摘要:

Data on ac and dc field dependence of the conductivity of semi‐insulating GaAs crystals are reported. The existence of long‐range potential fluctuations in these samples has been previously reported. Field‐enhanced conductivity results from the decrease of the maximum depth of the wells due to barrier lowering, up to a critical field at which the effect of potential fluctuations disappears. The transient behavior is also discussed.

ISSN:0021-8979    

DOI:10.1063/1.337398

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The analytical expression is derived for the time dependence of the total minority‐carrier content in a semi‐infinite semiconductor slab, after excitation with a delta function light pulse. It is shown that to this end it is sufficient to solve the continuity equation for the minority carriers in one dimension only. This implies that the excitation may have an arbitrary lateral spatial distribution. The photoluminescence, probing the total minority‐carrier content, turns out to be a nonexponential function of time when the surface/interface recombination velocity differs from zero. A practical method is developed to deduce accurate values of the bulk lifetime and the interface recombination velocity from such a nonexponential decay curve, based on a special way of plotting. Moreover, the analytical expressions are derived for the photoluminescence decay in the case of finite slab thicknesses and finite interface recombination velocities. From these results it is evident that only for large ratios (>10) of slab thickness and minority‐carrier diffusion length can the semiconductor be considered as being semi‐infinite.

ISSN:0021-8979    

DOI:10.1063/1.337399

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Magnetoresistance skewness effect (change of the principal directions of electrical resistivity) appears when a magnetic field of arbitrary direction is applied on the examined material. This effect is useful for the magnetoresistance coefficients determination. A complete investigation of the skewness effect requires additional experimental facilities, such as the rotation of the sample and the contact system, which in some cases are impossible or very difficult to obtain. In this work the importance of the (110) and (111) planes of cubic crystals for such measurements is shown. For this purpose the elements of the resistivity tensor in the systems of reference, used in these planes, are correlated with those in the basic system of the (001) plane.

ISSN:0021-8979    

DOI:10.1063/1.337400

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The resistivity of a commercial carbon‐filled composite conducting polymer (ET‐Semicon&squflg;) has been measured as a function of temperature between 80 and 400 K and under pressure up to 1.5 GPa (15 kbar). Large changes in resistivity were observed. The resistivity was also very sensitive to the presence of certain solvents and hydrocarbons. The results are explained as percolation effects caused by changes in volume due to pressure, thermal expansion, or dissolved solvents. The material studied is found to have a wide range of potential applications for pressure measurements and as a transducer for gas or liquid concentration.

ISSN:0021-8979    

DOI:10.1063/1.337401

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The conditions of strong surface inversion in the semiconductor surface of a metal‐insulator‐semiconductor (MIS) tunnel structure are studied. By employing the voltage equation which governs the potential distribution in the MIS diode and by defining a parameter &thgr; which indicates the energy separation between the semiconductor minority‐carrier quasi‐Fermi level and the metal Fermi level at the insulator–semiconductor interface, the values of &thgr;(inv)under strong surface inversion are calculated in terms of oxide thickness, metal work function, oxide and interface state charges, semiconductor doping concentration, and reverse bias voltage. There are three conditions, namely, (1) without the external injection of the minority‐carrier current densityJinj(i.e.,Jinj=0), (2) with it (i.e.,Jinjis positive), and (3) whereJinjis negative (i.e., carrier extraction). The second condition can be attributed to the critical insulator thicknessdcribelow which the semiconductor surface cannot be inverted solely by applying a reverse bias voltage, hence an externally injected minority‐carrier currentJinj(inv)is required to achieve strong surface inversion at certain bias and oxide thickness. It also reveals thatJinj(inv)increases with decreasing insulator layer thickness and is strongly dependent on the oxide and interface state charges. For the Al–SiO2–Si tunnel structure, the calculated value ofdcriis about 30 A˚, which is in good agreement with the reported experimental results of 28–35 A˚.

ISSN:0021-8979    

DOI:10.1063/1.337776

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

An equation for the residual current induced by electric potential during charging of the gate electrode in modified transistors was derived by using electrical conductivity, Atalla’s model, and Ihantola’s equation for metal‐oxide‐semiconductor devices. The equation was examined by comparing calculated values with measured values of the residual current in a transistor covered with a silicone elastomer vulcanized by various reactions. Factors causing variations in hardness affect the electrical conductivity of the silicone elastomers. These are analyzed based on the vulcanization reaction system and the catalyst species.

ISSN:0021-8979    

DOI:10.1063/1.337402

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Lateral diffusion of carriers in closely spaced photodiode arrays leads to image degradation. The effect is analyzed for backside illuminated arrays in the limiting cases of very small and very large optical absorption lengths. It is concluded that closely spaced two‐dimensional arrays for thermal imaging applications will require the use of semiconductors whose thicknesses are less than the diameters of the photodiodes.

ISSN:0021-8979    

DOI:10.1063/1.337403

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A modulation‐doped field‐effect transistor model for long‐channel devices is discussed and results presented. The model takes into account an arbitrary electrons degeneracy condition. It describes the drain current accounting for both the drift and the diffusion components in the constant mobility approximation. The additional effective electric field that arises due to dependence of the subband bottom on concentration is also taken into account. It is shown that at low temperatures (78 K) the degeneracy of the channel electrons plays an important role in the entire region of the device operation including the saturated region of theI‐Vcharacteristics.

ISSN:0021-8979    

DOI:10.1063/1.337351

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A construction method for determining the domain structure in ideally soft‐ferromagnetic cylindrical objects with plane‐parallel top and bottom surfaces of arbitrary shape is presented. The self‐consistent theory is confined to two‐dimensional solenoidal dipole distributions in which the dipoles are parallel to the top and bottom surfaces. It is proved that the basic domain structure is uniquely defined in simply connected objects, while an extra criterion has to be added in order to guarantee the uniqueness in the multiply connected ones. The treatment is based on differential geometrical principles. The object edge is partitioned into segments, in which each segment is situated in between two adjacent edge points where the radii of curvature of convex edge segments are locally minimal. To each edge segment, a region is attributed, in whichMis uniquely specified by the course ofMalong that edge segment. In the cross section of regions corresponding to different edge segments, domain walls provide an adequate separation of the dipole distribution imposed by these segments. The extremities of these domain walls are found in the singular points of the evolute corresponding to the extremities of the edge segments and in the points where a number of walls meet. It is proved that the basic domain structure is the locus of centers of all circles inside the object that touch the object edge at at least two points. A number of experimentally observed basic structures are given, and the relevance of the definition of basic structures in multiply connected objects is examined. OFF

ISSN:0021-8979    

DOI:10.1063/1.337352

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Trends in structural and magnetic parameters are presented and discussed for Nd2Fe14−xTxB with T=Cr, Mn, Co, Ni, Al. Some data are also included on the Y analog systems. Partial Al substitution strongly increasesc/a. We show that this has to do with preferential occupation of the larger atom (Al) in the &sgr;Fe layer. Co and Ni substitutions increase Curie temperature (TC) while all others decrease it. Anisotropy constantsKfor 300 K decrease in all cases investigated compared to Nd2Fe14B. Some discussion is given to the general mode of preferential substitution and the concomitant effects on magnetic anisotropy.

ISSN:0021-8979    

DOI:10.1063/1.337353

出版商:AIP    

年代:1986

数据来源: AIP