摘要:

Hydrogenated amorphous-silicon–nitride thin-film diode (TFD) switches have been shown to degrade electrically at both the cathode (electron injection contact) and anode (noninjection contact) due, respectively, to electron–hole recombination and hot-electron-induced-state creation mechanisms. An antiparallel configuration of two asymmetric TFDs provides an elegant method to minimize the cathodic degradation and avoid the consequences of anodic defect state creation. In this way, extremely stable TFDs may be prepared. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120654

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report on excitonic transitions observed at room temperature in multilayers of(GaAs)1−x(Ge2)x/GaAsgrown by magnetron sputtering. We attribute the observation of the exciton absorption at room temperature to confinement effects on the bound electron–hole pairs inside the Ge-rich layers of the(GaAs)1−x(Ge2)xalloys. From secondary ions mass spectroscopy these layers are measured to be 50, 33, and 30 nm in full width at half maximum (FWHM), for three different samples. These layers alternate with(GaAs)1−x(Ge2)xalloy layers of very low Ge concentration that can be considered of plain GaAs,∼360 nmin thickness for two samples and 240 nm for a third one. The observed transition energies of the exciton are very close to≈1 eVboth at 300 and 4 K. A calculation of exciton energy-level spacing and transition probabilities provides acceptable values for the exciton transition energies observed, considering a triangular quantum well as an approximation to the Ge profile in the confinement layers. The observed excitonic FWHM remain nearly constant at all temperatures examined (300–4 K). ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120655

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have observed differential reflection dynamics inIn0.518Ga0.492As/InPmultiple quantum wells, using the pump–probe technique, and examined the photoluminescence spectra to determine the interface quality for the samples studied. Our results show that the interface quality and well width of the quantum wells (QWs) strongly influence the differential reflection dynamics. The experimental results provide a direct evidence to demonstrate that photoexcited carrier diffusion in cap layer and barriers along the direction perpendicular to sample surface plays a dominant role in determining the differential reflection dynamics of the QWs. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120656

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Enhancement of the photocurrent density generated by internal moving space charge electric fields in semi-insulating GaAs multiple quantum wells is observed when the sample is biased with a high speed, zero-mean square wave electric field which increases the internal space charge electric field strength. Tunability of the space charge field formation time is also demonstrated by adjusting the amplitude of the bias signal. This technique can be used to enhance the sensitivity of optical doppler frequency measurements based on moving space charge field effects in photoconductive semiconductors. Electronic tunability of the space charge field formation time also adds versatility in optical power spectrum analysis applications. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120657

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

While sensitization of the photoconductivity, i.e., the increase of the majority carrier lifetime by the addition of recombination centers, is known for many years, there was no evidence or suggestion for the corresponding sensitization of the minority carrier lifetime. In this letter, we present experimental evidence for the existence of such an effect in device quality undoped hydrogenated amorphous silicon films. We propose possible scenarios that can yield the observed effect and mention the possible benefits of the minority carrier sensitization for the improvement of bipolar optoelectronic devices made of this material. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120658

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A boron-doped hydrogenated amorphous diamondlike carbon(a-DLC:H)was prepared using a mercury-sensitized photochemical vapor deposition (photo-CVD) method. The source gases wereB2H6andC2H4.By increasing the boron doping ratio(B2H6/C2H4)from 0 to 12 000 ppm, the dark conductivity increased from∼10−9to∼10−7 S/cm.A boron-dopeda-DLC:Hwith an energy band gap of 3.8 eV and a dark conductivity of1.3×10−8 S/cmwas obtained at a doping ratio of 3600 ppm. By using this film, amorphous silicon(a-Si)solar cells with a novelp-a-DLC:H/p-a-SiCdoublep-layer structure were fabricated using the photo-CVD method and the cell photovoltaic characteristics were investigated as a function ofa-DLC:Hlayer thickness. The open circuit voltage increased from 0.766 V for the conventional cell with a 40-Å-thickp-a-SiCto 0.865 V for the cell with ap-a-DLC:H(15 Å)/p-a-SiC(40 Å) doublep-layer structure. The thin (<15 Å)p-a-DLC:Hlayer proved to be an excellent hole emitter as a wide band gap window layer. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120659

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Wurtzite GaN films have been grown on (001) Si substrates using&ggr;-Al2O3as an intermediate layer by low pressure(∼76 Torr)metalorganic chemical vapor deposition. Reflection high energy electron diffraction and double crystal x-ray diffraction measurements revealed that the thin&ggr;-Al2O3layer of “compliant” character was an effective intermediate layer for the GaN film grown epitaxially on Si. The narrowest linewidth of the x-ray rocking curve for (0002) diffraction of the 1.3 &mgr;m GaN sample was 54 arcmin. The orientation relationship ofGaN/&ggr;-Al2O3/Siwas (0001) GaN‖(001)&ggr;-Al2O3‖(001)Si, [11–20] GaN‖[110]&ggr;-Al2O3‖[110]Si. The photoluminescence measurement for GaN at room temperature exhibited a near band-edge peak of 365 nm (3.4 eV). ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120660

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We investigated the possibility of reducing the giant flux creep in high-temperature superconductors by temporarily increasing the temperatureTabove the operating temperatureT0,afterthe critical state is created atT0.ThisTincrease leads to asupercriticalstate which decays rapidly so that, whenTis decreased back toT0, the superconductor is in the subcritical state. We have found that both the maximum persistent current and the relaxation rate are hysteretic and differ substantially from the corresponding quantities measured after flux annealing. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120661

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The dc-superconducting quantum interference device (SQUID) is a low-noise converter from magnetic flux to voltage which can have, in principle, an energy sensitivity near the quantum limit ofℏ/2.A critical parameter for the ideal performance is the device inductance, which must be kept as small as possible. Minimizing the SQUID inductance, however, is a major concern for a practical device; this requirement implies a small SQUID ring and hence magnetic coupling with an external signal is more difficult to achieve. Here we present an original scheme (called multiwasher) to circumvent this problem, and its implementation in an all-refractory thin-film device. Our scheme not only provides good magnetic coupling with a large input coil (0.5 &mgr;H) and very low SQUID inductance, but also shielding from outside uniform fields, such as those generated by ambient disturbances. The measured coupled spectral energy sensitivity in the white region at about 1 kHz is 28ℏ at 4.2 K and 5.5ℏ in a pumped helium bath at 0.9 K. The flux noise spectral density at 0.1 Hz and 0.9 K is&Fgr;n=1×10−6 &Fgr;0/Hz.©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121444

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Spin-valve properties are adversely affected by heat treatments and in order to study this effect, microstructural analyses of Ti/Co/Cu/Co/MnFe/Ti spin-valve films annealed at 225 and at 290 °C have been performed. Whereas the lower temperature tends to optimize the giant magnetoresistance (GMR) ratio, the higher temperature induces a significant decrease in the GMR ratio (from 7.5&percent; to 5.2&percent;). High resolution electron microscopy studies have explained this result as being due to the formation of a TiCo alloy at the Ti/Co interface and to a decrease in the thickness of the sense layer. No significant modification of either the Co/Cu or the Cu/Co interfaces has been observed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120662

出版商:AIP    

年代:1998

数据来源: AIP