摘要:

Investigations of the polarization mechanisms in tungsten bronze relaxor ferroelectrics, Pb1–xBaxNb2O6(PBN[(1−x) %]), in particular, of the morphotropic phase boundary compositions have been carried out for both ceramics and bulk crystals by means of electrical, thermal, optical, and electron‐microscopic methods. Relations of phase‐transition behavior with compositional and polarizational fluctuations have been carefully studied. Instead of a sharp boundary composition, it is found that a rather wide composition range, 1−x≊0.63±0.03 in Pb1−xBaxNb2O6, corresponds to the orthorhombic and tetragonal morphotropic phase boundary. It is demonstrated with the help of optical conoscopic interference figures that for the near‐morphotropic phase boundary single crystal PBN of tetragonal symmetry, the polarization vector can be switched orthogonally to an orthorhombic phase simply by the application of an electric field, which authenticates optically the 90° polarization rotation. A transmission electron microscope study in the temperature range from −180 °C to room temperature revealed the presence of incommensurate ferroelastic domains in the morphotropic phase boundary composition PBN crystals. In light of the above observed experimental data, the polarization mechanisms of the morphotropic phase‐boundary compositions are discussed in terms of qualitative thermodynamics.

ISSN:0021-8979    

DOI:10.1063/1.345651

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Metal‐oxide‐silicon (MOS) capacitors used in the breakdown mode were constructed to detect252Cf fission fragments. The physical effects related to radiation‐induced breakdown were studied and found to have a relationship to intrinsic dielectric breakdown. Physical studies were made of the effect of oxide annealing temperature between 100 and 400 K, oxide thickness, differing metal electrodes, and the materials interaction due to the spark discharge breakdown. By means of both silicon‐ion and cesium‐ion implants near the metal‐SiO2interface of the MOS capacitor, the current emission into the SiO2was found to be significantly enhanced; however, the enhanced emission was found to have no effect on increasing the sensitivity to lower specific ionization radiation as seen by fission‐fragment detection. The results indicate that the radiation‐induced breakdown mechanism occurs within the bulk, or body, of the SiO2film and is not influenced by conditions at the dielectric interfaces. It was found that thin films of the refractory metals HfO2or ZrO2between the oxide film and a top aluminum electrode prevented Al‐SiO2interaction during discharge and allowed operation of the MOS capacitor at higher electric fields. Obtaining higher operating fields significantly improved the minimum specific ionization detectability to 14 MeV cm2/mg from a prior value of 22 MeV cm2/ mg.

ISSN:0021-8979    

DOI:10.1063/1.345652

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Room‐temperature photoreflectance measurements were used to determine the radial and axial distribution of low levels of indium in 3‐in.‐diameter semi‐insulating bulk GaAs materials grown by the liquid‐encapsulated Czochralski method. These results were compared with 4.2‐K photoluminescence data and found to be accurate and more convenient for this application. Room‐temperature photoreflectance allows an accurate determination of the indium content in the range of mole fraction 0.1%–2.0% with standard deviation of 0.03%. Two types of radial inhomogeneity were found in commercially available GaAs wafers. This is discussed in terms of indium segregation and shape of solid and liquid interface during the crystal growth.

ISSN:0021-8979    

DOI:10.1063/1.345653

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have recently reported the formation of color centers in stabilized cubic zirconia (ZrO2, 18% Y2O3) by two‐photon absorption at 532 nm. Here we present the results of measurements of the transmission of the colored samples as a function of time at room temperature. The results are found to be in good agreement with theory that assumes the color centers diffuse out of the irradiated region. The initial distribution of centers is assumed to have a Gaussian profile. For this model, the diffusion equation was solved exactly and the diffusion constant obtained (∼3.4×10−8cm2/s).

ISSN:0021-8979    

DOI:10.1063/1.345654

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have characterized Czochralski‐grown undoped AlSb single crystals by low‐temperature photoluminescence and photoluminescence excitation spectroscopy. An excitonic band‐gap energyEgx=1.667±0.001 eV of AlSb was determined. In all samples we detect a dominant donor and acceptor. The donor binding energyED=151±3 meV and acceptor binding energyEA=37±3 meV are deduced from donor‐acceptor pair luminescence and the excited states of the acceptor from selective pair excitation. We tentatively identify the donor as sulfur and the acceptor as carbon.

ISSN:0021-8979    

DOI:10.1063/1.345655

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Several novel features are observed in the low‐temperature photoluminescence spectra of AlxGa1−xAs layers grown on GaAs by metalorganic chemical vapor deposition. GaAs substrate luminescence spectra are observed through AlxGa1−xAs layers as thick as 22 &mgr;m. Both carrier diffusion to the substrate and AlxGa1−xAs luminescence are identified as the excitation mechanisms of the GaAs luminescence, and a minority‐carrier diffusion length of 10 &mgr;m is estimated. The presence of photon recycling in the AlxGa1−xAs layers is demonstrated by comparison of photoluminescence (PL) spectra for layers with and without GaAs substrates, as well as PL examination of two AlxGa1−xAs heterostructures.

ISSN:0021-8979    

DOI:10.1063/1.345656

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A novel method of calibrated doping of Mn in ZnS thin films has been used to study room‐temperature cathodo‐ and photoluminescence characteristics of ZnS:Mn films for a Mn concentration range of 0.07–26.4 wt. %. It was observed that the luminescent intensity increases with Mn concentration up to ∼2 wt. %, beyond which intensity decreases. Emission spectra revealed a lower energy peak in addition to the 580‐nm yellow peak for higher dopant concentration. The occurrence of this red peak and quenching of yellow emission is probably at approximately the same activator concentration (∼2 wt. %). We attribute these to the phenomenon of energy transfer to energy sinks via unexcited Mn.

ISSN:0021-8979    

DOI:10.1063/1.345657

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A numerical Kramers–Kronig analysis is used to calculate the refractive‐index change &Dgr;ncaused by the injection/depletion of free carriers in various dopedn‐type GaAs. The analysis makes use of a carrier‐related absorption spectrum, which is established by using quantum theory as well as empirical relations and is confirmed by the experimental absorption data in the literature. We obtain the &Dgr;nvalues for various doping concentrationsNDand carrier concentrationsNat three wavelengths; &lgr;=1.06, 1.3, and 1.55 &mgr;m. The &Dgr;nvalue is positive for low‐Nregion, and increases gradually to its maximum which is around 10−4for &lgr;=1.06 &mgr;m. Thereafter, &Dgr;ndecreases rapidly to 0 asNincreases. The linear relation between &Dgr;nandN, as predicted by the Drude theory, only happens whenNis beyond a certain value. In this region, the &Dgr;nvalue may attain to −10−2atN=5×1018cm−3for &lgr;=1.55 &mgr;m. Because of this significant &Dgr;nvalue and its linear relation withN, the free‐carrier induced index‐change effect may find the applications in integrated optics and optical probing.

ISSN:0021-8979    

DOI:10.1063/1.345658

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A surface charging technique used in conjunction with x‐ray photoelectron spectroscopy (XPS) has been applied as aninsitusurface analytical tool for the studies of the fabrication of dielectric‐semiconductor structures. It was found that the measurements of surface composition and Fermi level position by XPS gives useful information on the effects ofinsitusurface modification prior to the deposition of the dielectric film and on the properties of the dielectric‐semiconductor structure. When the thin dielectric film thickness is within 10 nm, XPS yields information on both the dielectric film and the semiconductor at the interface, and thereby allows the monitoring of the initial growth of the dielectric film. In addition to this conventional approach, surface charging of the thin dielectric film during XPS analysis, either by photoemission or by flooding the surface with low‐energy electrons, provides additional information on Fermi level stabilization of the semiconductor at the insulator‐semiconductor interface. Furthermore, the charging potential associated with a local impurity in the sample structure can be used to estimate the depth location of the impurity. The measurement of the degree of charging also gives information on the electrical properties of the dielectric.

ISSN:0021-8979    

DOI:10.1063/1.345659

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A semiempirical function for the energy‐loss distribution of nonrelativistic electrons is presented. The form of the distribution function permits analytic sampling of the energy loss and is, therefore, suitable for Monte Carlo electron transport codes developed for small microprocessor computer systems. Comparisons between calculated transmitted energy distributions using a microprocessor and experimental results are presented for 15–20‐keV incident electrons on aluminum, copper, and gold foils.

ISSN:0021-8979    

DOI:10.1063/1.345660

出版商:AIP    

年代:1990

数据来源: AIP