摘要:

The electronic states of vapor‐deposited materials used in electroluminescent devices were measured by ultraviolet and x‐ray photoelectron spectroscopy, UV‐visible absorbance, and photoluminescence spectroscopy. The combination of these measurements on ultrathin films of these materials allows (1) the determination of the energy (with respect to vacuum) of the highest occupied molecular orbital (HO) and the ionization potential (IP), and (2) the estimation of the lowest unoccupied molecular orbital (LU) energy and an approximation of the electron affinity, (EA). The knowledge of the binding energies of these states is important for the understanding of light‐emitting diode properties and the potential optimization of such devices. The luminescent material tris(8‐hydroxy‐quinoline) aluminum has an IP of 5.9 eV and an apparent EA smaller than 3.5 eV. The IP of both hole transport agents, tri‐p‐tolylamine and 1,1‐bis(4‐di‐p‐tolylaminophenyl)cyclohexane, is 5.4 eV and their EA is estimated to be smaller than 1.8 eV. The electron transport agents 2‐(4‐biphenyl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole, 2‐t‐butyl‐9,10‐n,n’‐dicyano‐anthraquinonediimine and dicyano‐diphenylsulfone differ in IP from 7.1 to 7.6 eV and the EA for these materials are estimated to be smaller than 3.5, 4.9 and 5.5 eV, respectively. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.359685

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A detailed characterization of the impurity centers involved in the photoluminescence (PL) ofp‐type CdTe doped with arsenic (As) and antimony (Sb) has been performed. The PL spectrum has been measured from 1.35 eV up to the band edge and as a function of temperature (4.2 up to 30 K). In addition to the familiar broad PL line centered at 1.45 eV and present in undoped and doped materials, the doped samples exhibit a new band near 1.54 eV showing a fine structure composed of two peaks whose intensities vary with temperature. The observed longitudinal optical (LO) phonon replicas associated with the zero‐phonon lines, at 1.45 eV and 1.54 eV, respectively, are characterized by a Huang‐Rhys factorS=1.3±0.1 andS=0.30±0.02. The various electron‐hole recombination processes are explained by means of a simple analytic model correlating the position of the zero‐phonon lines to the relative intensities of the phonon side bands. The model accounts for the chemical shift of the defect centers and describes the effect of the charge carrier LO‐phonon interaction in the framework of the adiabatic approximation within the envelope function approach. Comparison between theory and experiment leads to the following values for the effective Bohr radii:aAs=(10.6±0.1) A˚,aSb=(10.3±0.1) A˚, and ionization energies:EAs=(58±2) meV,ESb=(61±2) meV. It also leads to conclude to the presence of native shallow donors with binding energyED=(13±2) meV and of deeper native acceptor complexes with effective Bohr radiusaA=(6.1±0.1) A˚ and ionization energyEA=(157±2) meV. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359686

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

This article suggests an alternative mechanism for electron emission from the ferroelectric ceramic cathode. This mechanism involves the concept of vacuum breakdown initiation from metal‐dielectric cathodes that comprises two stages: the field emission through metal‐ dielectric‐vacuum conjunction followed by the processes resulting in an uncompleted surface discharge. The electron emission thus occurs from the low‐density surface plasma. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359687

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We investigated the potentiality of a phosphorus‐doped silicon oxide (SiO:P) carrier‐free disordering source for applications in photonic devices integration schemes. This is accomplished in three successive steps by employing an InGaAsP/InGaAsP structure with compressively strained wells and lattice‐matched barriers designed for operation around ∼1.55 &mgr;m. First of all, we showed that the SiO:P encapsulant offers a good control over a wide range of disorder (blue shifts as high as ∼150 meV). Later on, the high optical quality of the disordered regions is demonstrated by detecting 300 K excitonic features in moderately blue‐shifted (∼40 meV) samples. And, finally, a first attempt of its application in integration technology is made by realizing a monolithic composite of a distributed feedback laser and a quantum‐confined stark effect electroabsorption modulator operating around 1.54 &mgr;m. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359688

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have investigated the far‐infrared reflectivity spectra of two series of InAs/GaSb superlattices grown with GaAs‐ or InSb‐like interfaces. Significant differences in the spectra induced by the interface bond type can be observed. The theoretical simulation of the experimental data allowed us to accurately determine the energy of the interface TO phonons and the actual thickness of the region in which they are localized. The inactivity of the InAs TO phonon vibration at the interface can be explained by modeling a nonhomogeneous strain accommodation across the heterointerfaces. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359689

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Ellipsometric studies in the energy range 1.5–5 eV have been performed on thin films of Cd1−xMnxTe deposited by sublimation from alloys prepared by melt quenching. The spectra showE0,E1, andE1+&Dgr;1transitions of cubic semiconductors. The changes in peak positions under influence of HeNe laser light, small alternating magnetic field, and under the influence of both applied simultaneously have been investigated. Shifts in peak positions observed for all the three transitions have been interpreted on the basis of changes in the band structure of Cd1−xMnxTe thin films at these critical points. This has been corroborated by theoretically calculating the effective number of electrons contributing to transition per atomNeffand the density‐of‐states data. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359690

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Photoluminescence, photoconductivity, and Hall measurements were performed over a large range of temperature (13–300 K) for various crystals of the electro‐optical semiconductor CdIn2Te4. Crystals are compensated semiconductors with a high donor–acceptor pair concentration assigned to the disorder in the cation sublattice. The inhomogeneities in the distribution of the donor–acceptor pairs and point defects, due to the lack of stoichiometry, result in band fluctuations, and thus in carrier localization effects, at low temperature. This is suggested by the photocurrent transient responses and the dependence of the luminescence intensity versus the excitation level. The nonhomogeneous distribution of point defects in off‐stoichiometry crystals is observed by the deep level transient spectroscopy technique. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359691

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Photoinduced absorption (PA) of hydrogenated amorphous silicon (a‐Si:H) was studied by excitation spectra analysis. The nonlinear PA response taken at different excitation photon energies was found to follow the corresponding absorption coefficient for intrinsic andp‐doped samples in the 80–300 K temperature range. Significant contribution of the electronic PA in the observed response was demonstrated. Thermal effects are discussed. A simple model of trapping during the pump with consequent recombination from the localized state was found to be in good agreement with experimental observations. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359692

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The longitudinal (LA) and transverse (TA) Brillouin spectra along [001] phonon direction have been measured as a function of temperature (50–475 K) in single‐crystal PbMg1/3Nb2/3O3with scattering angles &thgr;s=180° and 32.5±0.2°. The Brillouin frequency shift with decreasing temperature shows a broad softening anomaly for both LA and TA phonon modes. For &thgr;s=180°, a gradual growth in damping with maximum near 270 K is observed and is attributed to order parameter fluctuations. An additional Landau–Khalatnikov maximum is also observed atTc∼212 K. This anomaly implies a rapid growth of ferroelectric ordering nearTcand is consistent with the earlier linear birefringence results reported by Westphaletal. The elastic stiffness and compliance constants,CE11,CE44, andsE44are also determined between 200 and 370 K. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.359622

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Photoluminescence studies from 5 to 296 K have been performed on a series of iodine‐doped CdTe epilayers grown by molecular beam epitaxy. The samples exhibit excess electron concentrations in the range from 8×1016to 3×1018cm−3. Bright edge emission is observed at 296 K from all samples. A deep‐level band centered near 1.45 eV is observed atT<210 K and increases in intensity with doping level. A correlation of growth parameters with photoluminescence data fits a model of the deep‐level band being predominantly donor‐acceptor pair recombination involving the shallow iodine donor (ITe) and the iodineA‐center acceptor complex (VCd‐ITe). Zero‐phonon emission related to this pair recombination occurs at 1.470 eV at 5 K. Thermal quenching of the integrated intensity of this donor‐acceptor band is described by activation energies of 15 and 125 meV corresponding to thermalization of electrons from shallowITedonors to the conduction band and complete thermalization from the valence band to iodineAcenters, respectively. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359623

出版商:AIP    

年代:1995

数据来源: AIP