quantum well change the modes of electron confinement, giving rise to fluctuations in the charging energy of the order of 25&percent;. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365967

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A closed, quantum, double barrier, GaAs/AlGaAs heterostructure is made chaotic by adding a nonlinear potential term,&agr;⟨Q(t)⟩,to the time-dependent Schro¨dinger equation, and the dynamical behavior of an electron cloud moving in the heterostructure biased by a dc electric field is examined numerically. Using phase-space diagrams, power spectrums, and Lyapunov exponents, both qualitative and quantitative measures of the chaos in the system were taken. In general, for all values of &agr;, the nonlinearity parameter, the Lyapunov exponent, &lgr;, increases as the applied dc field, &bgr;, increases. However, for values of&agr;⩽1.376,we notice a sharp drop in &lgr; for the value of&bgr;=−9.2×107 V/mcorresponding to an average dc voltage of−.085 eVin the central well. This first order type transition to high values of &lgr; for&agr;>1.376corresponds to a similar increase in the mean charge trapped in the heterostructure and in the average nonlinear potential in the central well for that dc field. This behavior is attributed to the fact that for&agr;⩽1.376and&bgr;=−9.2×107 V/m,the field effects dominate, but for&agr;>1.376,the nonlinearity term dominates. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365968

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The electrical effects of reactive ion etching (RIE) ofp-InP byCH4:H2are investigated. By using optical deep-level transient spectroscopy, several deep-level defects could be detected. The main defect (E3) is found to be a donor with an energy level atEc−0.38 eV. From depth profiles of both the net acceptor concentration and this defect, it follows that after RIE, the E3 defects are passivated by hydrogen. Simultaneous passivation of both acceptors and donors onp-InP is reported. Subsequent rapid thermal annealing at increasing temperatures shows that the E3 defects are first depassivated and then annealed out. The change of the Schottky barrier height with the anneal temperature could be explained by Fermi-level pinning due to E3 and depinning either by its passivation for low enough temperatures or by its annealing out at higher temperatures. Some possibilities concerning the physical nature of E3 are discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365969

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A series of periodically Si &dgr;-doped InP samples with 5 and 10 periods varying from 92 to 278 Å has been investigated in terms of the transport and optical properties. A reduction in mobility with decreasing period was observed due to the increasing overlap of the electronic wavefunction with the various Si planes. A broad band emission was detected for the periodic structures at energies higher than the InP band gap. The cutoff energy for this band decreases with the period and this behavior can be described by ad−2/3decay. The results are discussed and compared with the ones for GaAs available in the literature. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365946

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The dynamics of the bistable and oscillatory behavior of a heterostructure hot electron diode is investigated both theoretically and experimentally. Monte Carlo simulations are performed accounting for the scattering to subsidiary conduction band valleys of GaAs and AlGaAs. S-shaped current-voltage characteristics and self-sustained current oscillations in an external cavity are obtained in good agreement between theory and experiment. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365970

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Current transport and instability mechanisms in thin film diodes with nonstoichiometric silicon nitride(a-SiNx:H)semiconducting layers have been investigated. In common with amorphous silicon thin film transistors the electrical characteristics of these diodes have been found to drift during use. We found that the initial current-voltage characteristics are related to the choice of interfacial treatments. This is explained by trapping of electrons at interface defect states and by tunneling of electrons into the conduction band via these states. We have also found a relationship between the initial characteristics of the diodes and the rate of drift due to electrical stressing. A threshold exists below whose drift is independent of the current-voltage characteristics and above which there is a strong dependence. This dependence of drift on current-voltage characteristic is consistent with field enhanced defect creation in thea-SiNx:Hlayer. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365971

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The electrical properties of a thin (350 Å) layer deposited on a molecular beam epitaxial grownSi0.89Ge0.11/Si(001)heterostructure and subsequently annealed atTa=550–800 °Cwere studied in a wide (80–325 K) temperature range. Annealing at 800 °C produces a single reaction product, the C54 phase ofTi(SiGe)2,while lower temperature anneals result in the coexistence of a few intermetallic compounds. It was found that while for annealing temperatures lower than 800 °C, the Fermi level is pinned with respect to the conduction band, annealing at 800 °C results in Fermi level partial pinning with respect to the valence band. The current flow in this case is controlled mainly by thermionic emission in the presence of interface states. Two kinds of traps were observed by deep level transient spectroscopy in the barrier region after the 800 °C annealing. Acceptor-like traps with an activation energy of ≈0.46–0.5 eV, a capture cross-section&sgr;a=1.3×10−12 cm2,and a densityDt≈3×1013 eV−1cm−2,which most likely originate from the strain relaxation in the SiGe epilayer, were found to be responsible for the partial Fermi level pinning at the interface. Electron traps with an activation energy of ≈0.17 eV and a capture cross-section&sgr;d=7.7×10−16 cm2were also identified and attributed to the SiGe epilayer; they are assumed to originate from a well-known vacancy-oxygen center. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365972

出版商:AIP    

年代:1997

数据来源: AIP