摘要:

For the investigation of polarization distributions in pyroelectric materials, the laser intensity modulation method (LIMM), which is based on thermal waves, is widely used. With this method, the sample under investigation is heated by the absorption of intensity modulated light at one surface, while the pyroelectric current is measured. The thermal excitation generates a thermal wave penetrating into the sample. The penetration depth is varied with the modulation frequency. A new procedure for the reconstruction of the polarization distribution from a measured pyroelectric current spectrum is introduced. This procedure is especially well suited for polarization probing near the sample surface. An approximation for the polarization distribution is calculated from a measured pyroelectric spectrum in a very simple and direct way, avoiding mathematical instabilities. The calculation can be performed during the measurement of a pyroelectric current spectrum. This makes LIMM an on‐line procedure. The new technique of analysis is applied to the measurement of thin depolarized layers near the surface of homogeneously poled ferroelectric polymer films.

ISSN:0021-8979    

DOI:10.1063/1.351975

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Variations in the concentrations and distributions of the OH−defects present in flux and hydrothermal KTiOPO4(KTP) crystals, measured by infrared spectroscopy of single crystals, are attributed to differences in the growth environments and other nonhydrogenic defects present in the crystals. The concentrations of OH−have been estimated from the infrared data to be approximately 400 ppma (parts per million atomic) (3.0×1019cm−3) in the flux crystals, 1100–1500 ppma (0.74–1.1×1020cm−3) in the high‐temperature hydrothermal and 600 ppma (4.3×1019cm−3) in the low‐temperature hydrothermal crystals. A 3566 cm−1peak and a 3575 cm−1band are observed in all crystals. The integrated intensity of the OH−absorption band at 3566 cm−1increases at the expense of the 3575 cm−1band at higher temperatures in the high‐temperature hydrothermal crystals. Several OH−peaks (3490, 3455, 3428, 3420, and 3333 cm−1), which have strongly temperature‐dependent linewidths, are present in the hydrothermally grown KTP crystals. The temperature dependencies of their peak frequencies and widths are consistent with the presence of mobile protons in the lattice. The protons located in the 3490 and 3428 cm−1sites are believed to contribute to the ionic conductivity of the high‐conductivity high‐temperature hydrothermal crystals.

ISSN:0021-8979    

DOI:10.1063/1.351976

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Gallium doped zinc oxide films have been deposited in the temperature range 150 to 470 °C from 0.05% diethyl zinc, 0.8% water, and various triethyl gallium concentrations. The films are polycrystalline with crystallite sizes varying between 275 and 500 A˚ for undoped films and between 125 and 400 A˚ for doped films. Only those films deposited above 430 °C are highly oriented and have theircaxes perpendicular to the substrate plane. The electron density, conductivity, and mobility always increase with temperature. Thicker films have higher conductivity and mobility than thinner films. The refractive index is reduced from 1.96 to 1.73 when the electron density is increased from zero to 3.7×1020cm−3. For films deposited at 370 °C with a gallium concentration of about 2.5 at. %, the ratio of conductivity to visible absorption coefficient increases from 0.03 to 1.25 &OHgr;−1when the film thickness increases from 0.11 to 1.2 &mgr;m. A film deposited at 470 °C with a gallium concentration of 2.4 at. % and a thickness of 0.66 &mgr;m has a sheet resistance of 3.6 &OHgr;/square and an average visible absorption of 6.8%. When the gallium concentration is less than 5.0 at. %, the band gap widening approximately follows the Burstein–Moss relation.

ISSN:0021-8979    

DOI:10.1063/1.351977

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The semiquantitative analysis of optical absorption for interstitial oxygen in silicon was carried out using the molecular orbital theory and compared with results from Fourier transform‐infrared equipment having a high resolution of 0.05 cm−1. Six finely split peaks were observed with the wave numbers of 1120.2, 1123.6, 1128.3, 1132.8, 1133.5, and 1136.4 cm−1at 30 K, among which 1120.2, 1132.8, and 1133.5 cm−1were newly observed. It is concluded that there seems to be a reliable correlation between the observed band splitting and the likely energy transitions from anS6symmetry model. Fine splitting of the absorption peaks at low temperature indicates the close relationship between the local Si—O—Si bond and six nearest neighbor silicon atoms formingS6symmetry. Absorption peaks also were narrower and higher as the measurement temperature was lowered. Hence, it can be said that low‐temperature measurement improves the oxygen detectability by a factor of 10 compared with measurement at room temperature.

ISSN:0021-8979    

DOI:10.1063/1.351978

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The dependence of the photoluminescent properties of In0.48(AlyGa1−y)0.52P alloys (0≤y≤0.5) on growth temperature and substrate misorientation off GaAs(100) has been studied. Samples were grown using low‐pressure metalorganic vapor phase epitaxy. By studying the dependence of ordering behavior in InGaP as a function of substrate misorientation and growth temperature simultaneously, a very large range in low‐temperature photoluminescence emission energy—135 meV—has been obtained. The photoluminescence linewidth exhibits a strong, continuous dependence on the extent of atomic ordering (the emission energy) in the alloys. The results indicate that inhomogeneity in the microstructure of the material (i.e., between ‘‘ordered’’ domains and the ‘‘disordered’’ matrix) is the dominant photoluminescence broadening mechanism. This investigation has allowed a significant optimization of the optical properties of these materials, including the narrowest low‐temperature photoluminescent linewidths reported for all of the In(AlyGa1−y)P alloys exhibiting direct band gaps (4.2 meV for InGaP).

ISSN:0021-8979    

DOI:10.1063/1.352354

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The cross section of electroluminescent (EL) porous silicon layers (LEPOS) made fromn‐ andp‐doped silicon has been investigated by means of micro‐Raman and photoluminescence (PL) spectroscopy to find the luminescence active zone in LEPOS. Special care has been taken to avoid the heating of the sample. Additionally an energy dispersive spectroscopy scan over the sample cross section has been performed forn‐LEPOS to detect the distribution of oxygen. Since thensamples display much better EL properties than thepsamples, the investigations concentrate on thensamples. Forn‐LEPOS, a layered structure has been found with SiOx/Si at the top followed by a PL active layer. There are two types of samples showing different forms of Raman spectra. Type‐I spectra are narrow and shifted by small values as compared with the Raman spectra of bulk silicon. They have a shoulder at about 510 cm−1only in the PL active layer. Type‐II spectra are broad and shifted by about 7–10 cm−1. All the electroluminescent samples show Raman spectra of type I.

ISSN:0021-8979    

DOI:10.1063/1.351979

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The relaxation of the electron temperature in CdSxSe1−xwas measured by transmission and transient grating experiments using fs light pulses. As compared with ordinary ambipolar diffusion, at high excitation a pronounced delayed rise and a faster decrease of the diffraction signal was observed. A theoretical model that includes one‐ and two‐photon excitation, gap shrinkage, diffusion, and temperature relaxation explains these experimental findings as a result of temperature relaxation with a characteristic time constant of 1±0.2 ps.

ISSN:0021-8979    

DOI:10.1063/1.351980

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We report a strong ac green electroluminescence (EL) in powder layers of terbium doped gadolinium oxysulfide (Gd2O2S:Tb) with methyl methacrylate as binder. An intensity of the order of 30 nits (Cd/m2) has been achieved. The EL emission spectra shows line emissions corresponding to5D3and5D4fluorescing levels of Tb3+ions. A very sharply risingB‐Vcurve normally related to insulator‐phosphor interface properties of a thin film electroluminescent device has been observed in these cells. This indicates the possibilities of barrier formation due to the localized space charge region in the absence of any prominent interfaces leading to impact excitation of Tb3+ions. This has further been confirmed by the excitation spectrum of Gd2O2S:Tb phosphor, which reveals Tb3+impurity absorption bands related to 4f8shell transitions.

ISSN:0021-8979    

DOI:10.1063/1.351981

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A new Ga0.5In0.5P light‐emitting diode (LED) with order/disorder/order (DOD) structure has been fabricated by metalorganic chemical vapor deposition. Growth temperature and dopant concentration were successfully used as growth parameters to obtain a heterojunction‐equivalent structure. From the 77 K photoluminescence measurement, three peak energies of the DOD structure can be resolved clearly. It is shown that the DOD structure is equivalent to the double‐heterojunction structure. The wavelength of the LED occurring at 667 nm coincides with the ordered active layer emission. The light intensity of the DOD LED is seven times stronger as compared with that of the homojunction disordering LED at the injection current of 10 mA. These results demonstrate that the DOD structure can provide good electrical and optical confinements and can be served as heterojunction‐equivalent applications.

ISSN:0021-8979    

DOI:10.1063/1.351982

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Photoion and photoelectron yields were measured for poly(methylmethacrylate) in the photon energy region of 8–40 eV using synchrotron radiation. Further, the valence‐band structure was investigated with ultraviolet photoelectron spectra and valence effective Hamiltonian calculations. A significant difference was observed between the photon energy dependencies of photoion and photoelectron yields. The threshold energy for photoion emission was found to be 10.5 eV, while that for photoelectron emission was 8.5 eV, indicating holes created near the valence‐band top do not contribute to the ion emission. At the higher‐energy region, the ion emission efficiency was found to be enhanced in the photon energy region of 17–28 eV. The difference between the threshold energies of photoion and photoelectron emission and the enhancement of the photoion emission are discussed in conjunction with the valence‐band structure.

ISSN:0021-8979    

DOI:10.1063/1.351983

出版商:AIP    

年代:1992

数据来源: AIP