摘要:

The capture kinetics and trapping properties of a dislocation related electron trap detected in strain‐relaxed, compositionally graded Ge0.3Si0.7/Si grown by rapid thermal chemical‐vapor deposition are investigated by deep‐level transient spectroscopy (DLTS). The volume DLTS trap concentration scales linearly with the areal threading dislocation density, as determined by electron‐beam‐induced current measurements on samples with different compositional grading rates, indicating that the detected trap is most likely associated with dislocation core states in these graded structures. The dislocation related trap exhibits both the logarithmic dependence of DLTS peak height on fill pulse timetp, and broadened DLTS peaks which typically characterize carrier trapping at dislocations. These effects are quantified and analyzed to gain insight into the trapping properties of dislocations in GeSi/Si heterostructures and to investigate the effects of dislocation related carrier trapping on DLTS measurements. It is demonstrated that the peak broadening, as characterized by the dimensionless broadening parameter FWHM/Tp, where FWHM andTpare the full width at half‐maximum of the DLTS peak and the DLTS peak temperature, respectively, monotonically decreases with decreasing fill pulse duration, and approaches point‐defectlike behavior fortp<100 &mgr;s.The observed broadening is asymmetric aboutTp, and occurs predominantly on the low‐temperature side of the DLTS peak. This asymmetric broadening is shown to shift the ‘‘apparent’’ trap activation energy, as determined by Arrhenius analysis, fromEC−0.6 eV toEC−0.9 eV (relative to the bulk conduction‐band edge) astpdecreases from 5 ms to 50 &mgr;s. These observations are explained by the presence of a dislocation related distribution of energy levels within the GeSi band gap and the consequent fill‐pulse‐dependent local band bending. The lowest‐energy states within this distribution are preferentially filled with electrons for short fill pulse times. The Arrhenius‐determined ‘‘apparent’’ activation energy is hence interpreted as being a measure of the average energy of the filled defect states, weighted by the density of states distribution in this energy band and by the related fill‐pulse‐dependent local band bending. It is further demonstrated that the minority‐carrier capture cross section may be enhanced by the presence of an attractive coulombic barrier for minority carriers at the dislocations, and we use the logarithmic capture equations to derive a value of 4×10−12cm2for this ‘‘effective’’ capture cross section. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358678

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A real electron beam has finite width, which has been almost universally ignored in electron‐beam‐induced current (EBIC) theories. Obvious examples are point‐source‐based EBIC analyses, which neglect both the finite volume of electron–hole carriers generated by an energetic electron beam of negligible width and the beamwidth when it is no longer negligible. Gaussian source‐based analyses are more realistic but the beamwidth has not been included, partly because the generation volume is much larger than the beamwidth, but this is not always the case. In this article Donolato’s Gaussian source‐based EBIC equation is generalized to include the beamwidth of a Gaussian beam. This generalized equation is then used to study three problems: (1) the effect of beamwidth on EBIC line scans and on effective diffusion lengths and the results are applied to the analysis of the EBIC data of Dixon, Williams, Das, and Webb; (2) unresolved questions raised by others concerning the applicability of the Watanabe–Actor–Gatos method to real EBIC data to evaluate surface recombination velocity; (3) the effect of beamwidth on the methods proposed recently by the author to determine the surface recombination velocity and to discriminate between the Everhart–Hoff and Kanaya–Okayama ranges which is the correct one to use for analyzing EBIC line scans. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358679

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The chemical potential and the capacitance of a 2D circular model quantum dot have been investigated for GaAs, InSb, and Si material parameters, covering a range from a few nanometers to micrometer dimensions. The Schro¨dinger equation has been solved self‐consistently, with the inclusion of many‐body effects, using a local density approximation as well as the optimized Krieger‐Li‐Iafrate exchange potential. Gate structures are included by use of the method of images. We have focused on quantum deviations from classical electrostatic capacitive behavior and found such deviations to be significant even for the material parameters of silicon for feature sizes smaller than 30 nm. The most striking features of quantum dot capacitance are signatures of the dot symmetry analogous to the orbital grouping in atoms: we find structure in the dot capacitance arising from quantum effects in correspondence with the filling of each group of energy‐degenerate orbitals. We also cover the influence of a magnetic field perpendicular to the dot plane and we report some results for the chemical potential vs magnetic field and electron number, assuming an effectiveg‐factor corresponding to the one of bulk gallium arsenide. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358680

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A model is proposed to explain the dependence of the substrate hole current inn‐channel metal‐oxide‐semiconductor field‐effect transistors (MOSFETs) on applied electric field and on oxide thickness. Two types of devices were prepared:n‐channel MOSFETs with gate oxides of 67, 86, and 131 A˚ andp‐channel MOSFETs in which gate oxide thicknesses were almost equal to those in then‐channel MOSFETs. The carrier‐separation technique was used in thep‐channel MOSFETs, and the average energy of hot electrons entering the silicon substrate was obtained. The average energy of the hot electrons is related to the energy distribution of hot holes created by hot electrons emitted from the oxide into then+polysilicon gate during the Fowler–Nordheim electron tunneling in then‐channel MOSFETs. The substrate hole current is numerically modeled as thermionic emission of the hot holes overcoming the energy barrier at the oxide‐n+polysilicon interface. For the gate oxides ranging from 67 to 131 A˚, the dependence of the substrate hole current on the electric field and on oxide thickness is explained by using the average energy of the hot electrons and the thermionic hole emission model. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358681

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Photo Hall concentration and mobility were measured for two molecular beam epitaxy‐grown samples having a silicon planar‐doped structure in the GaAs layer of a GaAs/AlGaAs heterojunction. The nominal silicon concentration for both samples was 1.5×1013cm−2and the distance between the ideal localization of the doped plane and the interface was adjusted to be 15 A˚. The difference between the two samples is the growth direction. The Hall measurements were carried out at 77 K both in darkness and under illumination using an infrared light emitting diode as light source. Photoexcited effects indicate the presence of silicon atoms inside the undoped AlGaAs layer and that the silicon profile spreads mainly in the growth direction. Self‐consistent electronic structure calculations, in the effective‐mass approximations, were performed assuming doping profiles that simulate both samples. The calculations show that parallel conduction occurs when the growth direction is from GaAs to AlGaAs. This is consistent with the Hall measurements. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358682

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A tight‐binding calculation of a Si film with nanometer dimensions is presented. We study the electron energy structure and the wave functions of a pristine Si‐quantum film and one covered with hydrogen. A total energy minimization method, in the framework of self‐consistent tight‐binding theory, is used to investigate the reconstruction of the Si‐surface after the adsorption of hydrogen. The dependence of the electron energy spectrum on the film thickness and the atomic structure of the surface is studied. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358683

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The forward bias and reverse bias current‐voltage characteristics of some gold‐epitaxial CdTe‐on‐InSb Schottky diodes have been measured at room temperature. Series resistance is evident in undoped material (base electron concentration ∼1014cm−3) which has been measured and corrected for and identified as arising from the reverse biased CdTe‐InSb junction. Two straight lines of differing slopes are present in the semilog plots for all the diodes, which we interpret as a bias‐dependent barrier height. The two barrier heights, 0.91±0.04 eV and 0.74±0.02 eV, are well known in the Au‐CdTe system, from which we conclude that two discrete states are present at the CdTe‐Au interface. The occupancy of the states is determined by the applied bias, and hence the barrier height changes. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358614

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In this article noise measurements on amorphous siliconnipandpindiodes are presented and discussed with regard to standard models for flicker noise. It is shown that 1/fnoise is present in the dark forward current ofa‐Si:H diodes as well as in the photocurrent at low forward or reverse bias. The dependence of the noise power spectral density on dark current and photocurrent density, diode area, thickness, and current aging leads us to the conclusion that fluctuations in the electron injection current at then+contact are the reason for 1/fnoise. This model is further supported by the current and frequency dependence of the shot noise in the photocurrent. We assume that the trapping of carriers switches on and off current filaments in the diode interface layer. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358615

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Atomic force microscopy used in the resonant mode is a powerful tool for measuring local surface properties: for example, the quantitative analysis of the electrical forces induced by the application of an electric field between a conductive microscope tip and a surface allows the determination of the tip/surface capacitance and the local surface work function. However, these quantitative analyses require knowledge of tip geometry. In this article, we show that the simple procedure of evaluating the tip curvature radius by fitting the variations of the electrostatic force with the tip‐surface distance is not always adapted to the case where one of the tip‐surface system elements is a semiconductor. However, particular experimental conditions are determined to overcome these difficulties. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358616

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Deep‐level transient spectroscopy has been used to study the deep levels introduced by silver impurity in silicon. New levels in addition to the well‐known silver‐related deep donor and acceptor levels have been found. Interaction of silver‐related defects with radiation‐induced defects has been studied using &agr; irradiation. Data on the annealing characteristics of silver‐related levels are reported. Isochronal thermal annealing before and after irradiation provides interesting insights on such interactions and on the nature of the silver‐related levels. In particular, the two newly observed prominent silver‐related levels exhibit a complementary annealing behavior, suggesting a mutual thermal transformation. The presence of silver is seen to produce a significant change in the annealing characteristics of the prominent radiation‐inducedA‐center defect. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358617

出版商:AIP    

年代:1995

数据来源: AIP