摘要:

A method has been developed for measuring optical absorption in epitaxial semiconductors in which the layer structure is grown on a substrate of narrower band gap and opposite conductivity‐type so that the intensity of light transmitted can be monitored by measuring the photovoltage generated at the buried junction using a transparent surface contact. This arrangement provides a quick method of locating the wavelengths of features in the absorption spectrum. However, it is also possible to obtain an absolute measurement of the transmitted fraction using a control sample from which the absorbing layer structure has been removed by etching, usually a matter of etching only a few microns. This result is independent of surface reflections and the linearity and spectral response of the junction. The method is described with particular reference to GaAs/AlGaAs multiple quantum well structures, though it is also applicable to single homogeneous layers, and the experimental results are in good agreement with those obtained by conventional transmission measurements on samples from which the substrate has been removed.

ISSN:0021-8979    

DOI:10.1063/1.335948

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A contactless method for determining the spatial variation of the free carrier density in CdS is presented. The method involves the correlation of IR transmission with the free carrier density via the IR absorption coefficient. Preliminary measurements indicate a free electron density sensitivity of less than 5×1014cm−3and a spatial resolution which is limited only by the spot size of a CO2(&lgr;=10.6 &mgr;m) laser; this should be of the order of 100 &mgr;m. Experimental results indicate that the predominate scattering is due to impurity interaction at room temperature; this is indicative of the high degree of compensation in CdS.

ISSN:0021-8979    

DOI:10.1063/1.335949

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

BeO:Li and BeO:Na single crystals have been investigated by thermoluminescence (TL) techniques in the interval 10–300 K. X‐irradiated BeO:Na exhibits an intense glow peak at 85 K and a weak one near 46 K. BeO:Li displays intense glow at 72 K. Analyses of the two strong peaks (the weak one was not amenable to analysis) yield the following TL parameters:Tm=72 K,E=0.143 eV,s=1.08×108sec−1, andl=1.3;Tm=85 K,E=0.197 eV,s=1.05×1010sec−1, andl=1.2, whereEis the thermal activation energy,sis the frequency factor, andlis the order of kinetics. Spectral emission from the two intense glow peaks were similar, characterized by band emission with maxima near 320 and 525 nm. A model consistent with previous TL and magnetic resonance results which adequately describes our data is presented. It is suggested that the main glow peaks are due to holes released atVcenters whereby they recombine withFandF+centers. Recombination at theFcenter yields 525‐nm radiation whereas recombination at theF+defect produces 320‐nm emission. Optical excitation, photobleaching, and phototransfer experiments support this model.

ISSN:0021-8979    

DOI:10.1063/1.335950

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The fusion temperature (T&fgr;), the oxygen partial pressure (PO2) during melting and the quenching rate fromT&fgr;all influence the optical absorption in the 5.06‐eV (245‐nm) region. These observations are consistent with the assumption that the defect responsible for the optical absorption is an oxygen vacancy or complex of vacancies. The activation energy for the formation of the defect in GeO2glasses which is repsonsible for the optical absorption is 2.3 eV which is larger than the activation energy for oxygen diffusion (∼1 eV).

ISSN:0021-8979    

DOI:10.1063/1.335951

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A beam of Cs+ions with an energy of 500, 1000, or 2000 eV is scattered from a cesiated W(110) target. The angle of incidence is 45° or 75° with respect to the surface normal. The charge state and energy of the scattered particles are measured. The influence of hydrogen coadsorption on the final charge state is investigated. All scattered cesium particles are neutrals when the surface work function is smaller than 2.6 eV. The scattered particles have suffered a pronounced energy loss. From the measurements an extrapolation is made to conditions relevant for surface conversion negative ion sources.

ISSN:0021-8979    

DOI:10.1063/1.335952

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A model is presented for the mechanism which establishes the dynamic equilibrium cesium coverage on a W(110) converter surface in the discharge chamber of a negative hydrogen ion source. The charge state of cesium particles arriving at the converter surface is found to be a crucial parameter. A coverage greater than 0.26 monolayers cannot be maintained if the cesium component is highly ionized. The corresponding negative hydrogen ion formation probability is far from optimum. This situation is probably present in all high‐density surface conversion negative ion sources employed nowadays.

ISSN:0021-8979    

DOI:10.1063/1.335953

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The conductance of trans‐polyacetylene is measured during oxidation using an interdigital microelectrode. The measurements obtained indicate a slight increase in the conductivity during initial exposure in air and then a decrease during oxidation, which is confirmed by the corresponding changes in the infrared absorption spectra. The logarithm of conductivity is inversely proportional to the oxidation time. A proposed model which is derived from Kivelson’s theory predicts the behavior of conductivity as a function of time during oxidation. The experimental data of conductivity is in agreement with the calculated data using this model. The temperature dependence of the conductivity at certain stages also supports the theory that the electrical transport mainly occurs through intersoliton electron hopping. Thus, the electrical transport mechanism during oxidation is clarified.

ISSN:0021-8979    

DOI:10.1063/1.335954

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The process of growing large diameter single crystals of Al2O3:Ti3+by vertical solidification of the melt is described, and some of the problems in producing high‐optical quality material are discussed. The characterization of the distribution and valance state of titanium ions was performed by x‐ray techniques and laser Raman microprobe methods. The presence of other impurity ions, specifically iron, was also determined. In some cases titanium was found in the grown crystal to be in the rutile form. In addition, Ti‐Fe pairs, and concentrated regions of titanium on the surface of the boule were also observed. Some procedures for minimizing these problems are discussed. The results of optical absorption, fluorescence, and lifetime measurements are reported. The addition of Fe is shown to produce a broad absorption band in the red region of the spectrum, and two‐photon laser excitation terminating in the ultraviolet spectral region produces a broad blue emission band.

ISSN:0021-8979    

DOI:10.1063/1.335955

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The dielectric functions ofa‐Si prepared by Si ion implantation in Si and of subsequently thermally annealeda‐Si have been measured by means of spectroscopic ellipsometry. Differences are observed that may be accounted for only partially by differences in density, recrystallization during preparation of the anneal‐stabilizeda‐Si state, or differences in the surface condition of the samples. Intrinsic changes in the bond polarizability are thus indicated. Comparison of the x‐ray photoemission results for the Si 2pcore levels and the valence band states of the as‐implanted and anneal‐stabilizeda‐Si samples reveals measurable changes in the valence charge distribution sufficient to substantiate a change in the bond polarizability.

ISSN:0021-8979    

DOI:10.1063/1.335956

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The effects of inhomogeneous doping and/or composition profiles in the active regions of AlGaAs/GaAs heteroface solar cells have been studied using a realistic computer model. It is found that forn‐pdevices with moderate surface recombination velocitiesS, only modest improvements in the cell efficiency are obtained by including linear or exponential profiles. Such gradients become more valuable, however, whenever (1)Sincreases, (2) the solar illumination is increased through concentration, or (3) ap‐ndevice is desired.

ISSN:0021-8979    

DOI:10.1063/1.335957

出版商:AIP    

年代:1985

数据来源: AIP