摘要:

Ag&sngbnd;GaAs Schottky‐barrier photodiodes have been fabricated and evaluated as detectors of uv radiation. The quantum efficiency of these detectors is a maximum near 3225 Å, and is much less in the visible and ir regions of the spectrum. The peak quantum efficiency and selectivity of the detector is determined by the thickness of the silver layer, which possesses a narrow transmission ``window'' for radiation near 3225 Å wavelength. The transmittance of silver films evaporated on 7059 glass and quartz substrates was measured and compared with calculations based on previously published optical constants. At the transmittance peak, the extinction coefficient for these silver films was measured to be 0.38. From these transmittance measurements, the fraction of the radiation, incident on the silver, which enters the GaAs of the photodetectors was calculated as a function of wavelength and silver‐film thickness. This quantity was compared with the measured quantum efficiency of the diodes. At the peak, the comparison indicated that 25–50% of the carriers created within the depletion region of the barrier do not contribute to the photocurrent. Measurements of the dependence of quantum efficiency on bias and energy of the absorbed radiation suggest that at the peak, a fraction of the carriers created within the depletion layer are energetic enough to pass over the Schottky barrier and not be collected as photocurrent.

ISSN:0021-8979    

DOI:10.1063/1.1657037

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

An experiment has been performed in order to determine the dominant ionic species in a cesium plasma in the Torr pressure range. The device consists of a planar thermionic converter with a small (25 &mgr; diam) hole in the collector. Ions that pass through the hole are accelerated by an ion gun and analyzed in a magnetic mass spectrometer. It is found that atomic cesium ions are the dominant species in both the ignited and unignited modes of operation of the discharge. The molecular cesium ions Cs2+and Cs3+were also detected in the ignited mode. In addition, measurements were made of the total ion and electron currents that pass through the collector hole. Here the hole acts as a probe of the plasma adjacent to the collector.

ISSN:0021-8979    

DOI:10.1063/1.1657038

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

A representative number of abrupt GaAs junctions, asymmetrically doped, have been studied to delineate quantitatively the properties of spectra (called shifting‐peak spectra) whose peak energy approximately equals the applied voltageV, and shifts in position and intensity withV. The free‐electron concentrationnon the more lightly doped side was varied from 3×1017cm−3to 8×1018cm−3, the voltage range was ∼1.0 to ∼1.5V, and the temperature was varied from 12° to 255°K. Because the active region width is 600 Å or less, and the spectral shape agrees in all details with Morgan's theory of photon‐assisted tunneling, these shifting‐peak spectra have been identified as radiative tunneling. It is shown here that no adjustable parameters are needed to calculate the experimental spectral shape when onlyT, V, andnare specified. This means that for any given temperature,nalone represents the influence of the junction on the spectral shape, while the independent parameter in terms of excitation is the voltage and not the current, as usually stated. The agreement between the calculated and experimental spectra includes the logarithmic slope of the low energy tail, and the difference betweenVand the energy of the peak‐emission intensityhvp:eV0=eV‐hvp. This agreement emphasizes the necessity of including the parabolic junction potential as obtained from Poisson's equation when calculating the tunneling‐hole and electron‐wave functions. The usual simplifying assumption of a linear potential is inadequate. To clarify previous observations of one or two types of shifting‐peak spectra, linear‐graded and abrupt‐asymmetrical junctions were made from adjacent wafers of the same crystal, and the resulting shifting‐peak spectra were compared. Only band‐to‐band radiative tunneling was observed for the abrupt junction, but for the linear‐graded junction two shifting‐peak spectra were observed. In the low excitation region for linear‐graded junctions, the shifting‐peak spectra may be described by band‐to‐impurity radiative tunneling that results in a narrow active‐region width, while at higher bias the emission becomes band‐to‐band radiative tunneling with a wider active region. These results demonstrate that shifting‐peak spectra previously attributed to band filling may be described in terms of photon‐assisted tunneling.

ISSN:0021-8979    

DOI:10.1063/1.1657039

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

For studies of cataphoresis in He&sngbnd;Ne mixtures, an analytic expression is derived for the functional dependence of the neon atoms in the axial direction. The analysis, which involves the continuity equation, considers the production and loss mechanisms of the Ne+ions. The present theory can be used to predict the degree of ionization of neon at a given pressure and current, when the appropriate rate coefficients are known. In addition, techniques for ion sampling from gaseous plasmas have been used in the present investigation. Measurements have been made in commercial helium‐gas samples having a quoted neon concentration ≤0.001% and in samples containing 0.05% neon. Studies were conducted over a pressure and current range of 7–30 Torr and 8–80 mA, respectively. Depending on the experimental conditions, the following ions were observed: He2+, Ne+, Ne2+, and HeNe+. For the case of HeNe+, the present studies permit an estimate of the rate coefficient for the reaction Ne++2He→HeNe++He which is comparable to values obtained from afterglow studies. Measured values of the degree of ionization are in good agreement with values calculated using the present theory.

ISSN:0021-8979    

DOI:10.1063/1.1657040

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The measurement of the erosion at the electrodes of an arc rotated between water‐cooled nonrefractory coaxial electrodes in an axial magnetic field has been made in air at atmospheric pressure. Values of erosion rate an order‐of‐magnitude less than those previously reported have been obtained. The effect of variation in axial magnetic flux density, arc velocity, rotational frequency, cooling‐water flow‐rate, and electrode wall thickness have been investigated. A steady‐state model, taking into account the nonuniform thermal distribution in the electrode below the arc root, has been obtained in terms of the electrode dimensions normalized with respect to the diameter of the arc root. The minimum conditions for the surface of a cold‐cathode electrode to be maintained below the melting point of the electrode material are deduced.

ISSN:0021-8979    

DOI:10.1063/1.1657041

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The interaction of Li atoms with O impurities and with defects produced in Si by 1.5 MeV and 47 MeV electrons was studied using infrared spectroscopy. Li was diffused in low oxygen‐containing uncompensated Si with initial resistivity in the range 15–28 500 &OHgr;·cm and in high oxygen‐containing Si with initial resistivity of 15–200 &OHgr;·cm. The Li concentration in the samples varied from about 1016to ≲1019Li atoms/cm3. New radiation‐induced bands at 1.4 and 1.7 &mgr; are observed. Divacancy production as measured by the 1.8 and 3.3 &mgr; defect bands is markedly decreased in samples of high Li content with concomitant growth of the Li‐associated 1.4 and 1.7 &mgr; bands. Annealing of the 1.4 and 1.7 &mgr; bands strongly depends upon the Li concentration. Recovery occurs at a temperature of 150°C for the 1.4 &mgr; band, and at 350°C for the 1.7 &mgr; band, for samples containing ∼6×1017Li/cm3. In samples containing ∼2×1016Li/cm3, the bands at 1.4 and 1.7 &mgr; disappear after annealing at 330° and 470°C, respectively. Sharp Li‐ and O‐associated defect bands in the 700–1000 cm−1range are produced only in high O‐containing samples, and the presence of Li has a pronounced effect on the production and recovery of theA‐center defect (830 cm−1band). In samples of high Li content, the predominant absorption is due to free carriers and is found to be in agreement with predictions of theory. A search for defect absorption bands attributable to vibrational modes of the isolated interstitial Li+ions yielded negative results.

ISSN:0021-8979    

DOI:10.1063/1.1657042

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Electronic conduction in thermally grown SiO2has been shown to be limited by Fowler‐Nordheim emission, i.e., tunneling of electrons from the vicinity of the electrode Fermi level through the forbidden energy gap into the conduction band of the oxide. Fowler‐Nordheim characteristics have been observed over more than five decades of current for emission from Si, Al, and Mg. If previously measured values of the barrier heights are used, the slopes of the Fowler‐Nordheim characteristics (logJ/E2vs 1/E) imply values of the relative effective mass in the forbidden band of about 0.4. These values take into account corrections for image‐force barrier lowering and for temperature effects. The absolute values of the currents are lower by a factor of five to ten than the theoretically expected values, probably due to trapping effects. The temperature dependence of the current was found to follow the theoretical curve from 80°–420°K. However, an inconsistent relative effective mass of about 0.95 had to be assumed. These results are believed to provide the most complete examination of the Fowler‐Nordheim‐emission theory.

ISSN:0021-8979    

DOI:10.1063/1.1657043

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The change in work function of the (100) surface of a tungsten single crystal was measured as a function of time as gas adsorbed on the surface. Using a simple model, the work function changes for monolayer coverage were found to be 0.94 eV, −0.7 eV, 0.21 eV, and 0.44 eV, for O2, N2, H2, and CO2, respectively. The initial bare surface sticking probabilities were found to be 0.24, 0.37, 0.63, and 0.29, respectively. The initial changes in work function per molecule were found to be 9.4×10−16eV, −7×10−16eV, 2.1×10−16eV, and 1.75×10−15eV, respectively.

ISSN:0021-8979    

DOI:10.1063/1.1657044

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Strong electric fields have been applied to dielectric polymer films to study field‐induced mechanical stresses. For voltages near breakdown the mechanical forces are sufficient to cause localized deformation in some polymer films. Considerable field enhancement can occur at the deformation sites, leading to reduced nominal dielectric strength for the samples. Experimental evidence for electromechanical deformation is presented as a possible explanation for the poor agreement between the observed dielectric strength and that predicted theoretically.

ISSN:0021-8979    

DOI:10.1063/1.1657045

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

When polychromatic radiation is used in x‐ray diffraction, the instrumental broadening changes with the scattering angle. It is shown that when transmission geometry is used, the instrumental broadening can be expressed in terms of the profile of the primary beam and its wavelength distribution. Consequently, it becomes possible to correct the entire intensity profile for instrumental broadening. The correction is made by successive foldings of the observed profile, and is demonstrated using the intensity profiles of raw and heat‐treated carbon black.

ISSN:0021-8979    

DOI:10.1063/1.1657046

出版商:AIP    

年代:1969

数据来源: AIP