Theoretical and experimental investigations are made of the photoconductivity in anisotropically deformed germanium in conditions favourable to the occurrence for electrical pinch. A saturation of the photocurrent for sufficiently high electric fields is predicted and observed. The effect of the electric field on the spatial distribution of the carriers in an illuminated crystal is investigated using the infrared spot method. Similar values of the surface recombination velocities are obtained from the current‐voltage and relaxation characteristics.
A new possible mechanism is proposed for explaining the high photovoltage arising in semiconductor films assuming an anisotropic conductivity of the photosensitive crystallites of which the films consist. In this case the high photovoltage is the sum of the elementary transverse Dember photo-e.m.f.'s. This model may explain practically all peculiarities of the high-photovoltage effect.
The phenomena accompanying the flow of an electric current through uniaxially compressed plates of intrinsic Ge are investigated. The plates are cut with definite orientations relative to the main crystallographic axes so that the directions of the current and field do not coincide. Under these conditions transverse gradients of the nonequilibrium carrier concentration arise in specimens long carrier lifetimes, this results in a modulation of the conductivity, emergence of rectifying characteristics, etc. In strong field the carriers and current are concentrated in a narrow layer close to one of surfaces, the carriers being almost completely removed from the rest of the specimen (the electrical pinch in an electron‐hole plasma). The redistribution of carriers across the sample and the current‐voltage characteristics are investigated experimentally for these pinch conditions. For fields of about 100 V/cm an increase and decrease of concentration is observed, giving an extremely nonlinear current‐voltage characteristic if opposite plate surfaces have different surface recombination velocities. A rectification ratio of about 50 may be obtained in this way. Under electrical pinch conditions the dependence of the resistance of the specimen on compression exceeds the ordinary piezoresistance by an order of magnitude.
Theoretical and experimental investigations of the conductivity of elastically bent intrinsic Ge are performed. An high asymmetry of the current-voltage characteristir is predicted and observed in plates with a high velocity of surface recombination. It is connected with the deviation of the spatial distribution of carriers for two opposite directions of current, flowing through the crystal. It is shown that a negative differentia1 resistance in thin crystals may arise a t great electrical fields. Current oscillations connected with the Joule heating of the specimen are observed.
The anisotropic deformation of germanium crystals results in an anisotropy of electron and hole mobilities. In the case of uniaxial compression (or tension) of a germanium plate the anisotropic flow sweeps carriers on one of the plate surfaces, where an enhanced recombination takes place. In this case the effective lifetime decreases inversely proportional to the electric field in the plate (1, 2).At bend deformation the sign of anisotropy is not the same for both sides of the plate. Therefore injected carriers are sweept from the volume on both surfaces at one direction of bend (inverse bend) and are concentrated near the neutral plane of the plate at another direction (direct bend) (3). At the inverse bend the effective lifetime of injected carriers changes inversely proportional to the electric field, as before, while the direct bend results in increasing of lifetime up to its bulk value.The electric field distribution in plate-shaped diodes is inhomogeneous at high + + injection level. If both electrodes inject nonequilibrium carriers (p -n-n diode) the field is maximum near the middle of the interelectrode distance and is small near the electrodes. Therefore the intensity of the electric field is sufficient for a substantial change of the effective lifetime in the region only near the middle of a diode; the length of this region increases with the increase of the deformation.In the case of inverse bend the carrier concentration in this region saturates with the voltage increase on the diode. A s a result the volt-ampere characteristic, which is determined by the voltage drop in this region, must be ohmic. The resistance of the diode must be the greater, the greater the value of the inverse bend is.At direct bend the effective lifetime of carriers in the mentioned region reaches its bulk value. This results in a decrease of the effective diode length (the latter is 1) It is." kT/eLe, where Le is the effective diffusion length.
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