摘要:

Interactions in the Co/Si thin‐film system were investigated by MeV backscattering and x‐ray‐diffraction techniques. It was found that Si diffuses through the Co layer and accumulates at the sample surface at about 300 °C. Increasing the temperature causes the growth of the Co2Si phase, followed by the simultaneous growth of the CoSi phase. The growth rates for both phases have a square root of time dependence. The activation energies of growth are 1.5 and 1.9 eV for the Co2Si and CoSi phase, respectively. A model for the growth of multiple phases is suggested. The transformation between CoSi2and CoSi is found to be a reversible reaction.

ISSN:0021-8979    

DOI:10.1063/1.325359

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The Kirkendall effect in thin‐film Co/Si couples is investigated by He backscattering using diffusion markers. The couples contain the compounds Co2Si and CoSi. The markers used are Xe implanted into Si, C, or Co2Si and a discontinuous W film between Si and Co. In the case of Xe implantation into Co, the experiments can be explained by dragging of Xe bubbles by the moving Co/Co2Si phase boundary. Xe implanted into Si is located at the Si/CoSi interface after the reaction and W is found at the Co/Co2Si interface after the reaction. The same applies to Xe implanted through Co into Co2Si. The results are evidence for predominant Co diffusion in Co2Si growth and Si diffusion in CoSi growth. Grain‐size measurements suggest that grain‐boundary diffusion plays a role in the growth of the silicide layers. The results of a Xe implantation into Co2Si without Co suggests that at the Co2Si/CoSi interface both Si and Co diffusion currents flow.

ISSN:0021-8979    

DOI:10.1063/1.325360

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

On the basis of thermochemical equilibria considering interactions between dopants and vacancies, the carrier concentration, electron mobility, minority‐carrier lifetime, and luminescence intensity, which have been measured as a function of the Ge concentration in a solid, are analyzed for Ge‐doped vapor‐grown GaAs. The quadratic dependence of the carrier concentration on dopant partial pressure is observed in Ge‐ and Sn‐doped GaAs and is reasonably explained by the hypothesis that the dominant donor is the diatomic complex formed between Ge or Sn substitutionals incorporated in the nearest‐neighbor Ga sites. For Ge‐doped GaAs, considering that the diatomic Ge donor and monoatomic Ge acceptor are dominant charged species in the extrinsic doping range, the measured electrical and optical properties are uncontradictorily explained with quantitative agreement. Using this double‐donor–double‐acceptor model, the origin of the space charges which significantly decrease electron mobility and the origin of minority‐carrier killer centers which cause concentration quenching of luminescence in the extrinsic doping range are speculated to beVGa‐GeAscomplexes andVGa‐ (GeGa)2complexes, respectively. The self‐compensation ratio of Ge,N−A/N+D, reduces to the minimum value (∼0.1) near the boundary between the intrinsic and the extrinsic regions.

ISSN:0021-8979    

DOI:10.1063/1.325361

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A mathematical analysis of the expected short‐circuit current density in Schottky‐barrier solar cells is presented. For a solar cell with the Schottky barrier on the bottom, back illuminated, the active semiconductor material, GaAs for this example, must be a thin film for maximum efficiency. A comparison between this cell and a single‐crystal solar cell with the Schottky barrier on the top, front illuminated is made. This comparison shows that solar cells made from polycrystalline films could deliver the same short‐circuit current as a single‐crystal solar cell provided that the minority‐carrier diffusion length in the polycrystalline films can be kept to within one order of magnitude lower than that for the single‐crystal material. The reason for this is that solar‐reflection losses for the back‐illuminated thin‐film cell can be minimized, while for the front‐illuminated single‐crystal cell the losses must always be high.

ISSN:0021-8979    

DOI:10.1063/1.325362

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The photogeneration of holes in poly(N‐vinylcarbazole) has been investigated as a function of applied electric field, wavelength, and temperature. For fields above 3.0×104V/cm, the field and temperature dependences of the photogeneration efficiency are in good agreement with predictions based on the Onsager theory of geminate recombination. The quantum efficiency can be described by a thermalization distance which varies from 26 to 30 A˚ as a function of wavelength and a primary quantum yield which varies between 0.20 and 0.03 as a function of temperature. The photogeneration efficiency increases in steps with decreasing wavelength. Transitions occur between the ground state and the first, second, and third excited singlet states. For a given transition, the efficiency is constant and depends only upon the electric field and temperature. The increase in efficiency which occurs with decreasing wavelength can be explained by an increase in the thermalization distance. The primary quantum yield shows an exponential dependence on reciprocal temperature with an activation energy of 0.05 eV. The thermalization distance is independent of temperature and determined only by the excitation wavelength.

ISSN:0021-8979    

DOI:10.1063/1.325363

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A comprehensive model for minority‐carrier transport due to a quasi‐electric‐field in graded‐composition semiconductor materials is developed including effects due to nondegenerate high‐level injection of excess electrons and holes. For low‐level injection, equivalent to a one‐sun photoexcitation of uniformly doped direct‐ or indirect‐band‐gap material the total quasifield is given by the standard gradient of band‐gap energy. High‐level injection asymptotically reduces quasifield components due to band‐gap and effective‐mass gradients to lower values, and essentially eliminates components due to equilibrium‐ and excess‐carrier concentration gradients. The impact of these results on performance ofp‐n‐pandn‐p‐ngraded‐band‐gap base transistors operated at high currents is examined.

ISSN:0021-8979    

DOI:10.1063/1.325364

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

By means of novel differential techniques, we have studied the writing and erasing dynamics of DDC cells and, in the process, uncovered a number of unexpected phenomena which play an important role in these processes. For example, we find writing currents qualitatively similar to, but considerably in excess of, those predicted earlier by Fowler‐Nordheim studies on similar MOS structures. We find that these devices can be written with high and undiminished efficiency to 7–10 V of flatband shift depending on insulator thickness, and we determine the limiting source of efficiency degradation beyond these levels. In erase, we find an interesting enhancement due, we believe, to electron‐electron repulsion of the net stored charge. By studying the reversible motion of the stored‐charge centroid at high temperatures, we determine that the effect of the interfacial dopant on the outer insulator extends about 80 A˚ into this layer. Other studies indicate an effect on the thin oxide to be less than 20 A˚. Low‐field long‐time charging results point to a Fowler‐Nordheim–like writing current versus oxide field extending at least from 4.2 to 10 MV/cm, a range of no less than 109in current density for oxide thicknesses of 80 A˚ or more. All these features and others were found and investigated using quite standard flatband measurements, albeit, by the use of novel patterns of writing and erasing.

ISSN:0021-8979    

DOI:10.1063/1.325365

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The transient velocity characteristics of electrons in GaAs have been calculated for uniform electric fields at room temperature. Three‐level band‐structure data have been used with a Monte Carlo simulation program to predict electron drift velocity, temperature, and valley population fractions as functions of position and electric field. Results for two three‐level band‐structure models are compared with those for the previously accepted two‐level model. Transient and steady‐state properties are seen to be sensitive to some material parameters whose values are still in dispute.

ISSN:0021-8979    

DOI:10.1063/1.325366

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A symmetrical‐Schottky‐barrier (SSB) band model is proposed for the carrier transport in oxygen‐rich polycrystalline‐silicon films. Semiquantitative analyses were made, comparing a one‐dimensional depletion approximation, with voltage and temperature‐dependent current measurements. The band gap is found to be similar to that of single‐crystalline Si, with electrons as the majority carriers. A net donor state density of 2.3×1019cm−3, 0.12 eV below the conduction band edge, exists in the grains of the polycrystalline silicon, and these donors are completely ionized in the presence of large grain‐boundary surface states. This results in a grain‐boundary surface‐charge density of −2.3×1013q/cm2, setting up overlapped space‐charge regions which give rise to the SSB band structure with a maximum band bending of 0.44 eV. The Fermi level is found to be pinned at the midgap at the grain boundaries—suggesting the existence of an amorphous intergrain layer. At and above 373 K, the carrier transport is by thermionic emission, TE. Below 373 K, it is dominated increasingly by a tunneling process, i.e., thermionic field emission, TFE. The current increases with applied voltage according to a sinh function. A calculated effective Richardson constantA** of ∼70 A cm−2 K−2and a lower quantum‐mechanical reflection, but higher electron‐optical phonon backscattering than those of a metal‐Si Schottky barrier, are found in the TE regime. The grain size deduced from the model agrees with that measured with a TEM: 100±41 A˚. The band picture also agrees with the photoelectric threshold measurement.

ISSN:0021-8979    

DOI:10.1063/1.325367

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Electron trapping in the SiO2layer ofn‐channel polycrystalline silicon‐SiO2‐silicon field‐effect transistors with electron‐beam‐evaporated aluminum was studied. The increased electron trapping was attributed to the x rays generated when the electron beam impinged on the aluminum target. Traps with low‐field capture cross sections greater than 10−13cm2are associated with the x‐ray‐induced positively charged centers, while traps with low‐field capture cross sections of about 1×10−15cm2are associated with the x‐ray‐induced neutral centers. For the silicon‐gate devices, both traps could be effectively reduced by annealing in dry forming gas at 550 °C for 20 min. As reported earlier, the capture cross section of the positively charged traps has a strong field dependence of approximatelyE−3oxand is approximately independent of temperature. The field dependence of the capture cross section of the neutral traps is much weaker, with roughly a &sgr;  =&sgr;0 exp(−bEox) dependence, where &sgr;0=1.6×10−15cm2andb=7.35×10−7cm/V. A possible origin of these neutral traps is displaced bonds forming polarization potential wells.

ISSN:0021-8979    

DOI:10.1063/1.325368

出版商:AIP    

年代:1978

数据来源: AIP