摘要:

A new structurally defined precursor compound for the low‐temperature metalorganic chemical vapor deposition (MOCVD) of CoAs thin films is reported. The easily accessible 1,3‐bis(tert‐butyl)‐2‐[tetracarbonyl‐cobalt(‐l)]‐1,3,2‐diazarsolidine was decomposed by hot‐wall low pressure CVD. Thin films of cobalt arsenide with retention of the stoichiometry of the precursor (Co:As=1/1) were formed at temperatures as low as 210 °C. Electron micrographs show uniform films, energy dispersive x‐ray spectroscopy, and Auger electron spectroscopy confirm their bulk composition, and powder diffraction patterns and conductivity measurements prove their crystallinity and electrical properties. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115455

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Polycrystalline Cu(In1−xGax)3Se5thin films were prepared by four source evaporation with controlling and shielding of the molecular beams from elemental sources. Ga contentx, can be controlled by deposition times of CuIn3Se5and CuGa3Se5layers, which form Cu(In1−xGax)3Se5films through the interdiffusion. X‐ray diffraction analyses showed that the films withx≲0.5 have an ordered vacancy chalcopyrite and the films withx≳0.5 have a zinc blende structure. The optical band gap of the films linearly increased from 1.23 eV (x=0) to 1.85 eV (x=1) with increasing Ga content. The conductivity of the films was about 10−6/&OHgr; cm and about 10−7/&OHgr; cm under and abovex=0.3, respectively. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115456

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Conductance of ultrathin polycrystalline silicon wire was measured and periodic plateaus, which provide evidence of the Coulomb staircase at room temperature, are observed. This shows that single‐electron charging effects are important to transport in a semiconductor system at room temperature. The very small (∼10‐nm diam) silicon‐grain structure is presumably playing a key role in creating the observed effects. From the temperature dependence, the electron transport is clearly dominated by the thermal emission, whose activation energy is more than 400 meV. This reveals that the treatment beyond well‐established single‐electron tunneling, including thermal‐emission transfer, is essential to understand such high‐temperature charging effects in semiconductor systems. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115457

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Cubic structured CdS, CdSe, and CdTe, II–VI semiconductor nanoparticles have been synthesized using aqueous solution precipitation at room temperature. The ‘‘as‐prepared’’ particles have a size of about 30 A˚. Thermal annealing causes (a) an increase in particle size; (b) a structural transition from the cubic to the bulk, hexagonal structure for CdS and CdSe; and (c) no structural transition for CdTe. The unexpected cubic phase for small particles of CdS and CdSe may be due to either metastability or an equilibrium surface effect. The latter would imply a strong correlation between structure and the size and surface properties, and that there is a minimum size for hexagonal phase stability. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115458

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The subgap optical absorption of GaAs layers grown by low temperature molecular beam epitaxy is measured by photothermal deflection spectroscopy (PDS). The absorption increases as the growth temperature decreases at a fixed wavelength. Defect densities evaluated from the absorption spectra and the known absorption cross sections are between 1018and 1019cm−3. It is shown that complementary PDS phase spectra can be used to separate the absorption of the epitaxial layers from the bulk. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115459

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

AP‐n‐pAlGaAs/InGaAs/GaAs collector‐up heterojunction bipolar transistor (C‐up HBT), grown by three‐stage molecular beam epitaxy, has been fabricated, and its dc and high‐frequency performances have been evaluated. The use of a graded InxGa1−xAs (x=0.0–0.09) is shown to improve the common‐emitter current gain (&bgr;) and to greatly reduce the base transit time (&tgr;b) for theP‐n‐pC‐up HBTs. A maximum current gain (&bgr;) of 150 was measured for a 16×17 &mgr;m2device. From S‐parameter measurements, a best unity‐gain cutoff frequencyfT=43 GHz at a collector current of −10 mA was achieved using a 5×10 &mgr;m2collector area. The results show that theP‐n‐pC‐up HBTs may be useful for future planar integrated circuit applications. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115521

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Results from temperature dependent photoluminescence (PL) transient measurements on metalorganic vapor phase epitaxy grown epitaxial layers of GaN and GaInN are reported. In sufficiently pure GaN layers the free‐exciton PL dominates even at the lowest temperatures (2 K), and the intrinsic excitonic lifetimes can be obtained. We report a value of about 125 ps for the radiative lifetime of the free exciton in GaN at 2 K, as obtained from the PL transients of a 3 &mgr;m buried undoped GaN layer sandwiched between AlN and GaInN. The PL decay time in the ternary alloy GaInN, which is dominated by localized excitons at low temperatures, is much longer, about 500 ps. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115522

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Recent calculations of the electron affinity difference between CdS and CuInSe2indicate that the conduction band (CB) minimum of CuInSe2is below the CB minimum of CdS. As a consequence, a spike occurs in the CB at the CdS/CuInSe2interface. Such a spike is commonly considered as in conflict with good photovoltaic performance of heterojunction solar cells. It is outlined here that the simple assumption of thermionic emission across the junction can explain an unimpeded electron transport in the case of ann+pstructure (n‐type window,p‐type absorber), even when a spike in the CB occurs. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115523

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The effect of GaAs cap layer with different thicknesses in the GaAs/In0.3Ga0.7As/GaAs heterostructure on misfit dislocation is investigated with transmission electron microscopy, and it is found that lines of misfit dislocation break up and move out of the structure when the GaAs cap layer thickness exceeds a certain amount. The breaking up and moving out of misfit dislocations, initially confined in the (001) substrate/InGaAs epilayer interface, occur mainly along the [110] direction on the interface in the structure. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115524

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A pulsed‐current technique was used to measure the extendedI–Vcharacteristics of a wide variety of prototype high‐temperature‐superconductor (HTS) leads. It was found that the average resistivity rises withJ(≳Jc) more gradually than in conventional superconductors—often remaining very small compared to silver, for values ofJ(≫Jc) that are high enough to be practically useful. This observation, combined with the low thermal conductivity (∼50 times smaller than Ag), should extend the utility of HTS leads to the dissipative regime whereJ/Jc≫1. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115525

出版商:AIP    

年代:1995

数据来源: AIP