摘要:

The field‐induced strain characteristics have been investigated for a sequence of La‐modified lead zirconate titanate (PLZT) compositions. It was shown that the increase in the ease of polarization switching is essential for maximum electrically induced strains in PLZT ceramics. For PLZT compositions close to the morphotropic phase boundary this was realized by adjusting the base composition to be close to the boundary between tetragonal and rhombohedral states, where the polarization has a maximum number of equivalent orientations (6 for tetragonal plus 8 for rhombohedral) by which to switch. For PLZT compositions located in either the rhombohedral or tetragonal states, the ease of polarization switching was facilitated by La doping until the point where the normal micron‐sized ferroelectric domains began to break up into tweedlike subdomain structures. Polarization switching may then occur through the subdomain state, rather than by the creation and subsequent motion of normal micron‐sized domain boundaries. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361056

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The effects of arbitrary substrate orientation on the electronic and optical properties of III‐V zinc‐blende semiconductors are considered. A unitary transformation matrix is used to rotate the 4×4 Luttinger valence band Hamiltonian, and the Bir‐Pikus strain Hamiltonian from the conventional (001) surface to any arbitrary (hkl) surface of interest. The effects of strain on several electronic and optical properties are examined. It is found that the strain‐induced change in the forbidden gap is largest for the (111) plane and other equivalent planes. Furthermore, the strain is also found to induce both a longitudinal and a transverse piezoelectric field. The longitudinal field reaches a maximum for the (111) surface and its other equivalent planes, while the transverse field reaches a maximum for the (110) surface and its other equivalent planes. The orientation‐dependence of the hole effective masses is also examined; it is found that the (111) surface, and other equivalent planes, exhibits the largest heavy‐hole mass among all possible planes. Finally, this article examines the effects of orientation on the optical transition matrix elements. For incident light with in‐plane polarization vectors, the matrix elements are, in general, anisotropic—with the largest anisotropies predicted for two new surfaces: the (&sqrt;310) and the (1&sqrt;30) surface. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361057

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A detailed comparative study of the optical properties of two rare‐earth (RE) sesquisulfide compounds &ggr;−Ce2S3and &ggr;−Gd2S3, shows that if the two compounds have about the same main absorption edge corresponding to band‐to‐band S 3p‐RE 5dtransitions, Ce2S3exhibits an additional absorption band at lower energies. This band, which is ascribed to the presence of Ce 4fstates at the top of the valence band, explains the difference in color between the two compounds. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361058

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Photoreflectance (PR) spectroscopy has been developed as a powerful technique for the characterization of the heteroepitaxial layer of the Cu–III–VI2semiconductors having the chalcopyrite structure. PR measurements have been carried out in the energy region near the fundamental absorption edge at 77 K for the heteroepitaxial layers of CuAlSe2, CuGaSe2, CuGaS2, and CuAlS2grown on GaAs and GaP substrates by means of the low‐pressure metalorganic chemical vapor deposition. Crystal quality, stress, and the crystallographic orientation have been well characterized, based on the analysis of the PR spectra in terms of transition energy, intensity, and broadening parameter. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361059

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Waveguided Raman measurements have been performed in order to detect the presence of Ag nanoclusters in soda‐lime glass waveguides obtained by ion exchange. By subtracting a strong broadband luminescence and the Raman contribution of the glass matrix, a low frequency Raman peak is resolved. The peak is ascribed to surface acoustic vibrations of silver clusters. The involved modes are the quadrupolar spheroidal ones. The size distribution of the Ag clusters is deduced from the energy and the linewidth of the peak. Silver particles have small dimensions with an upper size limit of about 1.5 nm. This result is in good agreement with recent transmission electron microscopy measurements. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361060

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Sulfur‐ (ntype) and magnesium‐ (ptype) doped InGaP layers grown by liquid‐phase epitaxy are investigated by low‐temperature photoluminescence (PL) measurements in the energy range between 1.55 and 2.25 eV (800–550 nm). The PL spectrum of nominally undoped InGaP epilayer shows four different peaks. Besides a bound exciton recombination peak, three longitudinal optical‐phonon replicas with one superimposed donor–acceptor emission are identified based upon their dependence of emission energies on temperature and excitation intensity. For heavily sulfur‐doped epilayers, the transition peak from the conduction‐band filling level shifts toward higher energy with increasing electron concentration. However, the near‐band‐edge emission peak shifts toward lower energy with increasing hole concentration due to band‐gap shrinkage in magnesium‐doped epilayers. A near‐band‐edge radiative emission mechanism is also proposed to explain the observed phenomena. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361061

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The optical constants, such as the complex dielectric function, complex refractive index, absorption coefficient, and normal‐incidence reflectivity, of Pb1−xSnxTe alloys have been determined using spectroscopic ellipsometry in the 1.15–5.5 eV photon‐energy range at room temperature. The dielectric‐function spectra [&egr;(E)] and their second‐derivative spectra [d2&egr;(E)/dE2] were analyzed using a simplified model of the interband transitions. The composition dependence of the critical‐point parameters and high‐frequency dielectric constant has been obtained from these analyses. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361062

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Nitrogen acceptors confined in a CdZnTe single quantum well, grown by molecular beam epitaxy, are investigated by different optical methods. The transitions related to nitrogen acceptors confined in the well are observed in the doping range between 1017and 1018/cm3. The temperature and excitation intensity dependence of the nitrogen‐related transitions in photoluminescence spectra indicates that these transitions correspond to the nitrogen acceptor bound excitons and to free electron to neutral nitrogen acceptor recombination. The binding energy of nitrogen acceptors confined in an 130‐A˚‐wide Cd0.96Zn0.04Te/Cd0.86Zn0.12Te structure is deduced to be 51.7±0.5 meV from this study. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361063

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Thick (∼1.3 &mgr;m) oxide films were grown by room‐temperature oxidation of silicon after low‐energy copper‐ion implantation. The structural properties of the silicon dioxide layer and the implanted silicon were characterized by Rutherford backscattering spectrometry and transmission‐electron microscopy. During the room temperature oxidation a portion of the implanted copper resided on the surface and a portion moved with the advancing Si/SiO2interface. This study revealed that the oxide growth rate was dependent on the amount of Cu present at the moving interface. The surface copper is essential for the dissociation of oxygen at the surface, and it is this oxygen that participates in the oxidation process. The resulting oxide formed was approximately stoichiometric silicon dioxide. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361064

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A comparative study has been made of the structures and magnetic properties of Nd10Fe84B6prepared by mechanical alloying using elemental powders as starting materials and by mechanical milling of the alloy. Both milling procedures resulted in a mixture of &agr;‐Fe and an amorphous phase, with the fraction of &agr;‐Fe phase being significantly higher in the as‐milled mechanically alloyed powder than in the mechanical milled counterpart. Annealed mechanically alloyed powders showed a somewhat coarser and nonuniform grain structure in comparison with annealed mechanically milled powders. The structural differences of mechanically milled and mechanically alloyed powders resulted in higher remanences and coercivities being exhibited by the mechanically milled powders after annealing. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361065

出版商:AIP    

年代:1996

数据来源: AIP