摘要:

Er-doped GaAs codoped with oxygen was studied by site-selective measurements of photoluminescence spectra and photoluminescence-excitation spectra directly exciting the4f-shell electrons of one kind of Er center at a time. Within one sample, more than 10 kinds of distinctly different Er centers, showing different Er-related spectra, were observed, although its host-excited photoluminescence spectrum is dominated by the luminescence from one kind of Er center. The atomic configuration of that center has been identified as an Er atom located at the Ga sublattice with two adjacent oxygen atoms (Er-2O center). Seven kinds of Er centers in GaAs:Er, O and two kinds of Er centers in AlGaAs:Er, O were studied in detail. The numbers of lines and the magnitudes of energy separations among the lines in each spectrum indicate that the Er atoms of all nine kinds of centers are coupled with oxygen atoms and have noncubic symmetry. The nine Er centers were grouped into several classes according to similarities in their spectra which should reflect symmetries of the Er centers. The atomic configurations of two classes of Er centers are discussed in detail. The Er centers of both classes have a nearest-neighbor site atomic configuration similar to that of the Er-2O center with a symmetry close to rhombicC2v,but Er centers in the two classes have different types of deviation fromC2vdue to the difference in the second-nearest-neighbor atomic configurations of the Er atoms. We also discuss a large difference in the efficiency of the Er-related luminescence under host photoexcitation caused by the difference in the second-nearest-neighbor atomic configurations. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365709

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Thresholdlike behavior of photoluminescence (PL) in heterostructure wafers is studied. It is shown that strictly speaking there is no PL threshold, and the thresholdlike dependence of PL on the pump power results from the combination of three factors: the PL spreading along the wafer surface, the change in the radiative fraction of electron-hole recombination, and the restricted aperture of the PL detector. The first two factors were found to be dominating in the wafers studied. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366250

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Extrinsic photoresponse spectra(T=300 K)and photoluminescence spectra(T=77 K)ofCuInSe2single crystals grown with the deviation from valence stoichiometry are studied for point defect identification. The main peaks of photoresponse and photoluminescence correlate each other. The characteristic spectral singularities at 1.00, 0.98–0.97, 0.94, 0.92–0.89, and 0.72 eV have been attributed to photoactive and radiative transitions through the donor(VSe,InCu)and acceptor(VCu,CuIn,Sei)levels. The shift of the extrinsic photoresponse peak to long wavelengths(0.92→0.89 eV)by theVSepoint defect has been found at increasing deviation from valence stoichiometry&Dgr;Z<0.The impurity subband formation has been suggested as very probable in the crystals with elevated&Dgr;Z.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365710

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Photoluminescence, Raman, and Hall measurements are reported for Mg doped GaN films grown by molecular beam epitaxy. The compressive and tensile stress determined by the Raman shift of the phonon lines is due to the growth conditions rather than the presence of Mg in the film. The photoluminescence peak of near band-to-band transitions is also shifted to larger (smaller) energies by the compressive (tensile) stress. The study of the longitudinal optical phonon of theA1branch shows that its Raman line shape is affected mostly by the crystalline quality of the film. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365711

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Photoluminescence (PL) of Te-doped In0.5Ga0.5P epilayers grown by the liquid phase epitaxy technique has been investigated as a function of carrier concentration. The PL results are interpreted using a model taking into account nonparabolicity of the conduction band. Both the band filling as well as band tailing due to the Coulomb interaction of free carriers with ionized impurities and band shrinkage due to the exchange interaction between free carriers are considered in order to properly portray the observed features of the PL spectra. The theoretical calculations are in satisfactory agreement with the observed PL results. The PL line shape is well explained by a direct transition with a simplek-selection rule up to a carrier concentration of 2.0×1018cm−3. Above the carrier concentration of 2.0×1018cm−3, on the other hand, it is properly interpreted in terms of non-k-conserving transitions that arise from the indirect recombination of electrons in a highly filled conduction band. It was found that a concentration dependent gap shrinkage due to the exchange interaction in Te-doped In0.5Ga0.5P at 17 K is described by the relationEce=2.34×10−8n1/3(eV). The concentration dependent effective mass has also been calculated using Kane’s three band model. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365754

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The electroluminescence (EL) from Si+implanted SiO2thin film prepared by thermal oxidation was compared with photoluminescence (PL) properties. Both EL and PL spectra indicate that the luminescence originate from the same three luminescence bands around 470, 600, and 730 nm. Annealing at temperatures below and above 1000 °C makes the 470 and the 730 nm bands dominate in PL spectra, respectively. The 600 nm band, which is weaker in PL, is usually the strongest in EL. The relative contributions from different luminescence bands to EL depend on annealing, but are independent of current density. The different excitation mechanisms of the 470, 600, and 730 nm luminescence bands give rise to the discrepancy between EL and PL. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365712

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Ultrafast measurements of photoexcited carrier dynamics within a 60 nm subsurface of a crystalline silicon wafer were carried out using subpicosecond transient reflectivity. A uv pump light was employed to restrict carrier generation to occur within the subsurface by direct interband transitions. Carrier diffusion was found to be suppressed in the subsurface region of the intrinsic silicon wafer. For ion-implanted silicon wafers, heat was generated within a few picoseconds after the laser irradiation. By scanning a partially ion-implanted silicon wafer, the two-dimensional image was obtained, which showed that time-resolved imaging can separately map photoexcited carrier density and transient temperature rise. The possibility of three-dimensional process monitoring was considered as well. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365713

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We show that in interpreting the conoscopic interference fringes, one should exercise care in employing approximate expressions which fail for certain crystal cuts. In this paper, we study64°- and128°-rotatedY-cut andZ-cut LiNbO3wafers. We show that the error made in using the approximate formulae for the samples is more than 25&percent; and that one has to use exact formulae in order to attain quantitative agreement with the experimental data. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365755

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Optical properties of diluteFe1−xSix(x⩽0.1)alloys were studied by spectroscopic ellipsometry in the 1.5–6 eV photon energy region. The absorption strength of the alloys is found to decrease in the entire energy region as the Si composition increases. The interband-transition edges of Fe at about 2.5 eV in the minority-spin bands and at about 5 eV in the majority-spin bands shift to lower energies as the Si composition increases. The decrease in the absorption strength is interpreted as due to a decrease in the density of states of the Fe host and also due to a reduction of conduction-electron concentration in the alloys. The shifts of the 2.5 and 5 eV interband-transition edges can be explained in terms of a perturbative variation in the band structure of Fe induced by its alloying with Si. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365756

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have studied the electron emission characteristics of the hydrogen-free diamondlike carbon (DLC) and conventional DLC films. The electron emission current of conventional DLC increases at first and then decreases continuously with bias stress time. The emission current of the hydrogen-free DLC, deposited by the layer-by-layer technique, increases at first and then stabilizes with increasing stress time. The resistivity of the hydrogen-free DLC decreases after long bias stress, and that appears to be due to the changes in the density of states in the gap of the hydrogen-free DLC. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366286

出版商:AIP    

年代:1997

数据来源: AIP