摘要:

In this paper we present results of two‐dimensional numerical simulations of low voltage, high voltage, and vertical amorphous silicon transistors. The model input consists of one realistic density of states spectrum for undoped amorphous silicon, and one self‐consistent set of model parameters for all devices. Our results are in good agreement with experimental data, and this good fit is based on a new model for the source and drain contacts. Our approach is to treat these contacts as consisting of a fixed resistance in series with a small potential barrier whose height is modulated by current flow. Finally we show that relatively small changes in the density of deep localized states significantly alter the simulated device characteristics.

ISSN:0021-8979    

DOI:10.1063/1.347028

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Photodiodes with thin (∼0.2 &mgr;m) InGaAs light absorbing layers placed inside much wider (∼2 &mgr;m)InP depletion regions were studied to understand the interaction of hole trapping at the InGaAs/InP heterojunction interface and carrier transit effects. In the three devices studied, the absorbing region was located (i) near then+side, (ii) in the center, and (iii) near thep+side of the depletion region. The optical impulse response of these devices consists of a short pulse and a long exponential tail with a bias‐dependent time constant. The relative charge in the fast and slow components could be measured and it was shown that the charge ratios correspond to the fraction of the depletion region transited before and after trapping. These studies show that electron trapping times are much shorter than hole trapping times, and that fast photodetection can occur even in the presence of a severe hole trapping problem if the distance between the trap and thep+side of the depletion region is much smaller than the total depletion width.

ISSN:0021-8979    

DOI:10.1063/1.347029

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We present a theory of absorptive electro‐optic spatial light modulators based on GaAs/AlGaAs multi‐quantum well structures using arbitrary potential well profiles. In particular, we consider three different quantum well profiles: square, parabolic, and asymmetric triangular. We calculate the transition energies, oscillator strengths and absorption co‐efficients of the lowest‐lying heavy‐ and light‐hole excitons as a function of well width and electric field using a variational approach assuming decoupled valence subbands. For illustrative purposes we select the photon energy of the monochromatic source to be modulated at 1572 meV and aluminum concentration in the barriers to be 0.3. For the sake of comparison among the various modulators with different quantum well profiles we assume that this photon energy coincides with the lowest‐heavy‐hole exciton transition in the absence of an electric field. We find that the required well widths are 75 A˚ for the square well, 174 A˚ for the parabolic well, and 676 A˚ for the asymmetric triangular well. At zero electric field the values of the exciton oscillator strengths in all three quantum well systems are comparable. However, superior performance in terms of higher contrast ratio is obtained in the case of modulators based on asymmetric triangular wells. For instance, in the case of a square well with excitonic linewidth of 3 meV, a field of approximately 50 kV/cm is required to achieve a 30% decrease in absorption. On the other hand, the field required to achieve the same change in absorption in a parabolic well is 35 kV/cm and in an asymmetric triangular well is −7 kV/cm. The contrast ratio at an electric field of −20 kV/cm is 6.7 for an asymmetric triangular well and 1.02 for a square well in a multi‐quantum well sample where the contacts are 2 &mgr;m apart.

ISSN:0021-8979    

DOI:10.1063/1.347030

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The pressure‐induced wavelength shift of a laser‐excited fluorescence in samarium‐doped yttrium aluminum garnet (Sm:YAG) was compared with that of ruby to 26 GPa at room temperature. Because the fluorescence wavelength for Sm:YAG has a negligible temperature dependence, it provides a better pressure scale for diamond anvil cell applications than ruby under high‐temperature conditions. However, the overall intensity of the Sm:YAG fluorescence is less than that for ruby. A Gaussian–Lorentzian profile was chosen to analyze the fluorescence spectra. The Sm:YAG fluorescence wavelength exhibits an approximately linear pressure dependence (3.07±0.45 A˚/GPa) only to 20 GPa at room temperature. A polynomial fit for all data to 26 GPa givesP(GPa)=−10 280(&lgr;/&lgr;0−1)2+2085(&lgr;/&lgr;0−1), with a rms misfit of 0.14 GPa.<squeeze>

ISSN:0021-8979    

DOI:10.1063/1.347031

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We propose a phenomenological method to extend isotropic nonequilibrium distribution functions in semiconductors into field‐induced anisotropic forms. We show that the distribution functions which we derive for the &Ggr; valley of GaAs compare favorably to more precise Monte Carlo simulations. A complete set of transport coefficients for the mancroscopic current continuity and energy flux equations is also derived. These transport coefficients should be helpful to study the range of applicability of various hydrodynamic models in ultrasmall devices.

ISSN:0021-8979    

DOI:10.1063/1.347032

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have examined epitaxial InSb films by Raman scattering for the first time. The films, 0.17–2.67 &mgr;m thick, were grown on (100) GaAs substrates by the new technique of metalorganic magnetron sputtering. We observe the first and second order longitudinal optical phonon peaks, the latter enhanced by outgoing resonance with theE1+&Dgr;1gap of InSb, and an upshift of this gap due to compressive biaxial stress. We also observe an anomalous dependence of stress on film thickness. The Raman data indicate good sample quality despite the large lattice mismatch between InSb and GaAs.

ISSN:0021-8979    

DOI:10.1063/1.347033

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Bragg reflectors based on (Ca,Sr)F2and (Ga,Al)As are studied. Modeling and fabrication of these structures by molecular‐beam epitaxy were performed. Quarter‐wave Bragg reflectors were found to present an excellent reflectance around the wavelength of interest, 870 nm, for only three periods of bilayers. However, the structures grown exhibited cracks after epitaxy due to thermal stress between both materials. To alleviate this problem, other reflector geometries were investigated consisting of deviations from the classical Bragg reflector. The new geometries enable one to reduce the absolute or relative fluoride thickness within the structure. The results obtained show that the use of adequate geometries allows one to overcome the stress problem, and good heteroepitaxial reflectors with a crack‐free surface morphology were obtained.

ISSN:0021-8979    

DOI:10.1063/1.347034

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

AlN intended for metal‐insulator‐semiconductor applications has been prepared by laser activated chemical vapor deposition from ammonia and trimethylaluminum precursors. The films are high‐density polycrystalline with ⟨100⟩ preferential orientation, and there is no evidence of the presence of Al2O3. A consistent band gap of 6.00±0.03 eV is obtained for film thickness in the range 0.3–1.2 &mgr;m. Conductivity is below 5×10−14&OHgr;−1cm−1at room temperature and is thermally activated with a range of excitation energies between 0.6 and 0.8 eV. The breakdown electric field is about 3×106V/cm, while the relative permittivity varies between 7.8 and 8.2 in the frequency range 100 Hz–13 MHz.

ISSN:0021-8979    

DOI:10.1063/1.347035

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The heat transfer in the arc cathode spot is treated and an analytical expression is obtained, connecting the power loss by thermal conductionLtto the velocity, the temperature and the radius of the spot and to the properties of the cathode material. The contribution ofLtto the power balance in the arc cathode region and its incidence on the spot existence diagram are examined in the case of Hg and Cu cathodes.

ISSN:0021-8979    

DOI:10.1063/1.347036

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Mode structure in strip‐loaded waveguides is studied using an eigenvalue method based on a two‐dimensional Fourier analysis. Modified guides where the loading strip is displaced above the core by an additional layer of cladding are considered as a general case. Lateral confinement is found to depend largely on the extent to which the field decays over the strip, and generally worsens as vertical confinement (in the direction perpendicular to the layers of the guide) improves. Conditions that degrade lateral confinement include a large difference in refractive index between core and cladding, a core wide relative to operating wavelength, and large separation between strip and core. Lateral confinement does not vary monotonically with vertical confinement, moreover, but instead may be maximized over a specific range of the guide’s refractive indices.

ISSN:0021-8979    

DOI:10.1063/1.347037

出版商:AIP    

年代:1990

数据来源: AIP