摘要:

The partitioning of point defect species during diffusion controlled precipitation of a misfitting compound in Czochralski silicon is studied using the principle of maximum degradation rate of the total system free energy. The degradation rate of the system free energy is obtained from the entropy production due to mass diffusion in the matrix. The results are then compared with those obtained using the principle of maximum growth rate. It is shown that, for a precipitation process involving more than one chemical or structural component species with their concentrations deviating from the appropriate thermal equilibrium values, the maximum growth rate description does not generally correspond to that of the maximum degradation rate of the system free energy. The results are then applied to oxygen precipitation in silicon, showing some equilibrium characteristics pertinent to a multicomponent system with intrinsic point defects acting aspseudocomponents. It is also shown that, depending on the intrinsic point defect concentrations at the far field of diffusion, the oxide precipitate can grow either by emitting or by absorbingbothvacancies and Si self‐interstitials. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359197

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Deep level transient spectroscopy has been used to investigate the effects of alpha irradiation and thermal annealing on deep levels in gold‐dopedn‐type silicon. Data on thermal annealing characteristics of the well‐known gold acceptor up to temperatures as high as about 600 °C are reported. This level is found to be very stable, supporting the substitutional gold model for the acceptor center. Interaction of the gold‐related defects with radiation‐induced defects has been investigated using 5.48 MeV alpha particles for irradiation, combined with isochronal thermal annealing before and after irradiation. Irradiation produces the usual radiation‐induced levels. A slight reduction in the gold‐acceptor concentration is observed due to irradiation, contrary to an earlier reported study. A noticeable suppression of the thermal stability of this level is also observed after irradiation. The presence of gold leads to a significant enhancement of the anneal‐out temperature of the well‐knownA‐center defect. A deep level atEc−0.34 eV, ascribed to the Fe–Au complex, is found to be enhanced by irradiation. No evidence is found to support the recently proposed gold‐divacancy complex model of the gold acceptor—rather, the results strongly support the isolated substitutional impurity model for this center. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.359198

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

He+and N+ion irradiation of epitaxialp‐type In0.76Ga0.24As0.58P0.42and In0.53Ga0.47As was performed at 300 K to obtain high‐resistivity regions. In both the ternary and quaternary samples the resistivity first increases with ion dose. A maximum is reached at a critical dose depending on the ion species and initial doping concentration. Above this dose the conductivity converts tontype and the resistivity steadily decreases to ∼102&OHgr; cm in InGaAsP and ∼2 &OHgr; cm in InGaAs. After thermal annealing the type converted samples revert toptype. However, for ion doses ≥1013cm−2the high resistivities remain stable up to 700 K. The results suggest that simple point defects, rather than complexes are responsible for the changes in the electrical properties of the samples. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359199

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Positron lifetime investigations of vacancy distributions in ingots of silicon have shown that vacancies are retained after growth at nearly constant concentrations close to 3×1016cm−3. The vacancies are generally monovacancies and are suggested to be trapped by oxygen clusters. Trapped divacancies can also be formed but they are unstable upon heat treatment at 1000 °C for 16 h. This observation is invoked to explain anomalous oxygen precipitation. This heat treatment has little effect on the distributions of monovacancies in the ingots investigated, so the complexes between vacancies and oxygen clusters are suggested to be formed at temperatures above 1000 °C during the growth. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359200

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Analytical and optimization methods of determining all elastic constants of elastically anisotropic solids from the group velocities measured in various directions in the symmetry planes are described. The group velocities in various directions of the specimen are measured, using broadband pointlike and line‐type sources in combination with pointlike detectors, and changing a source‐to‐detector orientation. The mixed index elastic constants of the specimen are determined using analytic formulas that relate the elastic constants to the group velocity in an arbitrary direction on the symmetry plane. It is demonstrated that given the numerous group velocity data, one can efficiently determine the elastic constants by first converting them into phase velocity data and then applying the least‐squares optimization methods to the phase velocity data. Examples are provided with specimens of transversely isotropic zinc, cubic silicon, and orthotropic fiber‐reinforced poly ether ether kethon. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359201

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A closed‐form solution is presented for the stresses induced in an infinite elastic body by a periodic array of misfitting inclusions. This solution is used to study the mechanical and electronic properties of buried arrays of [11¯0]‐oriented strained quantum wires. A critical mismatch condition along the lines of the Matthews and Blakeslee condition for strained layers is developed and is used to show that quantum wire structures should be extremely stable in the postgrowth processing stages provided that the repeat period of the array is more than four times the dimension of a wire. If the period is more than five times the wire dimension then each member of the array behaves like an isolated wire. It is shown that stability problems for closely spaced arrays may be avoided by choosing the direction in which the wires are periodically distributed to be [001] rather than [110]. The formulas are also used to investigate the difference between the strain‐induced band gap shifts of quantum wires and wells experiencing the same lattice mismatch with the growth substrate. It is found that the dilatation is identical in the two structures so that, in the InGaAs system, wells and wires of the same composition should have very similar band gaps. By contrast, conduction‐band splitting in the GeSi system can give rise to differences of up to 100 meV between the band gaps of the two structures. These results are shown to compare very favorably with experiment. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359202

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Chemical vapor deposited 3C‐SiC films were micromachined into free standing cantilevers and their anelastic and elastic properties were determined by a vibrating reed technique. Despite a high density of defects, epitaxial 3C‐SiC exhibits extremely high mechanicalQwhich is essential for resonator sensors and actuators. An anelastic relaxation peak was found with an associated activation energy of 0.94 eV. Doping caused splitting of this peak. The mechanism of the mechanical relaxation peak is discussed in relation to defect movement under stress. Young’s modulus of epitaxial undoped 3C‐SiC was found to be 694 GPa,p‐doping reduced it to 474 Gpa. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359551

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The Al‐Ga interdiffusion induced by Si focused ion beam implantation and subsequent rapid thermal annealing (RTA) was investigated in an Al0.3Ga0.7As/GaAs superlattice structure with equal 3.5 nm barrier and well widths. Si++was accelerated to either 50 or 100 kV and implanted parallel to sample normal at doses ranging from 1013to 1015/cm2. The effect of rapid thermal anneal of 10 s at 950 °C was characterized by the secondary ion mass spectrometry technique. In the implanted region, the interdiffusion causing compositional mixing was significantly enhanced by the Si implantation. An ion dose as low as 1×1014/cm2results in a two‐order of magnitude increase in the interdiffusion coefficient, to a value of 4.5×10−14cm2/s, producing a mixing effectiveness of ∼90%. In contrast, the RTA‐only case produces an interdiffusion coefficient of 1.3×10−16cm2/s and very little mixing. A strong depth dependence of the mixing process was observed at 100 keV implantation energy, with a ‘‘pinch‐off’’ (more heavily mixed) region being formed at a certain depth. It is noticed that the depth where this enhancement occurred is not associated with either the maximum concentration of Si ions or of vacancies. Instead, it coincides with the positive maximum of the second derivative of the vacancy profile, which in turn represents a maximum in the vacancy injection generated by the presence of a transient vacancy concentration gradient. Based on these findings, a theoretical model was developed using vacancy injection as responsible for mixing. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359203

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A method is proposed for the determination of the state of an impurity (donor, acceptor, or deep level) in semiconductor lattice. To demonstrate the method boron was diffused into type Ia natural diamond under a dc electric field. The concentration and diffusion profiles of boron were affected by the applied field. Boron diffuses as a negative ion since it is an acceptor shallow enough to be partially ionized at the temperature of diffusion. The drift velocity of boron ions at the temperature of diffusion was also estimated. The diffusion of lithium and oxygen from a Li2CO3source in chemical vapor deposited diamond films was performed under bias at 1000 °C in an argon atmosphere. After diffusion, the concentrations of Li, O, and H in the diamond films were found to be around (3–4)×1019cm−3. No dependence of these concentrations on the applied bias was observed. It was found that the diffusion of Li goes primarily through grain boundaries, which may explain why it does not depend on the applied voltage. Fluorine was present as an impurity in the dopant source. Its concentration in the films was around (1–2)×1017cm−3and did depend on the applied bias, indicating that fluorine may have formed a shallow level in the diamond band gap. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359204

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A study of high‐concentration boron diffusion using a precipitation model is presented in this paper. Recent experimental results on the annealing of boron implanted in preamorphized silicon give the opportunity to analyze, with the help of simulations, the precipitation kinetics and the effect of dislocation loops existing at the amorphous/crystalline interface. A nonequilibrium point‐defect diffusion model is used throughout the study, including explicitly the equations describing the kinetics of precipitation. The initial conditions take into account the high level of activation observed experimentally after the solid‐phase epitaxy. This influences both the sheet resistance and the doping profile shape at the end of the process. In addition, it is shown that a proper modeling of these diffused profiles includes the effect of the dislocation loops at the amorphous/crystalline interface, acting as a sink term for the interstitials. A more classical formulation of the diffusion equation does not require the modeling of such phenomena since the equilibrium concentration of the point defects is implicitly assumed. Finally, other applications to high‐concentration boron diffusion are presented, demonstrating the range of validity of the involved parameters. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359205

出版商:AIP    

年代:1995

数据来源: AIP