摘要:

Films of hydrogenated amorphous silicon carbide (a‐SiC:H) have been prepared by a glow discharge decomposition from gas mixtures of C3H8‐SiH4‐H2and CH4‐SiH4‐H2, in order to examine the effect of hydrocarbon gases on the structural and optical properties of these films. To study the influence of hydrogen on those properties of the propane‐based films, the properties of the films deposited at different substrate temperatures (Ts) are systematically investigated using infrared (IR) and ultraviolet‐visible absorption spectroscopies. By observing the change of intensities of IR absorption peaks with substrate temperature, the hydrogen bonding responsible for the absorption peaks could be assigned more accurately. WhenTsis increased up to 300 °C, intensities of CH3and SiH2groups are reduced, indicating the formation of a dense network structure. At the same carbon concentration in gas mixtures, propane allows more carbon and hydrogen atoms to be effectively incorporated into the film than methane. The IR spectra reveal that the structure of a propane‐based film has the characteristics of that of two kinds of films, methane‐ and ethylene‐based films. It is found that the chemical bonding nature of the hydrocarbon gas strongly affects the bonding structure and the composition of the films. From these results, it is proposed that the use of propane is suitable for the fabrication of high‐qualitya‐SiC:H with a wide optical gap (≳2.0 eV) and a deposition rate of ∼2 A˚/s.

ISSN:0021-8979    

DOI:10.1063/1.352007

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The absorption spectrum of Ho3+ions in yttrium scandium gallium garnet (Ho3+:YSGG) is reported at 4 K between 1.93 and 0.28 &mgr;m. Laser excitation spectra and laser‐excited fluorescence spectra from Ho3+(4f10)2S+1LJmultiplet manifolds5F4,5S2, and5F3to the ground‐state manifold5I8were obtained at 4, 8, and 70 K. Unresolved emission is observed from Ho3+ions in slightly disturbed cation (Y3+) sites along with emission coming from Ho3+ions occupying the regular cation (Y3+) sites having D2symmetry. Temperature‐dependent transitions (hot bands) observed in absorption at 8 and 70 K establish experimental crystal‐field split (Stark) levels in 24 excited manifolds and the seven lowest energy Stark levels in5I8(Z1=0,Z2=6,Z3=17,Z4=29,Z5=87,Z6=95, andZ7=102, all in cm−1). An algorithm is used to establish D2symmetry labels &Ggr;1, &Ggr;2, &Ggr;3, or &Ggr;4of individual experimental Stark levels. These levels are compared with results obtained from a calculation in which a parameterized Hamiltonian was diagonalized within the 50 lowest multiplet manifolds of Ho3+(4f10). Comparison between 157 experimental Stark levels and the corresponding predicted levels out of a total of 486 calculated levels yields a root‐mean‐square deviation of 5 cm−1.

ISSN:0021-8979    

DOI:10.1063/1.352008

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A recently developed theory of steady‐state conduction of space charge limited (SCL) currents in polyethylene doped with carbonyl hopping sites, and including detrapping, is modified to apply to the injection limited case, i.e., to a nonzero fieldF0at the injecting electrode. Good agreement with experiment was previously obtained for SCL carriers (F0=0) for applied fields up to 0.33 MV/cm. Here, we assume that for higher fields,F0is proportional to the difference between the applied field and 0.33 MV/cm. Excellent agreement between theory and experimental current‐applied field characteristics is then obtained for fields up to 0.5 MV/cm. The field distributions in doped and ‘‘pure’’ polyethylene samples are calculated, and are found to be independent of temperature in the range 49–82 °C for constant field.

ISSN:0021-8979    

DOI:10.1063/1.352009

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The dependence of the photoconductive gain on the photocarrier injection mechanisms from the surface and the substrate is investigated in GaAs photoconductive detectors. The layer structure and its effect on the dependence of the static gain on both the illumination intensity and the temperature is reported. The effect of deep traps on the gain response to illumination modulation intensity and the generation‐recombination noise is modeled.

ISSN:0021-8979    

DOI:10.1063/1.352010

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Ensemble Monte Carlo calculations of the steady‐state electron drift velocity in degenerate bulk GaAs using a self‐consistent algorithm specially tailored to directly include the electron‐plasmon interaction are presented. The critical issues implicit in the direct approach are the mesh size, charge assignment to the mesh nodes, interpolation of the field at the particle location, and the frequency with which the solution of the Poisson equation is updated. All of these factors determine the stability of the system, the accuracy, and the computational time required in the calculation. Comparison is made to quantum mechanically based techniques in which the electron‐plasmon interaction is treated as an additional scattering mechanism. It is found that the steady‐state electron drift velocity in bulk degenerate GaAs calculated using the semi‐classical approach for the electron‐plasmon interaction is significantly less than that calculated assuming no electron‐plasmon interaction is present. The steady‐state drift velocity calculated using the quantum mechanical approach, wherein the electron‐plasmon interaction is treated as a separate scattering mechanism, is affected in the opposite way, i.e., the velocity is greater than in the absence of the electron‐plasmon interaction. Neither model can at present be considered complete and caution should be exercised in adopting either approach in device simulation until a more satisfactory model has been developed.

ISSN:0021-8979    

DOI:10.1063/1.352011

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Hole mobilities of 1,1,‐bis(di‐4‐tolylaminophenyl)cyclohexane (TAPC) doped bisphenol‐A‐ polycarbonate have been measured over a range of concentrations. The mobilities are strongly concentration dependent, increasing with increasing TAPC concentration. The results are described within the framework of the disorder formalism, due to Ba¨ssler and co‐workers. The formalism is based on the assumption that charge propagation occurs by hopping through a manifold of states subject to concurrent energetic and positional disorder. The results show that both energetic and positional disorder increase with decreasing TAPC concentration. The increase in energy disorder is attributed to dipole moments of the carbonyl groups associated with the polycarbonate while the increase in positional disorder is suggested as due to packing constraints induced by the polymer host.

ISSN:0021-8979    

DOI:10.1063/1.352012

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Indium tin oxide (ITO)/silicon oxide/silicon (Si) junction solar cells were produced by depositing ITO on a thin silicon oxide‐covered single‐crystal Si substrate using the electron‐beam evaporation method. The current‐voltage (I‐V) characteristics strongly depended on the incident angle (&thgr;i) of the evaporated ITO vapor to the Si substrate during the ITO deposition, as well as the post‐deposition heating temperature (Th) and the kind of the ambient gases during post‐deposition heat treatment. The ITO films deposited at &thgr;i=0° and treated atTh=380 °C in air formed a high‐energy barrier withp‐Si, and formed ohmic contact withn‐Si. X‐ray diffraction analysis showed that the ITO films deposited at &thgr;i=0° contained metal indium. The amount of the metal indium decreased either by reducing the deposition rate of the ITO film or by raising the substrate temperature during the ITO deposition. The ITO films deposited at &thgr;i=45° and treated atTh=350∼450 °C in hydrogen, on the other hand, formed a high‐energy barrier withnSi. In this case, no metal indium was observed in the ITO films. It is concluded that the formation of the metal indium in the ITO films changes their work functions, and thus its presence strongly affects theI‐Vcharacteristics of the ITO/silicon oxide/Si solar cells. Darkening observed for the ITO films deposited at &thgr;i=0° is also attributed to the presence of the metal indium.

ISSN:0021-8979    

DOI:10.1063/1.352013

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The effect of electron‐hole scattering on transport in semiconductors has been considered from first principles. We conclude that the conventional equations for electron and hole currents are theoretically incorrect when electron‐hole scattering is present. From thermodynamic considerations, we introduce the more general equations. A Boltzmann transport calculation including electron‐hole scattering has been performed for Si. The key result is that the impact of electron‐hole scattering depends primarily on the relative velocities of electrons and holes and therefore shows up differently in different device situations. Electron‐hole scattering has the largest effect during conduction in high‐level injection. This is because electrons and holes have net drift velocities in opposite directions. In contrast, electron‐hole collisions have almost no effect on ambipolar diffusion because the carriers are moving in the same direction. Intermediate cases are also covered by this treatment. In low injection, electron‐hole scattering serves to reduce the effective minority‐carrier mobility. The degree of the reduction depends on whether the majority carriers are nearly static, as in diffusion situations, or whether they are flowing by drift, as in the Haynes–Shockley experiment.

ISSN:0021-8979    

DOI:10.1063/1.352014

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The den Boer analysis of single carrier space charge limited currents is commonly used to determine the density of states function within the gap of amorphous silicon hydride and other newly emerging materials. By using a device simulator, we assess the validity and accuracy of this analysis. In particular, den Boer’s assumptions of 0 K occupation statistics, a spatially uniform distribution of injected charge carriers, spatially uniform material, no generation/recombination, and no contact effects are investigated. We find that in the absence of contact effects and with spatially uniform states the den Boer analysis is accurate to within a factor of 2. However, current limiting due to contact effects at higher current values and diffusion dominated current at lower applied biases should not be mistaken for features of the density of states. In addition, if the gap states are not spatially uniform, gross overestimates (by as much as an order of magnitude for the device studied here) of the density of states can result. In general, only a limited range of the gap of the semiconductor can be mapped with this technique for a single device length, although multiple device lengths can be used to increase this range.

ISSN:0021-8979    

DOI:10.1063/1.352015

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

In this article we report the first detailed study of electrochemical capacitance‐voltage profiling of ZnSe. An electrolyte consisting of 1 M sodium hydroxide and 1 M sodium sulphite has been developed that does not deposit selenium while etching the surface ofn‐type ZnSe duringC‐Vprofiling. The dissolution number of the electrolyte/ZnSe system is a function of the strength of electrolyte and the etching current and in order to obtain an accurate etching depth a constant etching current mode was used. A wide range of doping concentrations including both uniformly doped and staircase structures have been measured demonstrating that the electrochemicalC‐Vprofiler can now be a routine tool for assessing the growth parameters of ZnSe.

ISSN:0021-8979    

DOI:10.1063/1.352016

出版商:AIP    

年代:1992

数据来源: AIP