摘要:

Relaxation of deep levels in semiconductors is studied through capacitance transients. We explore the temperature‐time duality relationship which is inherent in such thermal relaxation processes. Using duality considerations we show the existence of four distinct spectroscopies. We demonstrate that the techniques for spectroscopic evaluation of capacitance transients are based on differential operators and provide a novel interpretation to spectroscopy. We extend this approach to higher order spectroscopy. Two families of higher order spectroscopy are analyzed using the formalism of temperature‐time duality and differential operators. From duality considerations we have suggested a novel deep level spectroscopy as well as various improvements in line shapes and spectroscopic quality of existing techniques. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358669

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Microwave reflection measurements are widely used for the characterization of minority‐carrier lifetimes in semiconductors. A theoretical description of the technique is presented. The approach is based on a dielectric multilayer model that accounts for experimental parameters such as microwave frequency, sample thickness and doping, and the distance to an optional reflector behind the sample. With a new definition of the sensitivity in transient microwave reflection measurements, the most sensitive configuration is investigated for a given semiconductor thickness and conductivity. Good agreement between the theoretical simulation and measurements is demonstrated. The model is also used for calculating microwave reflection transients from the excess carrier decay after pulsed laser excitation. It is found that the reflected microwave power mirrors the carrier decay if three criteria are fulfilled: The carrier generation must be homogeneous; low‐injection conditions are required; and the reflector must be positioned appropriately for linear dependence of the microwave reflection on the carrier density. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358670

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Current–voltage characteristics, free‐ and trapped‐carrier concentrations, electric field, and excess carrier lifetime contours are given for ap+‐SI‐n+GaAs structure. This analysis is done by numerical simulation of the two carrier drift‐diffusion model of conduction. The dependence of the deep trap parameters and of the semi‐insulating (SI) thickness on theJ‐Vcharacteristic is presented. Particular emphasis will be put on the study of the equivalent resistivity and electric‐field overshoots inside the structure. It is shown that, except for very thick samples, contact and near contact effects on the low‐voltage electrical conduction mechanism are all important. It is then necessary to take into account these effects for a precise and exact interpretation of transport in ap+‐SI‐n+structure. When the deep trap densityNtis high (Nt≫ni), as is the case for compensated (SI) GaAs, the equivalent low current resistivity &rgr; is higher than the equilibrium (unperturbed bulk) resistivity &rgr;e. The nature, electron trap or hole trap, of the deep level affects the equivalent resistivity at intermediate applied voltage. When the density of deep traps is low, &rgr; decreases from values higher than &rgr;eto values lower than &rgr;eas the sample thickness increases. Only in the limit of very thick samples, and then regardless of the trap concentration, does the equivalent resistivity tend asymptotically towards its equilibrium value. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358671

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

GaAs and GaAlAs layers doped with different group VI donors (S, Se, Te) have been exposed to hydrogen plasma. By secondary ion mass spectroscopy, it is shown that, as in Si‐doped materials, the hydrogen diffusion strongly depends on the AlAs content. Electronic transport measurements indicate that after hydrogen diffusion the electron concentration systematically decreases and their mobility increases, demonstrating clearly the passivation of the group VI donors by hydrogen. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359566

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The switching effect induced by an electric field and pressure has been investigated in thin (∼0.5 &mgr;m) films of polydiphenylenephthalide. It has been shown that the conductivity of a polymer film is affected by highly conductive filament formation. Using a liquid crystal, we were able to visualize such filaments and to determine their parameters: size, conductivity, and surface density. The low‐frequency current fluctuations in thin polymer films have also been measured. The rapid growth of current fluctuations near the switching point has been found. The results of this study are evidence for the filament model. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.358672

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Various types of mechanisms for giant magnetoresistance, in particular forf‐electron systems, are critically reviewed. First, the most typical prototype of the nesting‐type magnetic ordering in the heavy‐rare‐earth metals is reviewed. Both negative and positive magnetoresistances are expected for the resistivities, parallel and perpendicular to the nesting wave vector, respectively. Then, the most typical negative magnetoresistance due to impurity states is studied on Eu chalcogenides with chalcogen vacancies or with trivalent rare‐earth impurities substituting Eu atoms. In the former, the change from the singlet to the triplet for the trapped pair electrons is the main origin. In both cases magnetic polarons play important roles. For low‐carrier‐density systems in the metallic region ferromagnetic ordering is induced; the resistivity then has a peak at a temperature near aboveTcdue to a critical scattering resulting a negative magnetoresistance. Narrow‐gap semiconductors and low‐carrier semimetals are also typical materials to show exotic giant magnetoresistance. Various other cases including valence fluctuating systems are also studied. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358673

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An anomalous photovoltaic effect and negative photoconductivity were observed in obliquely deposited thin, amorphous GaAs, Si, and GaAs‐Si films. A model of theE(r&drarr;,k&drarr;)‐relation of amorphous semiconductors shows that some carriers in the extended states can have negative effective masses. The number of these photocarriers is high if the energetic range of the localized states is broad. This can lead to negative photoconductivity. Additionally, gradients of the densities of carriers with positive mobilities in the localized and with negative mobilities in the extended states can lead to diffusion photovoltages of several hundred volts in a single photocell with a length of 10 mm. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.358674

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Starting from an 8*8k⋅pband structure, phonon scattering rates between hole subbands can be calculated with realistic electronic wave functions. Pronounced differences to published light hole and heavy hole scattering rates are found for GaAs, partially due to the density of states of the nonparabolic light hole band and to different overlap between the wave functions. Results are presented for some quantities of interest for transport calculations, like the average velocity after polar LO–phonon scattering. The scattering rates of the split–off holes are calculated within the same formalism. It is shown that their lifetime is mainly limited by optical phonon deformation potential scattering towards the heavy and light hole bands. All band parameters and phonon occupations correspond to room temperature. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358675

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The stationary lattice mobility of holes in bulk GaAs is investigated within a hydrodynamic model, including balance equations for density, current density, and energy density in each hole subband. Generalized hot displaced Maxwellians are used to calculate the input parameters of this model, which are average transport masses for each subband, velocity and energy relaxation rates for the different hole‐phonon scattering channels, and transfer rates between different subbbands. The nonparabolicity of the light hole band produces a strong dependence of its transport mass on the temperature of the light hole distribution. Even for low temperatures, this transport mass is much higher than the parabolic band mass. The velocity and energy relaxation rates are extracted from the phonon scattering rates calculated in the preceeding paper. The contributions of different scattering channels to velocity relaxation depend not only on the scattering rates, but also on the average velocity of the final states after scattering. It is shown that the finite average velocities after interband scattering lead to an intrinsic coupling of the mobilities of light and heavy holes. This makes it impossible to determine the mobilities in each subband separately. Instead, the coupled mobilities are extracted from the stationary solution of the equations of motion of the hydrodynamic model. The resulting hole mobility is in good agreement with measured data up to E=40 kV cm−1if the deformation potentiald0between holes and optical phonons is extracted from the stationary drift mobility at low field: &mgr;0=400±40 cm2/V s and a heavy hole mass ofmh*=0.50±0.02 lead tod0=27.4±5.2(&mgr;0)±3.9(mh*) eV, where the first error is related to the measured mobility and the latter to the dependence of the calculated mobility on the heavy hole mass. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358676

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Modulated free‐carrier absorption (MFCA) is introduced as a novel contactless lifetime mapping technique with high spatial resolution. The advantages of MFCA mapping as compared to other methods are discussed. Examples of lifetime maps on multicrystalline silicon are presented. Solar cells fabricated from identical wafers have been investigated using light beam induced current mapping. Excellent agreement between structures obtained in the measured lifetime and in the current maps was observed. In addition, a quantitative comparison with diffusion lengths determined by local internal quantum efficiency evaluations is presented. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358677

出版商:AIP    

年代:1995

数据来源: AIP