摘要:

Using an atomic force microscope, we studied various InAs-on-AlSb interface structures grown by molecular beam epitaxy. We found marked differences between the effects of the two interface bond configurations—InSb-like and AlAs-like—on the morphology of the subsequent InAs layer. In general, InSb-like interfaces lead to a much smoother InAs overgrown layer with clearly resolvable monolayer terraces. AlAs-like interfaces, on the other hand, lead to increasingly rougher InAs growth with longer As exposure. Previous studies have demonstrated a strong correlation between the interface configuration and the electron mobility in the InAs quantum well. The morphology and transport results we obtained indicate one reason for the influence of the interface configuration—a rough InAs layer. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366354

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Strontium barium niobate waveguiding thin films were prepared by pulsed laser deposition. The relationship between the film structure and the deposition temperature were analyzed by x-ray diffraction and atomic force microscopy. Waveguiding properties such as refractive index and mode dispersion were examined and a dispersion relation was obtained for the (001)-oriented films. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366355

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The amorphous carbon nitride films were produced using electron cyclotron resonance nitrogen plasma with various mixtures ofN2andCH4gases. The dependence of film structures on the nitrogen incorporation and the structural modifications of the film due to ultraviolet (UV) light irradiation were investigated using infrared and UV-VIS spectroscopy. It is found that UV irradiation results in the decrease of CH bonding, increase of CC and CN double bonding in the film and increase of the optical band gap of the film. It appears that both bond removal and reordering have taken place as a result of UV irradiation. The structural modifications due to nitrogen incorporation and UV light irradiation are explained by a cluster model. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366356

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

To clarify the structure of ultrathin silicon oxide gate films less than about 5 nm thick, densities of the films grown on Si(100) at 800–950 °C by the recently proposed rigorous ultradry oxidation process were determined by charged-particle activation analysis. The density curve plotted as a function of oxidation temperature shows a peak, i.e., the density of the 850 °C grown films is largest of all, about2.38 Mg/m3.Interestingly, a similar relationship is confirmed in the time-dependent dielectric breakdown lifetime characteristic curve, which is the most fundamental index of reliability for the oxide. This suggests that the reliability is closely related to the density. That is, since the density reflects the atomic arrangement of the films, the lifetime enhancement near the same oxidation temperature is possibly caused by changes in the films’ microscopic structure. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366357

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The effects of structural and chemical disorder on electronic and optical properties of InGaAsP quaternary alloy are studied on the basis of a modified virtual crystal approximation calculated within a simple tight-bindingsp3s*theory, which incorporates compositional disorder as an effective potential. Using a minimal set of fitting parameters, we show that such an approach provides analytical results for calculating energy gaps and bowing parameters. We show that the calculated bowing parameter agrees reasonably well with experimental data. The essential features of structure and disorder-induced changes in electronic and optical structure are exhibited in thesp3s*results by two characterization parameters: the subband energy spacings, and the density of states. The changes in each of them are found to depend on the interrelated trends of structure and disorder effects. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366358

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Dimethylzinc (DMZn) was used as ap-type dopant in GaAs grown by low pressure metalorganic vapor phase epitaxy using trimethylgallium and arsine(AsH3)as source materials. The hole carrier concentrations and zinc (Zn) incorporation efficiency are studied by using the Hall effect, electrochemical capacitance voltage profiler and photoluminescence (PL) spectroscopy. The influence of growth parameters such as DMZn mole fraction, growth temperature, andAsH3mole fraction on the Zn incorporation have been studied. The hole concentration increases with increasing DMZn andAsH3mole fraction and decreases with increasing growth temperature. This can be explained by vacancy control model. The PL experiments were carried out as a function of hole concentration(1017–1.5×1020 cm−3).The main peak shifted to lower energy and the full width at half maximum (FWHM) increases with increasing hole concentrations. We have obtained an empirical relation for FWHM of PL,&Dgr;E(p)(eV)=1.15×10−8p1/3.We also obtained an empirical relation for the band gap shrinkage,&Dgr;Egin Zn doped GaAs as a function of hole concentration. The value of&Dgr;Eg(eV)=−2.75×10−8p1/3,indicates a significant band gap shrinkage at high doping levels. These relations are considered to provide a useful tool to determine the hole concentration in Zn doped GaAs by low temperature PL measurement. The hole concentration increases with increasingAsH3mole fraction and the main peak is shifted to a lower energy side. This can be explained also by the vacancy control model. As the hole concentration is increased above3.8×1018 cm−3,a shoulder peak separated from the main peak was observed in the PL spectra and disappears at higher concentrations. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366359

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In traditional band-to-band Auger recombination theory, the low-injection carrier lifetime is an inverse quadratic function of the doping density. However, for doping densities below about 3×1018 cm−3, the low-injection Auger lifetimes measured in the past on silicon were significantly smaller than predicted by this theory. Recently, a new theory has been developed [A. Hangleiter and R. Ha¨cker, Phys. Rev. Lett.65, 215 (1990)] that attributes these deviations to Coulombic interactions between mobile charge carriers. This theory has been supported experimentally to a high degree of accuracy in n-type silicon; however, no satisfactory support for it has been found in p-type silicon for doping densities below 3×1017 cm−3. In this work, we investigate the most recent lifetime measurements of crystalline silicon and support experimentally the Coulomb-enhanced Auger theory in p-type silicon in the doping range down to 1×1016 cm−3. Based on the experimental data, we present an empirical parameterisation of the low-injection Auger lifetime. This parameterisation is valid in n- and p-type silicon with arbitrary doping concentrations and for temperatures between 70 and 400 K. We implement this parameterisation into a numerical device simulator to demonstrate how the new Auger limit influences the open-circuit voltage capability of silicon solar cells. Further, we briefly discuss why the Auger recombination rates are less enhanced under high-injection conditions than under low-injection conditions. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366360

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We studied the process of generation and some properties of shallow donors generated by annealing a hydrogen-doped Czochralski-grown silicon crystal after electron irradiation. Hydrogen was doped by annealing specimens at 1200 °C in hydrogen atmosphere followed by quenching. Specimens were irradiated with 3 MeV electrons. Three kinds of shallow donors, termedD1–D3,were generated and annihilated due to isochronal annealing between 300 and 650 °C as shown by the measurement of optical absorption at 6 K. The generation process ofD1was well described by the first order reaction. The activation energy for the generation ofD1was about 1.8 eV. This agreed well with the migration energy of a vacancy-oxygen pair (VO pair). Hence, it is proposed thatD1is a complex of one VO pair and a hydrogen aggregate. NeutralD1is in a metastable state. The optical threshold energy for the excitation of the neutral charge state ofD1was about 0.36 eV. The energy barrier from the neutral to the stable state ofD1was estimated to be about 0.13 eV. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366361

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The phase stability of the &ggr;-cubicLaSe1.47,LaSe1.48andNdSe1.47compounds with theTh3P4type structure, along with their electrical resistivity, Seebeck coefficient, and Hall effect were measured periodically as the materials were annealed at 800 °C or 1000 °C to determine their potential as thermoelectric materials for long term applications at high temperatures. TheLaSexsamples showed the presence of the ternary oxideLa10Se14O(&bgr;-phase). The content of this phase increased with increasing anneal time, whereas theNdSe1.47samples showed no sign of a ternary oxide second phase. The room temperature electrical resistivity and Seebeck coefficient ofLaSexincreased with increased annealing time, while those ofNdSe1.47decreased. The power factors remained relatively stable with annealing time. The high temperature electrical resistivity ofLaSe1.47andNdSe1.47increased with increasing temperature up to 1000 °C, while the Seebeck coefficient became more negative. The power factor, however, peaks at 800 °C forLaSe1.47and at 500 °C forNdSe1.47.Based on this study we find thatLaSexis not a promising high temperature thermoelectric material due to the formation of the &bgr;-phase, whereas theNdSe1.47which does not form the &bgr;-phase oxide is a potential candidate material. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366293

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this article we report on the electron mobility of a starburst oxadiazole, 1,3,5 -[(4-tert.-butylphenyl)-2-oxadiazolyl] benzene. For direct evidence of the electron transport capability the charge drift mobility and its field dependence have been measured by the time-of-flight technique. The electron mobility showed a square root dependence of the electric field and was somewhat larger than that for PBD. In addition, the oxadiazole compound has been used as the electron transport layer (ETL) in light-emitting diodes (LEDs) together with poly(1,4-phenylene vinylene). The characteristics of these devices are compared to analogous LEDs withAlq3as the ETL. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366396

出版商:AIP    

年代:1997

数据来源: AIP