Life-time semiconductor

The counterpart to Fig. 5.95, namely the situation of a p-n junction in equilibrium (e.g. contact of donor-doped and acceptor-doped Si) is illustrated in Fig. 5.113. Marked, rectifying properties of such junctions occur primarily in life-time semiconductors . In view of the extensive literature on this subject, we will not go in any finther detail here. 

After the absorption of a photon sufficiently close to the semiconductor/ electrolyte interface, primary separation of the electron and hole will occur. The minority carrier (hole) may diffuse to the inner edge of the depletion layer, and migrate through the depletion layer towards the surface. Diffusion occurs in a time equal to the life time of the minority carrier in the bulk, t, which for compound semiconductors is often in the microsecond or nanosecond range (in very pure Si, the minority carrier life time is much larger (ms) [158]). In section 2.2, it was shown that... 

Important reasons for not applying polysilanes are probably the difficulties in controlling their synthesis with regard to molecular weight, PDI and impurities as well as the high costs of these elaborate methods and the purification processes involved. Additionally, there is little known about polysilane degradation and, thus, life time shortening in semiconductor devices. This in turn may be due to the limited supply of structurally diverse polysilanes accessible by the routes known. 

The band edges are flattened when the anode is illuminated, the Fermi level rises, and the electrode potential shifts in the negative direction. As a result, a potential difference which amounts to about 0.6 to 0.8 V develops between the semiconductor and metal electrode. When the external circuit is closed over some load R, the electrons produced by illumination in the conduction band of the semiconductor electrode will flow through the external circuit to the metal electrode, where they are consumed in the cathodic reaction. Holes from the valence band of the semiconductor electrode at the same time are directly absorbed by the anodic reaction. Therefore, a steady electrical current arises in the system, and the energy of this current can be utilized in the external circuit. In such devices, the solar-to-electrical energy conversion efficiency is as high as 5 to 10%. Unfortunately, their operating life is restricted by the low corrosion resistance of semiconductor electrodes. 

The degree of activation of the sample is measured by post-irradiation spectroscopy, usually performed with high-purity semiconductors. The time-resolved intensity measurements of one of the several spectral lines enables to get the half-life of the radioactive element and the total number of nuclear reactions occurred. In fact, the intensity of a given spectral line associated with the decay of the radioactive elements decreases with time as Aft) = Aoexp[—t/r], where Aq indicates the initial number of nuclei (at t = 0) and r is the decay time constant related to the element half-life (r = In2/ /2), which can be measured. Integrating this relation from t = 0 to the total acquisition time, and weighting it with the detector efficiency and natural abundance lines, the total number of reactions N can be derived. Then, if one compares this number with the value obtained from the convolution of... 

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