摘要:

Poly(p-phenylenevinylene) and its derivatives (DP-PPV and labeled R-7) were carefully studied using x-ray photoelectron spectroscopy. The C1speaks taken from spin-coated thin films of these materials were fitted with the consideration of the bonding state differences(–C=CHandC=C–, etc). The intensity of these C1speaks agrees well with the value estimated from the bonding state consideration. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366362

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have investigated steady-state and transient electrical properties of undoped polycrystalline diamond thin films deposited using hot filament chemical vapor deposition on (100)-orientedn-type andp-type silicon substrates. The capacitance-voltage characteristics are strongly influenced by slow traps located close to the interface between the diamond layer and the silicon substrate. When interpreting data one has to consider that the traps are not in thermal equilibrium during measurements. The steady-state current through the diamond film has the same behavior for films deposited on bothn-Si andp-Si. Its temperature and field dependency can be interpreted in terms of Poole–Frenkel transport involving ionized sites with overlapping potentials in the diamond film. Electrically excited current transients decay with time according to a power law. The kinetics depend only weakly on temperature. Further, the transients contain very long time scales and show much similarity to earlier reported optically excited ones. The temperature and voltage dependency of the transient current magnitude are similar to the ones of the steady-state current for a nonzero field across the diamond layer during the transient. It is possible to qualitatively account for the steady-state and transient transport within the framework of the same basic model assuming that the traps involved in the transport have a certain spatial and energy distribution. From an application point of view the leakage currents in the diamond film are of acceptable magnitude for many diamond based silicon-on-insulator applications intended for operation at moderate temperatures and voltages. Finally, the films also show promising behavior with respect to material reliability; from the electrical measurements no sign of degradation of the diamond films due to long term current stress can be seen. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366363

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have investigated the temperature dependencies of charge carrier densities and Hall mobilities in tensile strainedSi1−yCyand in compressively strainedSi1−x−yGexCylayers. In both cases, the measured charge carrier densities at room temperature are not affected substantially by the addition of a small concentration of carbon (<1&percent;) under identical growth conditions and dopant fluxes. The measured Hall mobilities monotonically decrease with increasing carbon content for electrons inSi1−yCy,and for holes inSi1−x−yGexCy,respectively. Our results indicate that electrically active defects are formed with the addition of carbon. These defects are presumably connected with carbon/Si interstitials or other C-related complexes. It seems to be difficult to attribute the formation of those electrically active defects solely to contaminations originating from the used carbon evaporation source. We observed that donor- and acceptor-like defects are formed inSi1−yCyas well as inSi1−x−yGexCylayers with roughly a constant ratio, independent of source temperature. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366364

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Temperature dependent Hall effect measurements were made on Na-contaminated and uncontaminated epitaxialp-typeCuIn1−xGaxSe2films. Na was introduced by diffusion into as-deposited samples using both NaOH andNa2Seas sources. Na concentrations were measured using secondary ion mass spectroscopy by comparison to an implanted standard. Films contaminated with Na from either source were found to have much lower compensating donor densities than as-deposited films. Oxygen and other impurities were not found to be necessary to produce this effect although some changes with Se content were observed. These were independent of the Na effect. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366365

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The capture and emission dynamics of deep levels inGaAs/Ga1−xAlxAsmultiple quantum well structures are investigated by using the photoinduced transient spectroscopy technique. In nominally undoped samples three trapping levels with activation energies in the range between 0.4 and 0.8 eV are observed. These are compared with the observations based on other conventional techniques. Large capture cross sections associated with the trapping centers implies that the presence of these can be detrimental for the high speed operation of optoelectronic devices based onGaAs/Ga1−xAlxAsquantum well structures. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366366

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Ultrashallowp+njunctions have been formed in silicon by low energy (5.5 keV)Ga+implantation inton-type substrates. This avoids the use implantation of molecular species such asBF2+or preamorphization withGe+orSi+,which degrade the integrity ofp+njunctions in metastably strainedSixGe1−xlayers. High resolution secondary ion mass spectroscopy measurements indicate an implant peak at less than 10 nm, except for postanneal temperatures above 800 °C, for which severe loss of profile control was observed. Electrical characteristics of the implanted junctions were determined from diode current–voltage measurements and Hall data. At low anneal temperatures, these showed good rectification behavior, with an ideality factor of 1.1±0.1 and a reverse bias leakage of≈3 &mgr;A cm−2in a relatively large junction area of5×10−2 cm2.The electrical properties of thep+njunctions were found to be sensitive to implant dose, improving with increasing dose. At 580 °C, implant doses were achieved that were completely activated at levels above previously published Ga equilibrium solubility data. For temperatures of 800 °C, reverse annealing occurred, observed as a reduction in carrier concentration with increasing anneal time and severe profile broadening. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366367

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Nitrogen ions were implanted intoZnSxSe1−xepilayers grown onp-GaAs (100) substrates by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD). Dopant activation and annealing out the implant damage were achieved by a postannealing process in aN2ambient. Schottky structures employing the implantedp-typeZnSxSe1−xwere fabricated and device efficacy was examined by photoluminescence (PL) spectroscopy, current–voltage(I–V),current–voltage temperature(I–V–T),and high frequency capacitance–voltage(C–V)measurements. PL spectra showed a clear donor–acceptor pair (DAP) recombination at an energy of 2.735 and 2.72 eV, in both MBE and MOCVD ZnSSe epilayers, respectively, regardless of the postannealing temperatures. The diode conduction in forward bias proceeds by the combination of thermionic and tunneling emission.C–Vmeasurement proved the maximum doping concentration to be around1017 cm−3after ion implantation. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366368

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The subband dispersion relations have been computed as a function of the surface electron concentration in the accumulation layers ofn-Hg1−xCdxTephotoconductive detectors, while the mobility and concentration for all kinds of carriers in the subband are determined from Shubnikov-de Haas (SdH) oscillation measurements and quantitative mobility spectrum analysis (QMSA). The results show that the QMSA can provide accurate electric parameters for all kinds of carriers in the subband without considering the complex energy band in the semiconductors, while the SdH oscillation can only offer qualitative data because the analysis is based on parabolic energy band approximation. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366369

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The current–voltage characteristics of a Schottky diode are simulated numerically using the thermionic emission-diffusion mechanism and considering a Gaussian distribution of barrier heights, with a linear bias dependence of both the mean and standard deviation. The resulting data are analyzed to get insight into the effects of distribution parameters on the barrier height, activation energy plots and the ideality factor over a temperature range 50–300 K. It is shown that with a Gaussian distribution of the barrier heights the system continues to behave like a single Schottky diode of apparently low zero-bias barrier height and a high ideality factor. Its barrier height decreases, activation energy plot becomes non-linear and ideality factor increases with a decrease in temperature. While the distribution parameters are responsible for the abnormal decrease of barrier height, their bias dependences account for the higher ideality factor at low temperatures. Also, the pivotal role played by series resistance in influencing the linearity of the ln(I)–Vplots of Schottky diodes with a Gaussian distribution of barrier heights is discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366370

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The thermal stability of Ti/Pt/Au Schottky gates on high-low doped GaAs metal–semiconductor field-effect transistors (MESFETs) was investigated in the temperature range of 300–500 °C, using current–voltage and capacitance–voltage measurements and cross-sectional transmission electron microscopy with energy dispersive x-ray spectroscopy. At annealing temperatures>350 °C,the interfacial reactions cause the formation of a layered structure of Ti/Ti–Ga/Ti–As/GaAs. The depth distribution of electron concentration moves toward the Ti/GaAs interface as the annealing temperature increases. This is due to the growth of Ti–As, followed by the reduction of the channel thickness. The activation energy for the growth of Ti–As is determined to be 1.74 eV. The electron concentration in the channel layer decreases with the increase of the annealing temperature. This is due to the out-diffusion of Ga to the Ti film, resulting in the production of acceptor-type Ga vacancies and thereby the decrease of electron concentration in the channel. The activation energy for the reduction of electron concentration, equal to the formation energy of the acceptor-type Ga vacancies, is determined to be 1.42 eV. This is closed to the activation energy of 1.3 eV for the device failure obtained at annealing temperatures ranged from 300 to 350 °C. From these observations, it is proposed that the thermal degradation of GaAs MESFETs at temperatures<350 °C,mainly proceeds by the electron compensation with acceptor-type Ga vacancies in the channel, whereas it occurs by the growth of Ti–As below the original Ti/GaAs interface at temperatures>350 °C.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366371

出版商:AIP    

年代:1997

数据来源: AIP