摘要:

A Cr oxide layer produced by the deposition of Cr onto a condensed H2O overlayer on a GaAs(100) wafer atT=90 K was studied using synchrotron radiation photoemission. Cr reacted with H2O immediately upon deposition at low temperature resulting in the synthesis of hydrated Cr oxide compounds, and then formed a stable dry oxide as the temperature of the substrate was raised toward room temperature and eventually 400 °C. The oxide was stable up to a temperature of at least 400 °C, although the substrate did show changes indicative of reaction.

ISSN:0021-8979    

DOI:10.1063/1.353214

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A quantum statistical formalism has been developed for the excitonic luminescence linewidths and line shapes in semiconductor binary alloys due to band‐gap fluctuations caused by the random distributions of the alloy components in an applied magnetic field. The virtual crystal approximation is used to estimate the local band‐gap variations. The shifts of the excitonic transition energy due to the band‐gap fluctuations are obtained using the first‐order perturbation theory. A Gaussian line shape is obtained for the excitonic transition using standard statistical techniques. This formalism is applied to calculate the linewidths and line shapes associated with the ground‐state excitonic transition as a function of alloy composition and magnetic‐field strength in AlxGa1−xAs and InxGa1−xP alloys. The resulting linewidths and line shapes are in good agreement with the available low‐temperature photoluminescence data; however, the calculated linewidths are consistently smaller than the measured values. The possible mechanisms responsible for this discrepancy are discussed. A comparison of excitonic linewidths obtained from the present theory with those calculated earlier is also presented.

ISSN:0021-8979    

DOI:10.1063/1.353215

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

In silver‐doped silicon, several new electron paramagnetic resonance spectra were observed. Three of these, labeled Si‐NL45, Si‐NL46, and Si‐NL47, were detected inn‐type samples. The spectra have trigonal symmetry; the effective electron spin valueSequals 1/2. The spectra Si‐NL45 and Si‐NL46, with the perpendiculargvalues close to 6 and 8, can alternatively be described by electron spinsS=5/2 andS=7/2, respectively, andgvalues close to 2. The Si‐NL47 center has both principalgvalues significantly deviating from 2. They can be accounted for by taking crystal‐field splitting and spin‐orbit coupling into consideration. On the basis of the correlation of the production of these centers with the Si‐NL44 center and the analysis with high values of electron spin, all these centers are tentatively identified as silver‐related complexes.

ISSN:0021-8979    

DOI:10.1063/1.353188

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Deep‐level transient charge spectroscopy (QDLTS) measurement is described. The technique is used to investigate energy levels of tin in AlxG1−xAs. The QLDTS spectra have multiple peaks which show the multilevel nature of the tin donors.

ISSN:0021-8979    

DOI:10.1063/1.353189

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The lock‐on effect—observed in high‐power GaAs and InP photoconductive switches—is characterized by a high on‐state conduction current resulting from a high gain switching mechanism. In our study, an analytical model has been developed to determine the fundamental limitations to device performance imposed by this effect on high‐power switching devices. In this model, a regional approximation is used to calculate the field distribution in the device and to obtain the device’s current density‐voltage (J‐V) characteristics. It is shown that negative resistance gives rise to high‐field avalanche injection at the anode boundary. Moreover, the analytical results indicate the importance of electron velocity saturation for the onset of negative resistance, as well as the effect of hole injection from the high‐field anode region on voltage lowering across the switch. It is determined that lock‐on is associated with the transferred‐electron effect, and will therefore constrain the use of GaAs and InP as materials for high‐power switching devices.

ISSN:0021-8979    

DOI:10.1063/1.353190

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Low and high electric field transport in the CdIn2Te4electro‐optical semiconductor were investigated. The conductivity, the carrier concentration, and the mobility were measured versus the temperature using Hall techniques. Nonlinear current‐voltage characteristics in high fields are interpreted in terms of thermal effects, not in terms of space‐charge‐limited currents as usually encountered. The nonreversibility ofI‐Vmeasurements is also discussed, diffusion of species are proposed to explain the change of activation energy of the conductivity.

ISSN:0021-8979    

DOI:10.1063/1.353191

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The logarithmic electrical resistivities of pentacene (PEN) thin films doped with iodine in the direction parallel to the substrate plane fit theT−1/3dependence well. This indicates that the lateral transport of the film was governed by two‐dimensional variable range hopping. In contrast, the logarithmic resistivities of the films perpendicular to the substrate were observed to be almost independent of temperature and to be weaklyT−1/2dependent. This shows that the tunneling mechanism is predominant in perpendicular transport. Two‐dimensional conduction of the film was confirmed by these transport properties, which was expected from the intercalated structure of PEN film doped with iodine.

ISSN:0021-8979    

DOI:10.1063/1.353192

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The irreversible isothermal annealing of the as‐deposited defects of hydrogenated amorphous silicon,a‐Si:H, deposited at room temperature by concentric‐electrode radio‐frequency glow discharge is studied using dark and photoconductivity, space‐charge limited current, and time‐of‐flight. The photoconductivity increases as a power law of the annealing time with exponent 0.8. The density of states at the Fermi level, measured by space‐charge limited current, is inversely proportional to the annealing time. These results are compatible with bimolecular annealing kinetics. The dark conductivity obeys a Meyer–Nelder rule during the isothermal anneal.

ISSN:0021-8979    

DOI:10.1063/1.353167

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Schottky diodes utilized for mechanical stress effect studies were fabricated using aluminum contacts to polycrystalline diamond thin films grown by a hot‐filament‐assisted chemical vapor deposition process. Compressive stress was found to have a large effect on the forward biased current‐voltage characteristics of the diode, whereas the effect on the reverse biased characteristics was relatively small. This stress effect on the forward biased diamond Schottky diode was attributed to piezojunction and piezoresistance effects that dominated the diode current‐voltage characteristics in the small and large bias regions, respectively. At a large constant forward bias current, a good linear relationship between output voltage and applied force was observed for force of less than 10 N, as predicted by the piezoresistance effect. The measured force sensitivity of the diode was as high as 0.75 V/N at 1 mA forward bias. Compared to either silicon or germanium junction diodes and tunnel diodes, polycrystalline diamond Schottky diodes not only are very stress sensitive but also have good linearity. This study shows polycrystalline diamond Schottky diodes have potential as mechanical sensors.

ISSN:0021-8979    

DOI:10.1063/1.353168

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Nonlinearity of the piezoresistance effects inp‐ andn‐type silicon was measured at room temperature for three surface impurity concentrations and for three crystallographic orientations <100≳, <110≳, and <1¯1¯2≳. Piezoresistance coefficients up to third order in stress were obtained experimentally. Uniaxial stresses up to about 174 MPa were applied with currents flowing either parallel (longitudinal configuration) or perpendicular (transverse configuration) to them. A complete set of nine independent second‐order tensor components was determined. The second‐order piezoresistance coefficients in various configurations of uniaxial stress, current, and crystallographic orientation were calculated by the sixth rank tensor transformation. The nonlinear piezoresistance effect inn‐type silicon was discussed with the many‐valley model.  

ISSN:0021-8979    

DOI:10.1063/1.353169

出版商:AIP    

年代:1993

数据来源: AIP