摘要:

Electrical conductivities(&sgr;dc)of the as-quenchedBi3.5Pb0.5Sr3Ca3Cu4Ox+zAg2O(withz=1,3, 5, and 10 wt &percent;) glassy precursors for highTcsuperconductors are found to be much higher(∼10−5−101 &OHgr;−1cm−1)than those of the correspondingAg2OfreeBi3.5Pb0.5Sr3Ca3Cu4Ox(denoted by BPB) precursor glass(∼10−13−10−6 &OHgr;−1cm−1).This unusually high conductivity is attributed to the increase of carrier concentrations caused by the addition ofAg2O(also observed from the Hall effect measurements). The experimentally observed high values of&sgr;dcdo not follow Mott’s variable range hopping model which is in sharp contrast to the behavior of the corresponding pure BPB and many other conventional transition metal oxide glasses having high resistivities. Moreover, the Seebeck coefficients(S)of these glassy precursors show nonlinear variations (from negative at lower temperature to positive at higher temperature) which cannot be clearly explained by phonon drag or electron-phonon interaction. This behavior ofSwhich is also supported from Hall effect measurement is considered to be due to the nonlinear thermal variations of carrier concentrations (both hole and electron) present in the glassy samples. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365330

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The means by which deep traps in annealed low temperature molecular beam epitaxy grown GaAs are responsible for its remarkable semi-insulating and short lifetime properties has been the subject of much discussion. For example, while low dc bias and high speed phototransient measurements can be explained as consequences of a homogeneous trap distribution in the non-stoichiometric material, experiments demonstrating the presence of electrically active precipitates must be dealt with. The study below, which is numerical, concludes that a consistent argument based on the presence of electrically active precipitates, coupled to a surrounding distribution of traps, will account for much of the observed experimental phenomena. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365331

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

For iron detection in silicon, minority carrier diffusion length measurements are often used. These methods analyze only the bulk properties of the wafer and therefore failed in the case of epitaxial wafers due to the disturbing influence of the highly doped substrate. A technique is presented for the determination of the iron content in epitaxial as well as in polished wafers using generation lifetime measurements on metal-oxide-silicon capacitors. The influence of interstitial iron and iron-boron pairs on generation lifetime was investigated for samples diffused with iron in boron-doped silicon. The difference in reciprocal generation lifetime before and after a thermal anneal of 200 °C for three minutes was calibrated using deep level transient spectroscopy to detect the iron-boron pair concentration. For a typical metal-oxide-silicon capacitor fabrication process this means a detectability limit for iron-boron concentrations of about8×1010 at/cm3.The advantage of this method is that it detects iron in a surface near region in contrast to the often used diffusion length measurements. This gives us the opportunity of controlling the iron content in epitaxial wafers as well as in wafers after an internal gettering process. In addition, the iron-boron pairing reaction was investigated in the temperature range between 21 and 50 °C. The activation energy for this reaction was determined to be 0.70 eV. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365440

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The experimental requirements forlow frequencyelectrical noise measurements of single electron tunneling (SET) semiconductor samples are discussed and a two-channel cross-correlation spectrum analysis method combined with ultralow noise detection is proposed which gives 10 mK noise temperature resolution. We emphasize the effect of the high frequency photon radiation originating from theexternalcircuit which may strongly affect sub-kelvin low frequency noise measurements if not filtered. We quantitatively show that hot photons are important as a mechanism of activation of electron traps for semiconductor SET devices, increasing low frequency1/for telegraphic noise, and as a mechanism to increase the electronic temperature. We describe a new type of cryogenic coaxes whose attenuation drastically thermalizes the photons. As a check, we show for the first time resonant tunneling peak linewidths in the Coulomb blockade regime decreasing with temperature down to≃60mK. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365332

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A theoretical investigation of radiative and nonradiative recombination of excess carriers in a semiconductor quantum well (QW), which takes into account the exciton screening effect, is presented. The analytical formula of photoluminescence (PL) lifetime and efficiency of a QW are obtained. Calculations for the case of GaAs/AlGaAs quantum wells show that the variation of PL lifetime and efficiency with temperature is strongly related to material characteristics as well as the detailed growth techniques. When the ratio of the radiative recombination rate to the nonradiative recombination rate is less than unity, there is no characteristic temperature. In the regime of low excitation intensity, the increase of the majority carrier density is helpful to enhance the formation of the electron-hole pairs into excitons. Under higher excitations, the exciton population factor and the PL efficiency increases with increasing excitation intensity. The exciton screening effect depends, in addition to excitation intensity, upon background carrier density. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365333

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report the observation of deep traps localized near the heterointerface of the InGaP/AlGaAs structure grown by liquid-phase epitaxy. In the case of low-quality InGaP/AlGaAs heterojunctions containing interface traps, the shape of capacitance-voltage (C-V) carrier profiles is affected by these deep states. To elucidate the characteristics of the interface traps, the deep-level transient spectroscopy (DLTS) measurements are performed. It is found from the DLTS measurements that the electron traps distributed over the energy range of 0.4–0.8 eV below the conduction-band minimum are presented at the InGaP/AlGaAs heterointerface. These interface traps are found to induce an abnormal dependence ofC-Vprofiles and the conduction-band offset on the temperature. The origin of these states and their influence to the electrical and optical properties are also discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365334

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have investigated Mg+Ar and Mg+P dual ion implantation intoAlxGa1−xAswith a wide range of the Al fraction(0⩽x⩽0.75).We characterized the electrical properties and radiation damage of implantedAlxGa1−xAslayers to clarify the effects of dual implantation. Mg+P dual implantation, which maintained a stoichiometric balance, improved the electrical properties inAlxGa1−xAsfor all Al fractions investigated. On the other hand, Mg+Ar dual implantation, which introduces additional radiation damage and increases the number of group III vacancies to enhance the Mg activation, improved the electrical properties inAlxGa1−xAswith a high Al fraction but degraded them inAlxGa1−xAswith a low Al fraction. The difference between Mg+P and Mg+Ar dual implantation is due to the different mechanism of Mg activation enhancement. The effect of keeping the stoichiometric balance is valid regardless of the Al fraction, and increasing radiation damage hardly affects the activation. InAlxGa1−xAswith a high Al fraction, the resistance against implantation damage is large. Here, Mg+Ar dual implantation effectively enhances the Mg activation. Conversely, inAlxGa1−xAswith a low Al fraction, a group III vacancy is easily created by only Mg implantation. Here, radiation damage caused by Mg+Ar dual implantation is too severe to remain even after annealing and degraded Mg activation. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365277

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A comparison of Si doping behavior in GaAs layers on (110) and (001) surfaces under the same growth conditions shows that the autocompensation ratio in (110) layers is usually higher than in (001) layers. However, under certain conditions (low substrate temperature, highAs4pressure, and low Si flux), the free electron concentration in the (110) layers can actually be higher. We attribute this behavior to Ga vacancy traps in the (001) surface layers; whereas layers on the (110) surface remain almost defect free. Our results help to clarify the mechanism of defect generation in the (001) layers, which leads to reduced carrier concentration at low growth temperatures. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365437

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The initial growth stage of phosphorus doped microcrystalline silicon films prepared by plasma enhanced chemical vapor deposition with different plasma excitation frequencies in the range 13.56–116 MHz was studied by Raman and infrared spectroscopy, optical transmission and reflection, and conductivity measurements. The sensitivity of Raman spectroscopy and optical reflection on Si crystallites in the initial growth regime is compared and optical reflection at 4.5 eV is proposed as an easy and reliable tool for this investigation. While the crystallite formation on amorphous silicon substrates at 13.56 MHz is delayed in comparison with glass,SiO2and chromium substrates, nucleation of the crystalline phase on amorphous silicon is found to be greatly enhanced at higher plasma excitation frequencies. On the other hand, for deposition on glass,SiO2,and chromium at frequencies equal to or higher than 70 MHz, increased porosity is found in the initial growth region. The results are interpreted within a model that suggests a conelike initial formation of the silicon crystallites and a higher etching rate of disordered material at high plasma excitation frequencies. In addition, the extension of the process of crystallite formation from the film-plasma interface into a growth zone more than 10 nm deep is proposed. The application of the microcrystalline silicon layers prepared at high plasma excitation frequency is demonstrated in amorphous silicon based tandem solar cells. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365354

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present the results of an investigation on the effects of rapid thermal annealing (RTA) temperature(Tp)and time(tp)on the structural and electrical properties of silicon–silicon oxide systems. X-ray photoelectron spectroscopy (XPS) was used to provide information on the oxide composition of the annealed oxide sample. We found that a higherTpand/or a longertpwill increase the percentage ofSiO2in the annealed oxide layer and thus improve the oxide quality. We also discovered that increasingTpand/ortpwill result in a thicker oxide layer. The suboxide density calculation based on the XPS results indicates that theSi–SiO2interface of our RTA samples is not abrupt. We have used the conclusions obtained from the XPS study to provide satisfactory explanations for the different current versus voltage characteristics exhibited by our tunnel diodes. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365278

出版商:AIP    

年代:1997

数据来源: AIP