Measurements of electrical properties using the Van der Pauw technique have been made on the n-type and p-type silicon carbide single crystals and epitaxial layer having resistivity from 10-3 to 102 ohm-cm. Experiments on the selection of measuring conditions and comparison between the Van der Pauw method and the conventional method have been performed. It is found that the magnitude and stability of contact resistance greatly affect the measuring results. Among the pressure contacts studied, indium contact has the lowest contact resistance, while copper, tin, and phosphor-bronze contacts must be electrically formed before use. With different electrode materials and sample currents, the deviation of values obtained is about 2%. It is suggested that the sample current should be chosen in accordance with the resistivity and contact resistance of the specific sample. As compared with the conventional method, the Van der Pauw method can give higher precision and reproducibility. High temperature electrical properties of silicon carbide single crystals have been measured in a temperature range from room temperature to 1000°K, and the ionization energy of nitrogen donors is found to be 0.056 eV. Anomalous phenomena that result in experimental errors and their origins are discussed.
Measurements of electrical properties using the Van der Pauw technique have been made on the n-type and p-type silicon carbide single crystals and epitaxial layer having resistivity from 10-3 to 102 ohm-cm. Experiments on the selection of measuring conditions and comparison between the Van der Pauw method and the conventional method have been performed. It is found that the magnitude and stability of contact resistance greatly affect the measuring results. Among the pressure contacts studied, indium contact has the lowest contact resistance, while copper, tin, and phosphor-bronze contacts must be electrically formed before use. With different electrode materials and sample currents, the deviation of values obtained is about 2%. It is suggested that the sample current should be chosen in accordance with the resistivity and contact resistance of the specific sample. As compared with the conventional method, the Van der Pauw method can give higher precision and reproducibility. High temperature electrical properties of silicon carbide single crystals have been measured in a temperature range from room temperature to 1000°K, and the ionization energy of nitrogen donors is found to be 0.056 eV. Anomalous phenomena that result in experimental errors and their origins are discussed.
A method for measuring the minority carrier lifetime in silicon carbide semiconductor by the injection electroluminescence at point contacts is presented. The principles involved and measuring equipment used are described. Experiments on some important factors, such as resonance disturbance, electrical properties and electroluminescence characteristics of the point contacts, have been performed. Some feasible precautions that must be taken in order to avoid resonance disturbance and contact by-passing and to control rectification ratios are described. It is shown that in order to ensure reliability of experimental results, a knowledge of the electroluminescence characteristics of the samples should be required before measuring. By means of this method, the minority carrier lifetimes for some silicon carbide single crystals have been measured, and for most crystals these values are found to be smaller than 4.2×10-9 sec.
A method for measuring the minority carrier lifetime in silicon carbide semiconductor by the injection electroluminescence at point contacts is presented. The principles involved and measuring equipment used are described. Experiments on some important factors, such as resonance disturbance, electrical properties and electroluminescence characteristics of the point contacts, have been performed. Some feasible precautions that must be taken in order to avoid resonance disturbance and contact by-passing and to control rectification ratios are described. It is shown that in order to ensure reliability of experimental results, a knowledge of the electroluminescence characteristics of the samples should be required before measuring. By means of this method, the minority carrier lifetimes for some silicon carbide single crystals have been measured, and for most crystals these values are found to be smaller than 4.2×10-9 sec.
The crystal structure of Mn3Ga has been determined by means of the X-ray powder method. The unit cell is hexagonal, with a = 5.4065?, c = 4.3537?, and c/a = 0.8053 at 20℃ for the alloy containing 26.8 at. % Ga. The space group is D6h4-P63/mmc. Each unit cell contains two formula units, the six Mn atoms being situated at the 6(h) positions with xh = 0.837, and the two Ga atoms at the 2(c) positions. It is a deformed form of the DO19 type close-packed ordered structure. The homogeneity range corresponding to this structure in the Mn-Ga system does not include the ideal composition however, but is displaced to the Ga-rich side.
The crystal structure of Mn3Ga has been determined by means of the X-ray powder method. The unit cell is hexagonal, with a = 5.4065?, c = 4.3537?, and c/a = 0.8053 at 20℃ for the alloy containing 26.8 at. % Ga. The space group is D6h4-P63/mmc. Each unit cell contains two formula units, the six Mn atoms being situated at the 6(h) positions with xh = 0.837, and the two Ga atoms at the 2(c) positions. It is a deformed form of the DO19 type close-packed ordered structure. The homogeneity range corresponding to this structure in the Mn-Ga system does not include the ideal composition however, but is displaced to the Ga-rich side.
It is shown that by means of the solutions obtained by the random phase approximation, the generalized configuration mixing (GCM) method can provide better approximate solutions in a rather simple and systematic way. A set of explicit expressions for the matrixelements involved in the eigenvalue equation of the GCM method has been derived. Further, it is proved that the GCM method is self-consistent, and the equation of motion satisfied by the corresponding Green function and its series expansion have been obtained. By means of the latter, the property of the eigensolution determined by the GCM method is discussed.
It is shown that by means of the solutions obtained by the random phase approximation, the generalized configuration mixing (GCM) method can provide better approximate solutions in a rather simple and systematic way. A set of explicit expressions for the matrixelements involved in the eigenvalue equation of the GCM method has been derived. Further, it is proved that the GCM method is self-consistent, and the equation of motion satisfied by the corresponding Green function and its series expansion have been obtained. By means of the latter, the property of the eigensolution determined by the GCM method is discussed.
In this paper, we formulate an intermediate boson (denoted as IB) theory based on the following assumptions: there are 8 images ω1,…,ω8 of IB, transforming as the octet of SU3, coupling with 8-dimensional hadron current to form an unitary singlet Lagrangian Lw; but either in real or in virtual states, only 4 kinds of particles(W±, W0, W0-4 linear combinations of ω1,…,ω8) can occur. The incompletenessof virtual IB states, which is the very source of isospin and strangeness nonconservation in weak processes, can be described by a projection operator ξ=|W+>+| + |W->-|+|W0>0|+|W0>0| used for intermediate states. If assuming further the lepton currents to couple directly with W±, one can obtain a theory giving unified description for all weak processes. When applied to leptonic decays, our theory leads directly to that identical with Cabibbo's, and explains his hypothesis of 'unit length' in a natural way (as a result of probability normalization). When applied to nonleptonic decays, our theory includes the |ΔI| = 1/2 rule.
In this paper, we formulate an intermediate boson (denoted as IB) theory based on the following assumptions: there are 8 images ω1,…,ω8 of IB, transforming as the octet of SU3, coupling with 8-dimensional hadron current to form an unitary singlet Lagrangian Lw; but either in real or in virtual states, only 4 kinds of particles(W±, W0, W0-4 linear combinations of ω1,…,ω8) can occur. The incompletenessof virtual IB states, which is the very source of isospin and strangeness nonconservation in weak processes, can be described by a projection operator ξ=|W+>+| + |W->-|+|W0>0|+|W0>0| used for intermediate states. If assuming further the lepton currents to couple directly with W±, one can obtain a theory giving unified description for all weak processes. When applied to leptonic decays, our theory leads directly to that identical with Cabibbo's, and explains his hypothesis of 'unit length' in a natural way (as a result of probability normalization). When applied to nonleptonic decays, our theory includes the |ΔI| = 1/2 rule.
In this paper; we have applied the intermediate boson theory to discuss the nonleptonic decays of hyperons. The various mechanisms of the nonleptonic decays are considered, the 'FMS pole' is explained, and the dynamical basis of the sum1 rule 2 Ξ--= Λ-0+31/2∑0+ is given. The decay rates and asymmetries are calculated, and the results are consistent with the experimental data.
In this paper; we have applied the intermediate boson theory to discuss the nonleptonic decays of hyperons. The various mechanisms of the nonleptonic decays are considered, the 'FMS pole' is explained, and the dynamical basis of the sum1 rule 2 Ξ--= Λ-0+31/2∑0+ is given. The decay rates and asymmetries are calculated, and the results are consistent with the experimental data.
In this paper we have obtained a representation of the S matrix element for a potential with the following properties: 1) it posseses a singularity higher than r-2 near the origin. 2) it asymptotically decreases faster than any exponent at infinity.
In this paper we have obtained a representation of the S matrix element for a potential with the following properties: 1) it posseses a singularity higher than r-2 near the origin. 2) it asymptotically decreases faster than any exponent at infinity.
For the highly singular potential satisfying the conditions of ref. (Ⅰ), it is proved that the partial wave S-matrix element posseses the asymptotic behaviour S(λ,k)～Ce-nImλ as the imaginary values of angular momentum tending to infinity. From this we obtained the following conclusions:(1) The WATSON-SOMMERFELD transformation of the scattering amplitude does not hold.(2) Using the result of ref. (I) and above equation, we get existance of REGGE poles with real part tending to infinity in the little angle neighbourhood of the imaginary axis.
For the highly singular potential satisfying the conditions of ref. (Ⅰ), it is proved that the partial wave S-matrix element posseses the asymptotic behaviour S(λ,k)～Ce-nImλ as the imaginary values of angular momentum tending to infinity. From this we obtained the following conclusions:(1) The WATSON-SOMMERFELD transformation of the scattering amplitude does not hold.(2) Using the result of ref. (I) and above equation, we get existance of REGGE poles with real part tending to infinity in the little angle neighbourhood of the imaginary axis.
The dependence of absolute values and the relative behavior of a reduced width of Po odd isotopes upon nuclear model wave functions and the radius R0 are investigated, the radius R0 ranging from 8 f to 9.5 f. The results of calculation show that the single configuration wave function and BCS wave function are unsatisfactory, the projected wave function with blocking is better, while the projected wave function without blocking is best. The ratio of the a reduced width of Po211 and the neighboring even A isotope Po210 is insensitive to R0, and is in agreement with the experimental value within ±20%. Compared with experimental data, absolute values of a reduced width and their variation versus mass number A can be satisfactorily described by the projected wave function without blocking, if R0 is taken to be about 8 f.
The dependence of absolute values and the relative behavior of a reduced width of Po odd isotopes upon nuclear model wave functions and the radius R0 are investigated, the radius R0 ranging from 8 f to 9.5 f. The results of calculation show that the single configuration wave function and BCS wave function are unsatisfactory, the projected wave function with blocking is better, while the projected wave function without blocking is best. The ratio of the a reduced width of Po211 and the neighboring even A isotope Po210 is insensitive to R0, and is in agreement with the experimental value within ±20%. Compared with experimental data, absolute values of a reduced width and their variation versus mass number A can be satisfactorily described by the projected wave function without blocking, if R0 is taken to be about 8 f.
This paper is intended to describe the properties of nonreciprocal microwave ferrite devices from the four-terminal network analysis. First, the impedance and the scattering matrix of an X-band rectangular waveguide containing a transversely magnetized ferrite post are measured as a function of the (1) diameter of the post, (2) position of the post in the waveguide, and (3) applied d. c. magnetic field. Then, the T-equivalent circuits are obtained from the scattering matrix measurements. Results prove that when a thin ferrite post is placed near a side wall of the guide, it acts essentially as a shunting capacitance. The susceptance decreases with d. c. mangetic field. As far as the impedance is concerned, the post itself behaves like a tuning screw. Finally, the equivalent circuit of a waveguide containing two or more ferrite posts is studied. It is found that when the distance between the two nearest posts is greater then λ/2, the equivalent circuit is simply the 'single post' circuits connected in cascade. A phase shift network is used to illustrate the application of the principle of the circuit analysis.
This paper is intended to describe the properties of nonreciprocal microwave ferrite devices from the four-terminal network analysis. First, the impedance and the scattering matrix of an X-band rectangular waveguide containing a transversely magnetized ferrite post are measured as a function of the (1) diameter of the post, (2) position of the post in the waveguide, and (3) applied d. c. magnetic field. Then, the T-equivalent circuits are obtained from the scattering matrix measurements. Results prove that when a thin ferrite post is placed near a side wall of the guide, it acts essentially as a shunting capacitance. The susceptance decreases with d. c. mangetic field. As far as the impedance is concerned, the post itself behaves like a tuning screw. Finally, the equivalent circuit of a waveguide containing two or more ferrite posts is studied. It is found that when the distance between the two nearest posts is greater then λ/2, the equivalent circuit is simply the 'single post' circuits connected in cascade. A phase shift network is used to illustrate the application of the principle of the circuit analysis.
The multiplication and inhomogeneous nuckation of dislocations in silicon crystals have been studied under the actions of mechanical and thermal stresses by the chemical etching method. The experimental results indicate that for the production of multiplication and inhomogeneous nucleation of dislocations, thermal stress is equivalent to mechanical stress. Small-angle grain boundary dislocations, as well as individual as-grown dislocations, can act as dislocation sources. The stress concentration at the defects in the interior of the crystal and at the etch pits on the surface of the crystal can induce dislocation nucleation. Multiplication of screw dislocations may occur in the form of cross-glide. Studies of the spacial geometry of the newly-produced dislocation loops show that the Frank-Read mechanism is probably the primary form for dislocation multiplication.Whether a dislocation multiplies or not depends on the value of the resolved stress component acting on the dislocation source, the temperature and the structure characteristics of the dislocation itself, etc.
The multiplication and inhomogeneous nuckation of dislocations in silicon crystals have been studied under the actions of mechanical and thermal stresses by the chemical etching method. The experimental results indicate that for the production of multiplication and inhomogeneous nucleation of dislocations, thermal stress is equivalent to mechanical stress. Small-angle grain boundary dislocations, as well as individual as-grown dislocations, can act as dislocation sources. The stress concentration at the defects in the interior of the crystal and at the etch pits on the surface of the crystal can induce dislocation nucleation. Multiplication of screw dislocations may occur in the form of cross-glide. Studies of the spacial geometry of the newly-produced dislocation loops show that the Frank-Read mechanism is probably the primary form for dislocation multiplication.Whether a dislocation multiplies or not depends on the value of the resolved stress component acting on the dislocation source, the temperature and the structure characteristics of the dislocation itself, etc.