摘要:

The existence of an outer cracked layer and an inner more structured porous layer has been observed in electrochemically obtained porous silicon when drying procedures are carried out. The changes in the charge transferred to the porous structure during voltammetric oxidation, the interference fringes obtained by Fourier‐transform infrared spectroscopic measurements, and scanning electron microscopy micrographs confirm the existence of this double layer. Also, drying procedures and voltammetric oxidations drastically affect the intensity and wavelength of the peak maximum in the photoluminescence spectrum. The evolution of the luminescent properties is explained by the introduction of nonradiative recombination centers. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361268

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Mn‐activated Zn2SiO4and Ce‐activated Y2SiO5multilayer thin film electroluminescent (EL) devices were prepared by rf magnetron sputtering. The EL response of the devices under different voltages, frequencies, and pulse widths, as well as the transferred charge and decay characteristics were studied. The EL device using Zn2SiO4:Mn as the phosphor layer is shown to achieve a brightness of over 200 cd/m2at 400 Hz and a field of 3×106V/cm (twice the threshold field) and a maximum efficiency of 0.78 lm/W, with a decay time of 0.6 ms. The main characteristics of the oxide phosphors include (a) strong trailing edge excitation in nonsymmetrical EL devices, (b) a narrow transferred charge loop, and (c) a time response sensitive to device structures. Compared with the nonsymmetrical structure, the more symmetrical double‐insulated structure is shown to increase the efficiency of the EL device by generating strong EL excitation from both positive and negative voltage pulses. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361269

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The longitudinal (LO) and transverse (TO)A1vibrational modes have been measured between 30 and 1200 cm−1as a function of temperature (30–1240 K) for both KTiOPO4(KTP) and KTiOAsO4(KTA). KTP and KTA exhibit an obviously different Raman spectra in the frequency region 400–650 cm−1(with respect to KTA). This middle‐frequency difference is attributed to the substitution ions in XO4group (X=P or As) modifing the force constant of crystal. The relative intensities of the low‐frequency bands increase dramatically with increasing temperature due to high mobility of K+ion. There is no typical soft‐mode like behavior in the measured frequency range. A higher symmetric structure taking place aboveTchas been confirmed by the disappearance of theA1g(LO) stretching modes of TiO6group. Comparison of each frequency belonging to the symmetryA1,A2,B1, andB2measured along the [110] phonon direction shows complex difference. The vibrational frequencies of various symmetries were also obtained. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361270

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Dielectric properties of potassium titanyl phosphate have been investigated as a function of thickness and frequency, as well as annealing treatment under various atmospheres. The low frequency dielectric constant of KTP crystals is shown to depend upon the sample thickness, and this feature is attributed to the existence of surface layers. The frequency‐dependent dielectric response of KTP exhibits a non‐Debye type relaxation, with a distribution of relaxation times. The dielectric behavior of KTP samples annealed in various atmospheres shows that the low frequency dielectric constant is influenced by the contribution from the space charge layers. Prolonged annealing of the samples leads to a surface degradation, resulting in the formation of a surface layer of lower dielectric constant. This surface degradation is least when annealed in the presence of dry oxygen. From the analysis of the dielectric data using complex electric modulus, &agr;mhas been evaluated for the virgin and annealed samples. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361217

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Passivation of point and extended defects in GaSb has been observed as a result of hydrogenated amorphous silicon (a‐Si:H) treatment by the glow discharge technique. Cathodoluminescence (CL) images recorded at various depths in the samples clearly show passivation of defects on the surface as well as in the bulk region. The passivation of various recombination centers in the bulk is attributed to the formation of hydrogen‐impurity complexes by diffusion of hydrogen ions from the plasma.a‐Si:H acts as a protective cap layer and prevents surface degradation which is usually encountered by bare exposure to hydrogen plasma. An enhancement in luminescence intensity up to 20 times is seen due to the passivation of nonradiative recombination centers. The passivation efficiency is found to improve with an increase ina‐Si:H deposition temperature. The relative passivation efficiency of donors and acceptors by hydrogen in undoped and Te‐compensatedp‐GaSb has been evaluated by CL and by the temperature dependence of photoluminescence intensities. Most notably, effective passivation of minority dopants in tellurium compensatedp‐GaSb is evidenced for the first time. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361220

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A study was made on the characteristics of cathodoluminescence (CL) from Si crystals with various configurations of dislocations. D3 and D4 were observed along slip lines, while D1 and D2 were found to be strong in the region where plural slip lines intersect each other. It was shown that not only Lomer–Cottrell dislocations but also jogs act as recombination centers for D1 and D2 luminescence. The spatial distributions of D1 and D2 luminescence were observed to be similar to each other, this was also true of D3 and D4. The effect of hydrogenation on CL distribution was also investigated. Contrary to the reports of other groups, no evidence was obtained on the enhancement of D line luminescence due to metal contamination. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361271

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Band‐edge‐related photoluminescence in Yb‐doped InP was investigated by solving rate equations. For InP:Yb, two characteristic properties have been observed in the band‐edge‐related luminescence. One is that the decay curve of the band‐edge‐related luminescence has a slowly decaying component above about 100 K, which has not been observed in undoped InP. The other is that the luminesce intensity shows an increase at around 120 K, although that for undoped InP monotonically decreases as temperature increases. These two properties were investigated based on a proposed model of energy transfer between the Yb 4fshell and the InP–host electrical state. In the model, it is assumed that a nonradiative multiphonon transition process assists the energy transfer. We have shown, in a previous article, that the temperature dependence of the decay time and of the intensity of the Yb 4fshell luminescence can be explained by using this assumption. In this article, we calculated the band‐edge‐related luminescence properties under the same assumption. Good agreement was obtained between the calculated and experimental results. Thus, the experimentally observed characteristic properties in the band‐edge‐related luminescence are explained by the energy backtransfer from the excited Yb 4fshell to the host electronic state. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361272

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The planar radius and the binding energy of excitons in extremely shallow quantum well (ESQW) structures are calculated theoretically. As the strength of an applied electric field increases, the exciton planar radius increases and the binding energy decreases rapidly compared with a conventional quantum well, which explains the rapid peak quench in ESQW structures. We also calculate the energy difference between heavy hole and light hole exciton transitions in quantum wells with various barrier heights. Due to the small energy difference in ESQW structures, the light hole peak is not clearly resolved from heavy hole peak by room‐temperature photocurrent experiments. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361224

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The optical absorptions of anodically etchedp+andn+porous silicon (PS) films were investigated by photothermal deflection spectroscopy. Si–H stretching overtones and combination bands of Si–F and Si–H were observed. The defect model in hydrogenated amorphous silicon was used to explain the Urbach edge and the subgap absorptions of PS. The dangling bond defect densities in PS were estimated. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361216

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The anisotropy of the thermal oxidation of 6H‐SiC has been investigated. Spheres of Acheson and modified Lely single crystals were prepared and subsequently oxidized under wet oxidation conditions. Afterwards the spheres showed an impressive image of interference colors in different crystal orientations due to different oxide thicknesses. The star‐shaped structure on the (0001) Si face and the regular structure in the plane perpendicular to thecaxis with six maxima and six minima is remarkable. The orientation of one maximum of oxide thickness could be assigned from Laue diffraction patterns to the (11¯00) and the orientation of one minimum of oxide thickness to the (112¯0) orientation. The oxide thicknesses were determined by Rutherford backscattering spectrometry and subsequently fitting of the measured Rutherford backscattering spectra by a spectrometry simulation program on various points on the spheres. The oxide thickness was determined as a function of the azimuth angle of the sphere. Different behavior at the interface SiC/SiO2for the (0001) Si face and the (0001¯) C face was observed and is discussed. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361225

出版商:AIP    

年代:1996

数据来源: AIP