Minority carrier injection in relaxation semiconductors under illumination

The paper considers the injection of minority carriers into a relaxation semiconductor under uniform illumination. Steady state solutions have been computed, and used to assess the nature of the recovery process after cessation of the light. It is concluded that measurements of photoconductive decay do not in general lead to reliable lifetime estimates because, besides recombination, the movement of space charges is involved in the recovery.     

The concept of screening length in lifetime and relaxation semiconductors

It is shown that, contrary to normal practice, the most appropriate criterion for distinguishing between lifetime and relaxation semiconductors in the presence of traps is the ratio of the screening length L_s, to the ambipolar diffusion length L_Da,. L_s, is calculated. Its significance is not limited to zero current, even though it reduces to the conventional Debye length L_D when the trap concentration is zero. (With traps, we always have L_s < L_D.) The dielectric relaxation time itself is unaffected by traps, but in steady state situations, a material behaves as if it had an effective lifetime τ_0s = τ₀η, where η depends on the concentration and energetic position of the traps. τ_o, may be orders of magnitude greater than τ₀, the conventional diffusion length lifetime. Typical values of L_s, are presented as a function of trapping parameters. L_s>L_Da leads to relaxation behavior; L_s < L_Da, to lifetime behavior.     

Threshold switching characteristics

The paper describes experiments on thresholds switches, based on a multicomponent chalcogenide glass (Te₄₀As₃₅Ge₇Si₁₈) of about 1 μm thickness, and pyrolytic graphite electrodes. The results demonstrate that “forming processes” (of presumably electrolytic character) in the off-state affect only the contact area which is not engaged in filamentary conduction when the switch is in the on-state. The detailed on-state characteristics are shown to depend on (a) the maximum on-current reached during the switching event, and (b) the rate of voltage change, and this is why depend on the external series resistance. Forming processes in the on-state must arise from a very different mechanism, and the operational reality of the minimum holding current has been established. The resultsfavor non-thermal interpretations of threshold switching as such, albeit inevitably with certain “thermal overtones”.     

On the gelling of sodium metasilicate solutions

Summary Experiments are described which suggest strongly that the gelling of sodium metasilicate solutions is dependent on foreign trace additives. Gelling can be inhibited by their removal, achieved by a simple process which has been called “gel gettering”. Also affiliated with the Department of Physics.     

ChemInform Abstract: On Compound Formation of M′O:M2O3. Part 11. Crystal Structure of BaIn2O4.

Single crystals of the title compound, obtained from a melt after reacting intimate mixtures of BaCO₃ and In₂O₃ at 840 °C (12 h), belong to the monoclinic space group P2₁/a with Z=16.     

ChemInform Abstract: Boron Occupied Condensed Clusters in Ta5Ge3By (y ≈ 0.7).

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