摘要:

ZnS crystals were grown by sublimation in the presence of either H2S (``group S'') or a mixture of Ar and HCl (``group Cl''). Electroabsorption and polar rectification measurements indicate that permanent, high internal electrical fields exist in crystals of both groups. The anomalous photovoltaic effect (APE) is, however, observed only in the crystals of group S. For both groups, the sign of carriers excited by ir illumination was established by point‐contact rectification. The Fermi level in the dark, in group S crystals, was found to be within 0.9 eV of the valence band, while in group Cl it lies in the upper half of the forbidden gap. These measurements, along with photoluminescence results indicate that the free‐electron lifetime is considerably longer in group Cl crystals than in group S crystals. This difference in lifetime furnishes a simple explanation for the absence of the APE in crystals of group Cl.

ISSN:0021-8979    

DOI:10.1063/1.1658566

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A multiple‐pass Mach‐Zehnder laser‐illuminated interferometer has been constructed and used to measure the electron density profile of plasmas produced by a self‐confined propagating electron beam. Spatial and time resolved data were taken perpendicular to the electron beam axis at two longitudinal positions. Densities of 1016cm−3have been seen in air between 0.15 and 0.3 Torr as early as 150 nsec after the electron beam entrance. Peak densities of 1017cm−3were typically reached at around 2 &mgr;sec. Plasma compression was observed under some conditions.

ISSN:0021-8979    

DOI:10.1063/1.1658567

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

This paper deals with cylindrical cavity resonators containing weakly ionized gases, principally argon, in the pressure range of 0.03–0.70 Torr. The plasma, produced either by microwave or dc power, is magnetized by a uniform axial field. Measurements of resonant frequency, made over a range of plasma densities and magnetic field, are compared with the calculations of the theory given by Kent [J. Appl. Phys. 39, 5919 (1968)]. The agreement is good providing the cylindrical degeneracy of the cavity is preserved and the plasma is reasonably uniform. Experimental and analytical results are used to evaluate perturbation theory, and some simple formulas, useful for diagonostic purposes, are given. A perturbation method for correcting the theory to account for symmetrical nonuniformities is proposed, and it is applied to the experimental data with apparent success. The method offers the possibility of determining both uniformity and density from measurements of frequency in one microwave band.

ISSN:0021-8979    

DOI:10.1063/1.1658568

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Low‐energy Ar+sputtering yields have been obtained for solid and liquid tin from threshold to 1200 eV. The solid yield at 200 eV is twice that for the liquid but a crossover occurs at 375 eV above which liquid yields are 15% higher. The liquid‐yield curve exhibits a linear dependence up toE=475 eV and breaks sharply to a lower dependence on ion energy. Yields of remelted solid were intermediate between the curves for liquid and solid, demonstrating the effect of surface roughness on the yield for polycrystalline targets. This work confirms experimentally the theory of Sigmund for yield of amorphous targets particularly in the low‐energy range near threshold where surface effects predominate.

ISSN:0021-8979    

DOI:10.1063/1.1658569

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Radio‐frequency sputtering has been used to deposit films of intermetallic binary systems (AxBy) in which the composition varies continuously from about 10 at.% to 80 at.% for theBconstituent. Within this composition range the following &bgr;‐tungsten structured compounds were obtained: V3Si, Nb3Sn, Nb3Pt, Nb3Au, Nb3Al, Nb3Ge, and Ta3Ge. For films with thickness ranging from 3000 to 10 000 Å values ofTcwere observed which were within 1°K of previously reported best bulk values. In the case of Ta3Ge a new &bgr;‐W superconductor has been found with aTcof about 8°K.

ISSN:0021-8979    

DOI:10.1063/1.1658570

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The effect of hydrostatic pressure up to 10 000 kg/cm2on excess carrier lifetime in single‐crystal samples ofn‐ andp‐type germanium has been studied over a temperature range of 200°–350°K. The results of the experiments are interpreted in terms of existing theories of charge carrier recombination via recombination centers, and expressions for the variation of recombination level energies within the forbidden energy gap as a function of pressure are inferred. These variations are understandable on the basis of a simple Bohr model of defect levels in a dielectric medium whose dielectric constant varies with pressure. Tentative suggestions relating the recombination centers in the experimentally investigated samples to the presence of interstitial and substitutional impurity atoms are advanced.

ISSN:0021-8979    

DOI:10.1063/1.1658571

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Experiments are reported demonstrating the importance of contact characteristics for the high‐field (average field≳ionization field) microwave emission from InSb. Large voltage drops across the contacts are associated with low threshold currents for the onset of microwave emission. Thermal overloading the contacted sample by high pulse currents results in both a drop in overall resistance and a rise in threshold current and threshold magnetic field. Cessation of microwave emission after a thermal overload may be due to an annealing process in the contact region and is not necessarily connected with any damage to the crystal structure.

ISSN:0021-8979    

DOI:10.1063/1.1658572

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Time‐decay measurements of the photoexcited red luminescence near room temperature in a series of GaP (Zn, O) samples with varying zinc concentrations and varying thermal histories (annealing conditions) are presented. A phenomenological analysis of the electron recombination processes in GaP (Zn, O) based on semiconductor statistics and a simple kinetic model is then discussed which takes the (accurately measurable) time decays as independent variables and predicts the values of less accurately known quantities. It is demonstrated that such elusive but important parameters as the internal quantum efficiency, and the relative strengths of radiative and nonradiative centers, can be quantitatively predicted using time‐decay and free‐hole‐concentration measurements. Curves of internal quantum efficiency are presented as functions of the experimentally measurable time decays and free‐hole concentrations; as is the ratio of the capture time of the nonradiative centers to the capture time of the Zn&sngbnd;O complexes. These curves lead to an explanation of the dependence of the luminescent time decay of a sample on its previous thermal history. The explanation depends on (1) thermalization of electrons captured by Zn&sngbnd;O complexes back into the conduction band, (2) the presence of nonradiative recombination centers, and (3) a change in the relative concentrations of radiative and nonradiative recombination centers with annealing. From an analysis of the luminescent time decays it is predicted that the energy level of an electron on a Zn&sngbnd;O complex is 0.24±0.02 eV below the conduction‐band edge at room temperature. The temperature dependences of the luminescent decay and the external quantum efficiency (measured in the range 300°–450°K using both above and below bandgap photoexcitation) can also be understood on the basis of the model. When the intrinsic radiative excitonic lifetime is allowed to vary as a function of exciton binding‐energy agreement between predicted and measured photoluminescent quantum efficiencies results.

ISSN:0021-8979    

DOI:10.1063/1.1658573

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Methods for determining the mobility‐lifetime (&mgr;&tgr;) product of high‐resistivityn‐ orp‐type semiconductors using induced conductivity resulting from high‐energy beta and gamma irradiations are developed. The &mgr;&tgr; product is determined, under conditions of steady‐state excitation, from the measured induced conductivity and the calculated electron‐hole generation rateg. The carrier free lifetime &tgr; is determined from these results using the measured Hall mobility. For gamma irradiationgis determined from the exposure rate, density, mass energy‐absorption coefficients, and radiation‐ionization energy (&egr;). For beta irradiationg&bgr;is determined for the case of ionization resulting from the beta decay of radioisotopes which are produced by neutron irradiation and which are randomly distributed throughout the semiconductor.g&bgr;is determined from the radioactive decay rate, energy of the beta radiation, and &egr;. The absorbed dose rates resulting from these radiations are also determined. Gamma‐induced conductivity experiments were performed using60Co gamma irradiation on high‐resistivityn‐type CdS, CdSe, GaAs, and ZnS single crystals. The measured &mgr;&tgr; products ranged from ∼10−5to 25 cm2/V; &tgr; varied from ∼10−8to 10−1sec. Some reduction in &mgr;&tgr; resulting from high‐temperature annealing of CdS and GaAs was also observed. Beta‐ and gamma‐induced conductivity experiments (32P beta decay and60Co gamma irradiation) were performed on neutron‐irradiated CdS single crystals. Comparison of these results show that: (1) The &mgr;&tgr; products determined at a given dose rate from the beta and gamma irradiations are in very good agreement (within 15%). Thus, the theories developed here for determininggandg&bgr;are valid. (2) For samples which have considerable neutron damage, &mgr;&tgr; is very dependent upon exposure rate (or absorbed dose rate); decreasing with increasing exposure rate. This is in contrast to samples which have minimal (or no) neutron damage, where very little dependence on exposure rate is observed. (3) The &mgr;&tgr; product is also dependent upon the conductivity or Fermi level position. For irradiated high‐resistivity crystals &mgr;&tgr; is 1–6 cm2/V, and &tgr; is of the order of tens of msec. However, for irradiated low‐resistivity crystals &mgr;&tgr; is larger by a factor of ∼102, and &tgr; is of the order of seconds. The dependence of &mgr;&tgr; on the excitation intensity, defect concentration, and Fermi level position in neutron‐damaged samples results from sensitizing centers associated with neutron‐induced defects. The concepts developed here have resulted in new techniques for measuring neutron fluences using electrical changes associated with induced radioactivity in semiconductors. Gamma‐induced conductivity provides a valuable technique for ``calibrating'' these detectors (i.e., determining the &mgr;&tgr; product).

ISSN:0021-8979    

DOI:10.1063/1.1658574

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Green and blue photoluminescence has been observed below 100°K in vacuum‐deposited low‐resistivity CdS films given no post‐deposition treatment. The films were deposited on fused quartz substrates in a heated chamber inside the bell jar on substrates held at temperatures between 140° and 180°C. The CdS evaporant containing a trace of residual chlorine gave polycrystalline films that had resistivities at 300°K in the range of 1–102&OHgr; cm parallel to the substrate. The green luminescence in the films at 77°K was similar to the emission reported in the literature for donor‐doped CdS. The doped‐CdS emission differs from the phonon‐assisted ``edge emission'' starting at 5140 Å when observed in pure CdS in that the emission peak at 5220 Å, corresponding to the emission of onek=0LOphonon, is more intense than the zero phonon peak. The relative peak intensities of the zero phonon and phonon replicas in pure CdS can be described by a Poisson distribution inN¯whereN¯is the mean number of phonons emitted in the transition. These Gaussian‐shaped component peaks also have equal halfwidthsH. For pure CdS at 77°K values found in the literature areN¯≅0.8−1.0 andH≅0.03 eV. For the CdS films good fits could be obtained withN¯=1.1−1.5 andH=0.04−0.06 eV. However, it is also possible that the film luminescence is the superposition of two emission series. The peak position of the green emission spectrum observed at 10°K was close to that at 77°K, and an additional peak at 5040 Å was observed. The decay time of the green emission was less than 1.5 &mgr;sec at 77°K, and thermal quenching of the luminescence began around 100°K, with an activation energy of 0.15–0.17 eV. Baking in saturated cadmium vapor at 500°C quenched the green emission, and for films baked in H2S or H2S+HCl+H2at 600°C, emission similar to that observed in pure CdS was obtained. Optical absorption measurements indicated that the band edge was sharpened by the baking processes. The blue emission peak observed in the films was at 4892 Å at 77°K, which is in the fundamental absorption edge. It shifted to 4875 Å and became more intense and narrower at 10°K. This emission persists to 300°K with the peak position decreasing in energy as the bandgap. The peak is quenched by baking in H2S but not by baking in saturated Cd vapor. The blue emission is probably associated with a shallow donor or Cd excess in the films.

ISSN:0021-8979    

DOI:10.1063/1.1658575

出版商:AIP    

年代:1970

数据来源: AIP