摘要:

A generic expression is presented for the valence‐band structure of strained group‐IV semiconductors (Si, Ge, and Si1−xGexalloys) that takes into account spin‐orbit coupling. The valence band is obtained usingk⋅pperturbation theory coupled with deformation potential theory. The band‐structure equation is put into a simplified form that can be readily used, viz., ∑i=03∑j=03−iaijEkjk2i=0, wherekis the wave‐vector magnitude,Ekis the energy atk, and the coefficientsaijare functions of band parameters and strain components. The band structure of strained silicon is qualitatively analyzed in relation to the well‐established piezoresistivity coefficients. Furthermore, a new coefficient is introduced that describes the first‐order change in carrier concentration effective mass per unit applied stress for different stress directions.

ISSN:0021-8979    

DOI:10.1063/1.353287

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A considerable improvement in the accuracy of the measurement of the intrinsic carrier concentration in silicon near room temperature has recently been reported. This was achieved by the accurate analysis of minority‐carrier current flow in specially fabricatedp‐njunction devices. In this paper this technique has been extended to measurements down to 77 K. A further improvement of the technique has been the simultaneous measurement of the minority‐carrier electron mobility utilizing open‐circuit voltage decay measurements.

ISSN:0021-8979    

DOI:10.1063/1.353288

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A Monte Carlo method is proposed to study Auger recombination effects in semiconductors, which is general enough to study these effects in one (1D), two, or three dimensions, to accommodate arbitrary band structures, and to use either Boltzmann or Fermi–Dirac statistics. Auger recombination coefficients can readily be extracted from Monte Carlo calculation results, and distributions of each species of carriers that are involved in the recombination process are also obtained. Calculation results using this Monte Carlo method are compared against results obtained from previous work. In 1D cases, the Monte Carlo results agree very well with those previously obtained. It is also shown that results previously derived are applicable only to 1D cases. This is because in higher dimensions, considerations of the higher degree of freedom, which are not incorporated in previous work, are necessary. All in all, the Monte Carlo method proposed in this article is expected to provide useful insight into Auger recombination effects, and directions for bandgap engineering towards design of material less prone to such effects.

ISSN:0021-8979    

DOI:10.1063/1.353289

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We present a study of spectral‐ and time‐resolved reflectivity and transmission measurements on hydrogenated amorphous silicon (a‐Si:H) with 50 fs time resolution. Electron‐hole pairs are photoexcited into the extended states ofa‐Si:H by an ultrashort pump pulse at ℏ&ohgr;=2 eV. The temporal evolution of the photoinduced optical response is studied for a broad range of excitation densities from 1018up to 1020cm−3, and on a timescale of up to 200 ps. The temporal evolution of the optical response is discussed in terms of recombination and trapping mechanisms for carriers in the extended states ofa‐Si:H.

ISSN:0021-8979    

DOI:10.1063/1.353263

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Calculation of third‐order bounds to the conductivity of isotropic two‐component composites is discussed. Coincidence of the Beran bounds and bounds derived using trial fields based on the solution of a single‐body electrostatic boundary‐value problem is demonstrated for a random distribution of impenetrable ellipsoids. This extends a proof of Beasley and Torquato [J. Appl. Phys.60, 3576 (1986)]. A structural parameter related to third‐order bounds is calculated for a face‐centered cubic array of cubes in a matrix. For an array of rectangular blocks an upper bound in one direction is derived. This bound, and its two‐dimensional analogs, become very sharp in the limit of strong inhomogeneity. Improved third‐ and fourth‐order bounds for the three‐dimensional checkerboard are presented.

ISSN:0021-8979    

DOI:10.1063/1.353264

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Delayed collection field experiments, which are known to be a method for measuring lifetimes in amorphous semiconductors, are examined for amorphous arsenic triselenide. It is experimentally shown that the effective transit time is approximately equal to the delay time, when the delay time is long compared with the zero‐delay transit time, and that the effective transit time is almost independent of collection electric field and temperature. These results are found to be consistent with the prediction by Kastner [Solid State Commun.45, 191 (1983)], which is based upon the multiple trapping model. Influence of a structured, tail‐state distribution on the experimental results has been also numerically examined.

ISSN:0021-8979    

DOI:10.1063/1.353265

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The effects of the substrate temperature on the composition and microstructure of Bi‐Sb‐Te‐Se thin films are discussed and related to the Seebeck coefficient and resistivity. The films were prepared on silica substrates by argon ion beam sputtering. The effect of subsequent heat treatment is also discussed. The composition becomes stoichiometric at the substrate temperature around 500 K at which the Seebeck coefficient has a maximum and the resistivity has a minimum. The Seebeck coefficient changes its sign at the substrate temperature around 340 K. The crystal structure of the films deposited at room temperature is identified as the rock‐salt type, and the change of the thermoelectric properties as a function of the substrate temperature can be mainly attributed to the volume fraction of the Bi2Te3and rock‐salt structures. The subsequent heat treatment is effective in improving the power factor of the stoichiometric thin films.

ISSN:0021-8979    

DOI:10.1063/1.353266

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Photoinduced discharge is a common experimental technique for studying photogeneration and carrier transport in photoconductors. Although the technique was first devised for discharge with strongly absorbed light and trap‐free transport, its application to systems with bulk‐generated carriers and/or trap‐controlled transport is becoming more important. It is noted that in the latter case, a finite error can be introduced by using the existing formula for data analyses. This paper describes a generalized method of deducing electronic transport and photogeneration properties from photoinduced discharge characteristics.

ISSN:0021-8979    

DOI:10.1063/1.353267

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

An extensive photoreflectance (PR) study has been done on a series of undoped andn‐type, InGaAs and InAlAs molecular beam epitaxy (MBE) grown layers with different In mole fractions, and epilayer thicknesses on Fe‐doped semi‐insulating (SI)‐InP substrates. Three substrate features were observed in the spectra. From investigations of the temperature dependence, time constant dependence, and an additional cw light beam intensity dependence, they were identified as an excitonic transition from the substrate, a free electron transition near the interface which gives a Franz–Keldysh oscillation, and a transition from the spin–orbit split‐off valence band. The Franz–Keldysh effect indicates that a temperature dependent built‐in electric field is formed near the interface. The dependence of the field on doping concentration, strain, or epilayer composition (band gap) was insignificant. The PR signal from a SI‐InP wafer after a pre‐MBE‐growth heating was found to be strongly enhanced over that from an untreated wafer. This signal was even more enhanced after an epilayer was grown on top, indicating the formation of a built‐in field. These results are indicative of a redistribution of charge near the interface/surface in the process of MBE growth; the associated PR signal (phase) could be used forinsitumonitoring of epilayer growth on SI‐InP wafers.

ISSN:0021-8979    

DOI:10.1063/1.353268

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Current‐voltage (I‐V) characteristics of GaAs Schottky and tunnel metal–insulator–semiconductor diodes were measured at various temperatures between 100 and 400 K and analyzed on a basis of an interfacial layer model recently proposed by Maeda, Umezu, Ikoma, and Yoshimura [J. Appl. Phys.68, 2858 (1990)]. The ideality factornobtained from the forwardI‐Vcharacteristics increased from about 1.05–1.1 to 2–3 as the temperature was decreased from 400 to 100 K. This could be interpreted as an increase in the electron occupation ratio of the interface states with decreasing temperatures. Precise measurement of thenvalue of theI‐Vcurve revealed anomalous behavior as a function of the forward current, which was not observed in either amorphous or crystalline Si Schottky diodes. This seems to be related to the presence of a density peak in the interface state distribution like those proposed by Spicer, Newman, Spinat, Liliental‐Weber, and Weber, [J. Vac. Sci. Technol. A8, 2084 (1990)]. The interfacial Fermi level was demonstrated to move from the metal Fermi level as applied voltage is increased, but it hardly moved relative to the conduction band bottom. This is considered to be the first direct evidence of Fermi level pinning inI‐Vcharacteristics.

ISSN:0021-8979    

DOI:10.1063/1.353269

出版商:AIP    

年代:1993

数据来源: AIP