Currents In Semiconductors Research Articles

Theory of beam-induced currents in semiconductors

An analytical model is presented for the current flowing in a Schottky diode or shallow p-n junction when the current is generated by an electron beam or light beam. The model represents an exact solution to the three-dimensional diffusion equation when the current-collecting junction is at right angles to a grain boundary or to the semiconductor surface. The finite size of the electron-hole generation region is readily included in the analysis. The results are given in terms of one-dimensional integrals which can simply and accurately be evaluated using a programmable hand calculator. The theory provides a basis for using electron-beam-induced currents or light-beam-induced currents to measure the minority-carrier diffusion length and surface recombination velocity at a grain boundary or surface.

Injected carrier lifetimes and double-injection currents in semiconductors with a single impurity level

Theoretical analyses of the lifetimes of injected electrons and holes, and the double-injection currents in long p-i-n diodes with a single impurity level, are treated by evaluating the space-charge density formed by the injection of the minority carrier lifetimes and the current-voltage characteristics are obtained in a low- and a high-injection regime, and approximately in an intermediate-injection regime, when the physical parameters of the i region and the dependence of the equilibrium majority-carrier density upon temperature have been measured beforehand.

The interpretation of space-charge-limited currents in semiconductors and insulators

The specific current-voltage-temperature dependence of space-charge-limited conduction processes in semiconductors and insulators is largely determined by the distribution in energy of traps within the band gap. A linear dependence of current-density on the square of the applied voltage, may be alternatively interpreted in terms of either a single discrete trapping level, or of an exponential trap distribution. The two types of trapping behavior may be distinguished using measurements of the variation of current with temperature for a range of different constant voltages.

Electron-Beam-Induced Currents in Semiconductors

The scanning electron microscope (SEM) is an extremely versatile instru­ ment capable of yielding many different kinds of information from the resulting interaction of the electron beam and the sample. One such interaction produces currents in semiconductors, the topic of interest here. The popular acronym for this subject is EBIC (electron-beam­ induced current). The EBIC technique can, among other things, be used to directly image recombination sites; to measure transport properties such as minority carrier diffusion length, lifetime, and surface recombina­ tion velocity; to determine junction depths and shallow trap energy levels; to image inversion layers in integrated circuits; and to map leakage paths and microplasma sites. There exists in the literature, however, a lack of clarity regarding the interpretation and basic accuracy of some of the above measurements. Our aim in this article is therefore twofold: to clarify this situation through reviewing the limits and applica­ bility of the various models, and to explain the technique itself and discuss examples of its application, power, and limitation.

Collisionless space-charge limited currents in semiconductors with nonparabolic bands

The current-voltage relation for space-charge limited collisionless flow is computed for a model semiconductor with a hyperbolic band structure as deduced from two-band <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\bar{k} \cdot \bar{p}</tex> perturbation theory. The expected current is reduced significantly below the constant effective mass value for voltages in excess of the bandgap, and the high-voltage asymptotic relation is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</tex> rather than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V^{3/2}</tex> .

The influence of carrier capture in deep traps on the small-signal characteristics of double-injection currents in semiconductors

A calculation of a p-n-n+ structure small-signal impedance with high injection level is carried out taking into account the capture of carriers in deep traps. The impedance is calculated for the case of weak occupancy of the traps. For the two extreme cases corresponding to small and high rate of the leakage of carriers through the junctions as compared to the rate of their recombination in the n-base, the active and reactive components of the impedance of a long diode (w ≧ 3L), the inductive reactance Q-factor as functions of the current jo, the alternating signal frequency w, and the parameters of trapping centres are analyzed. The results obtained are compared with experimental data on the small-signal impedance of planar gold-doped silicon diodes. [Russian Text Ignored]

Thermally Stimulated Currents in Semiconductors and Insulators Having Arbitrary Trap Distributions

The theory is developed for thermally stimulated currents (TSC) that flow in optically or electrically excited insulators and semiconductors in which the field is sufficiently high and the (active) region in which the free carriers are generated is sufficiently thin (e.g., reverse-biased junctions, thin films, etc.) so that recombination rate of the free carriers is negligible. Closed-form solutions are obtained for the TSC characteristics for semiconductors and insulators containing arbitrary trap distributions. Using various ad hoc trapping distributions, it is shown that the approximate high-field TSC characteristics correlate extremely well with the exact characteristics that were computed numerically. More important, however, it is shown that the shape of the observed TSC characteristic is a direct reflection of the sum of the trap distribution in the upper half and the lower half of the band gap. The technique is potentially a powerful means of characterizing trap distributions in defect semiconductors and insulators, in that it permits the direct determination of the trap distribution without requiring an a priori knowledge of the trap parameters and without the need for laborious analyses.

On the theory of injection currents in semiconductors with deep traps

Effect of the ambipolar mobility variation on the double injection is investigated for the compensated semiconductors with deep single-level traps in the case where the lifetime variation is weak on the average in the sample and quasineutrality approximation can be used. The conditions are found under which the negative resistance (NR) arises due to the increase of the ambipolar mobility and the lifetime in a long sample. The mechanism of the appearance of the NR in the bulk of the relatively short samples is discussed. NR arises because of the increase of the effective length of the injected carrier penetration into the sample due to joint action of the diffusion and of the ambipolar drift. [Russian Text Ignored]

Ambipolar mobility and injection currents in semiconductors with deep traps

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