摘要:

Modulation of midinfrared beam by photoinduced intersubband absorption in undoped Si/SiGe quantum wells is investigated at normal incidence. Optical pumping of interband transitions is used to photocreate carriers in the wells. The modulated transmission of the sample is measured by Fourier transform spectroscopy. Resonant dispersion associated with intersubband transitions as well as interference effects in the quantum well stack are clearly evidenced. It is shown that the phase modulation due to refractive index variations may compensate for amplitude modulation due to absorption. Measurements are well fitted by a phenomenological model. It is also shown that the modulation depth and the wavelength modulation profile both depend on the interband excitation wavelength. This result is attributed to the different nature of photoinduced transitions according to the excitation wavelength. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115247

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have investigated photoexcited carrier lifetimes in arsenic‐ion‐implanted semi‐insulating GaAs by time‐resolved reflectivity measurements. Subpicosecond carrier lifetimes (220 to 550 fs) which do not exhibit apparent dosage dependence for samples bombarded with 200 keV arsenic ions at increasing dosages in the range of 1012and 1016ions/cm2are reported. The shortest carrier lifetime was observed for the sample irradiated at 1013ions/cm−2. These are the shortest lifetimes ever observed for ion‐damaged GaAs and comparable to those of low‐temperature molecular beam epitaxially grown GaAs, which is also nonstoichiometric with excess‐arsenic‐related, deep‐level defects. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115248

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The effect of hydrogen dilution on the light degradation behavior of amorphous silicon (a‐Si:H)p‐i‐nsolar cells fabricated by mercury‐sensitized photochemical vapor deposition has been systematically investigated. In the case of solar cells with nop/ibuffer layer, the open‐circuit voltage (Voc) of the cells with theilayer prepared by H2‐diluted SiH4was found to increase with the light‐soaking time, while theVocof the cell withilayer prepared from pure SiH4decreased. Moreover, the single junction solar cell with theVocof 1.001 V and fill factor of 0.72 has been achieved by optimizing H2dilution ratio inilayer and employing the wide band gappand buffer layer. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115249

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The photoluminescence (PL) spectra of C60molecules embedded in porous Si through both physical deposition and chemical coupling were measured. In addition to the PL peak of porous Si, a peak at 730 nm caused by perfect C60molecules and other peaks at 620 and 630 nm caused by imperfect C60molecules were observed. The peak at 620 nm measured in the sample with physically deposited C60is induced by C60adsorbed on the Si atoms of the pore wall, while the peak at 630 nm measured in the sample with chemically coupled C60molecules is caused by the coupled C60molecules. At room temperature, the PL intensity of C60embedded in the porous Si is obviously enhanced, and the transfer of carriers from porous Si grains into adjacent C60is considered to be responsible for the PL enhancement. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115250

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Anisotropic materials with layered structure, like MoS2and WSe2, play an important role in a number of technologies. Some of these applications (lubrication, photovoltaics) require polycrystalline films oriented with theircaxis perpendicular to the substrate surface (type‐II texture), which is the thermodynamically favorable texture. However, films with the substrate ∥c(type‐I texture) are usually obtained. We report that an ultrathin (<10 nm) metal‐chalcogenide interlayer eutectics, like Ni3Se2, SnSe<thin>2, or InSe disentangle the growth mode of the film from the underlying amorphous substrate, and hence, WSe2films with a perfect type‐II texture and crystallites at least a few mm2large are obtained at temperatures as low as 700 °C (van der Waals rheotaxy–vdWR). The mechanism for this growth mode is proposed. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115251

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The radiation effect on then‐channel polycrystalline silicon (polysilicon) thin‐film transistors has been investigated. It is found that for an unhydrogenated device, the irradiation of Co60with a total dose of 1 Mrads caused a negative threshold‐voltage (Vth) shift and a slight subthreshold‐swing (S) degradation, while for a hydrogenatedn‐channel device, the same irradiation results in a positiveVthshift and a seriousSdegradation. It is also found that the radiation hardness of the hydrogenated devices can be improved somewhat by a simple irradiation‐then‐hydrogenation treatment. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115252

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present quantum mechanical calculations of electron capture rates in cylindrical quantum wires via polar‐optical phonon scattering. The capture rate dependence on quantum wire radius and lattice temperature is investigated. An oscillatory behavior of the electron capture rate is observed as a function of the quantum wire radius at the temperatures considered in this study (20–300 K). However, the amplitude of these oscillations decreases significantly at large wire radii and high lattice temperatures. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115253

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Nanometer‐sized GaAs particles embedded in SiO2were prepared by a digital rf‐sputtering method, where GaAs and SiO2targets were alternately sputtered in an Ar atmosphere. The GaAs deposition time was kept shorter than the time required to form a continuous layer. Transmission electron microscopy observations showed that the sizes of the GaAs particles can be controlled from 2 to 8 nm by changing the sputtering cycle time of the GaAs target. In spite of their small size, the GaAs particles have crystallinity similar to the target material without substrate heating or postannealing. The optical absorption spectra of the GaAs particles show a blue shift as large as 1.6 eV, corresponding to strong quantum confinement of electrons and holes. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115254

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The current‐voltage characteristic of a semiinsulating, monocrystalline ZnS film grown by metalorganic vapor‐phase epitaxy is reported. High‐field conduction is found to occur in the same field range (1.0–1.5 MV/cm) as in highly defected, electroluminescent material. It is concluded that the conduction mechanism underlying the operation of ZnS‐based electroluminescent devices is bulk controlled. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115255

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The origin of stress‐induced leakage current in ultrathin SiO2has been quantitatively investigated on the basis of the experimental results on temperature dependence of stress‐induced leakage current. We found that stress‐induced leakage current is dependent on stressing temperature, and that it is independent of measurement temperature. It has been quantitatively demonstrated for the first time that the activation energy of the appearance of stress‐induced leakage current agrees well with that of electron trap generation so far reported. It is discussed quantitatively that stress‐induced leakage current and electron trap generation have a common origin. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115256

出版商:AIP    

年代:1995

数据来源: AIP