[研究生入學(xué)考試]20xx-20xxchapter-展示頁
2025-03-30 22:13本頁面
【正文】 xcitation with light h?Eg hole injection device: Inject holes at predetermined rate into the n side of the junction. The current from n to p will depend on the hole injection rate, and will be essentially independent of the bias voltage A convenient hole injection device is a forwardbiased p+n junction. In p+n junction, the current is due primarily to holes injected from the p+ into the n region. If we make use of the same n side for both forward and reversebiased junction, we can obtain the p+np structure. In this structure, injection of holes from p+n junction into the n region supplies the minority carrier holes to participate in the reverse current through the np junction. To enable the p+np structure to normally operate, it is important that the injected holes do not rebine in the n region before they can diffuse to the depletion layer of the reverse biased junction. So, we must make the n region narrower than the hole diffusion length, WbLp. forwardbiased reversebiased (1) Injected holes lost to rebination in the base (2) Holes reaching the reversebiased collector junction (3) Thermally generated electrons and holes making up the reverse saturation current of the collector junction (4) Electrons supplied by the base contact for rebination with holes (5) Electrons injected across the forwardbiased emitter junction The base current originates from the following three mechanisms: ?There must be some rebination of injected holes with electrons in the base, even with WbLp. The electrons lost to rebination must be resupplied through the base contact. ?Some electrons will be injected from n to p in the forward biased emitter junction, even if the emitter is heavily doped pared to the base. These electrons must also be supplied by IB. ?Some electrons are swept into the base at the reversebiased collector junction due to thermal generation in the collector. This small current reduces IB by supplying electrons to the base. Amplification with BJT ?Some assumption : (1)Neglecting the saturation current
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