摘要:

An analytical theory is presented that leads to the scatter matrix of a sngle electrode for an acoustic surface wave propagating through a periodic array of electrodes on an anisotropic piezoelectric substrate. The scatter matrix elements are obtained analytically as functions of frequency and metallization ratio, considering only the electrical loading by the electrodes; mechanical loading effects are neglected. The results may be used directly in the broad band analysis of surface acoustic wave reflectors and multistrip couplers. Previous works have provided these parameters numerically for electrically shorted and open arrays at stop band frequencies (frequencies where the array period is an integer number of half wavelengths). This work extends the analysis in three ways: (a) the analysis is valid for all frequencies, (b) the external electrical load connected to the electrodes is included as a parameter, and (c) the scatter matrix elements are determined analytically instead of numerically.

ISSN:0021-8979    

DOI:10.1063/1.328315

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A quantitative model has been developed to account for the flow effects in epitaxial autodoping for chemical‐vapor‐deposited films. Analytical expressions are derived for the autodoping variations along and against the direction of flow arising from a diffusion stripe in the substrate. These expressions relate the maximum concentration in the lateral autodoping peak to the distance from the autodoping source and to the carrier gas velocity. Experimental verification of the model is obtained for arsenic autodoping in silicon epitaxial films, which indicates that boundary layer effects are not predominant in the autodoping phenomenon. The analysis also yields a value of 2.5 cm2/sec for the arsenic vapor diffusivity in hydrogen at 1150 °C.

ISSN:0021-8979    

DOI:10.1063/1.328316

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The high electron injection phenomenon of Si‐rich SiO2films deposited on top of SiO2can be used for novel charge trapping studies of sites normally present or purposely introduced in the SiO2. From the position and extent of current ledges observed in dark current as a function of ramped gate voltage, the capture cross section and total number of traps can be determined. Using these measurements with capacitance as a function of gate voltage, the trap distribution centroid and number of trapped charges can also be found. Several experimental examples are given including trapping in thermal SiO2, in chemically vapor deposited (CVD) SiO2, and on W, less than a monolayer thick, sandwiched between thermal and CVD SiO2. These stepped insulator metal‐insulator‐silicon (SI‐MIS) rampI‐Vresults for the trapping parameters are shown to be in good agreement with those determined using the conventional photoI‐Vand avalanche injection with flat‐band voltage tracking techniques. A numerical simulation of the rampI‐Vmeasurements, assuming electric field‐enhanced Fowler‐Nordheim tunneling at the Si‐rich‐SiO2–SiO2interface, is described and is shown to give good agreement with the experimental data. These techniques for SI‐MIS structures are faster and easier, although less accurate than the conventional techniques.

ISSN:0021-8979    

DOI:10.1063/1.328317

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A sharp line transition at 1.51385 eV has been observed in the photoluminescence spectra of an epitaxially grown crystal of GaAs. A Si3N4cap was applied by plasma deposition and the crystal was then annealed at 850 °C for 15 min. The sharp emission line was observed after annealing. This transition was analyzed in perturbing magnetic and strain fields and is shown to result from a donor‐acceptor‐type complex. Three additional sharp line transitions are reported and the behavior of all of these transitions is compared with the behavior of similar transitions reported in the literature. Models for the complexes involved are re‐examined and components of the complexes are suggested. All of the sharp line transitions were introduced in the growing process with the exception of the 1.51385‐eV line which was introduced in the capping and annealing process.

ISSN:0021-8979    

DOI:10.1063/1.328318

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

We present a general model of the frequency dependence of conductance and capacitance ina‐Si:H Schottky diodes. In order to circumvent several questionable assumptions required in the analysis of capacitance voltage characteristics, the frequency dependence of sputtereda‐Si:H devices is measured with no applied dc voltage. We obtain independent, consistent values of the depletion width and of the density of states at the Fermi level and below from both conductance and capacitance at both low and high modulation frequencies. We show that the linear frequency dependence of conductance cannot be attributed to hopping conductance, but rather to the interaction of gap states with free carriers. Our study shows that the interaction kinetics of the states around the Fermi level with the conduction‐band carriers is so fast that the response of the diode is limited by the band transport of these carriers, which rapidly thermalize and distribute themselves through the continuum of states from the conduction band to the Fermi level.

ISSN:0021-8979    

DOI:10.1063/1.328319

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The effect of nonparabolicity on the transverse magnetoresistance of degenerate piezoelectric semiconductors in strong dc magnetic fields has been studied for the case where acoustic phonons are the dominant scattering mechanism. The calculation has been performed taking into account the inelasticities in the electron‐phonon scattering due to the finite energy of phonons involved. Results show that the transverse magnetoresistance due to the piezoelectric coupling for the nonparabolic band structure is enhanced much more considerably than that for the parabolic band structure. From our numerical results for the nonparabolic band structure, it can be seen that the piezoelectric coupling plays the same important role for the transverse magnetoresistance as the deformation‐potential coupling. We also found that the transverse magnetoresistance for both parabolic and nonparabolic band structures oscillates with the dc magnetic field owing to the degeneracy of the electron gas.

ISSN:0021-8979    

DOI:10.1063/1.328320

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The conversion of semi‐insulating GaAs toptype as a result of heat treatment in H2was studied by photoluminescence (PL), secondary‐ion mass spectrometry (SIMS), and transport measurements. The SIMS measurements resulted in the direct chemical identification of Mn near the heated surface. The correlation of the SIMS profiles with the results of PL and transport measurements indicated that Mn acceptors are responsible for the type conversion, and that substantial concentrations of Mn(?1017/cm3) are found in thin (1–3 &mgr;m) layers near the surface. The results of studies of samples heated under several different conditions showed that the Mn layers were not introduced by contamination from external sources during heat treatment, but were probably due to the presence of a bulk Mn concentration (<3×1015/cm3): during heat treatment the Mn diffuses to the surface, probably assisted by the in diffusion of Ga vacancies, as suggested by Zucca. Photoluminescence profiling measurements and the correlation between the SIMS and PL results indicate that the 1.41‐eV PL band that is associated with the type‐converted surface is due to recombination at a Mn acceptor on a Ga site, and not at a next‐nearest‐neighbor arsenic vacancy‐amphoteric acceptor complex.

ISSN:0021-8979    

DOI:10.1063/1.328321

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Measurements of space‐charge‐limited currents (SCLC) and thermally stimulated currents (TSC) were done in naphthalene single crystals grown from the melt and also from solution. Crystals grown from the melt were irradiated with x rays to a dose that ranged between 8×104and 6×106R. These crystals were also doped with beta naphthol with concentrations that varied from 10−4to 10−2in mole fraction. Melted crystals showed a trap level at 0.71 eV using SCLC and 0.79 eV using TSC, whereas solution crystals showed 0.43 eV using SCLC and 0.78 eV using TSC. Irradiated samples showed a trap level at 0.50 eV. In the case of doped samples the impurities originate a trap level at a depth of 0.53 eV that was possible to predict theoretically. Results showed that care must be exercised to obtain a valid comparison between the SCLC and TSC measurements and also that trapping of charge carriers is greatly influenced by the conditions under which the crystals were grown.

ISSN:0021-8979    

DOI:10.1063/1.328322

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The radiation‐induced conductivity (RIC) of 2.5×10−3‐cm‐thick Teflon was measured using partially penetrating electrons with an energy of 40 keV. The behavior of the external currents generated during irradiation is expressed by a ’’generalized box model.’’ We explain, with this model, the experimentally observed buildup and decay of the RIC by using a time‐dependent conductivity &sgr;(t)=&sgr;0(1−et/&tgr;s), where &sgr;0is the steady‐state conductivity and &tgr;sis the time constant of the RIC buildup. The time sequence in which voltage and irradiation are applied is found to give significantly different time effects; for irradiation first, the induced conductivity reaches a final value when the voltage is applied, while with voltage first, the conductivity increases with time after the radiation is turned on. Measurements are complex because the nonirradiated region of the foil is entirely blocking for electrons while it allows transport of holes. The peak value of the induced current, and thus of the induced conductivity, increases proportional to ‖I0‖0.79, while the initial slope of the current versus time is proportional to the electron beam currentI0.

ISSN:0021-8979    

DOI:10.1063/1.328323

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Transport properties of AlxGa1−xAs layers having AlAs mole fractions between 0.17 and 0.375 and grown by molecular beam epitaxy were investigated. The Al cell temperature was kept at 1075 °C while the Ga cell temperature was changed between 910 and 950 °C to obtain the aforementioned AlAs mole fractions. The donor levels of Sn in AlxGa1−xAs obtained from the temperature dependence of the net donor concentration are below 3, 30, and 40 meV forx=0.17,x=0.29, andx=0.375, respectively. Al0.22Ga0.78As layers having a net electron concentration of about 1.7×1018cm−3and grown at 630 °C exhibited a mobility of 868 and 1095 cm2/V sec at 300 and 78 °K, respectively. The mobility was found to be strongly dependent on the substrate temperature during the growth. The lower substrate temperatures resulted in lower electron mobility.

ISSN:0021-8979    

DOI:10.1063/1.328324

出版商:AIP    

年代:1980

数据来源: AIP