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编辑部转来了读者来信,提出的问题,很有代表性。一年多来,我们对所谓“自隔离”现象又有一点新的认识,为了共同讨论,我们再谈一谈对这一问题的看法。由于缺少测试条件,认识仍然是很不深刻的,缺点和错误在所难免,希望批评指正。1、“外延自隔离”的本质关于这一现象的本质我们曾经谈过一点看法,通过最近我们所作的实验,和我们所了解的情况来看,仍然认为,所谓“自隔离”实际上并不是真正的隔离,而是在外延层电阻率很高、厚度又较薄时在加适当的偏压下耗尽层扩展的结果。根据上海元件五厂和复旦大学的测量发现,在不掺杂时,外延层是N型30Ω.cm,墙区PN结零偏势垒宽度即达3微米,稍加偏压,势垒就会扩展得很宽,可以将外延层夹断。电阻率越高,“夹断电压”就越低,夹断后的饱和电流也就越小。当电阻率足够高,而外延层又
The editorial department turned to the letter from the reader, put forward the question, very representative. In the past year or so, we have a new understanding of the so-called phenomenon of “self-isolation.” For the purpose of joint discussion, we will again talk about this issue. Due to the lack of testing conditions, knowledge is still not very profound, shortcomings and errors are inevitable, I hope criticism. 1. The Essence of “Denoting Self-isolation” As for the nature of this phenomenon, we have already talked about some points of view. From the recent experiments we conducted and what we know, we still think that the so-called “self-isolation” is not actually True isolation, but rather the result of depletion of the depletion layer at the appropriate bias voltage with high resistivity of the epitaxial layer and thinner thickness. According to the survey conducted by Shanghai No.5 Factory and Fudan University, the epitaxial layer is N-type 30Ω.cm without doping. The width of the PN junction zero-bias barrier in the wall area is 3 μm. With a slight bias voltage, the barrier will be Extend very wide, you can pinch off the epitaxial layer. The higher the resistivity, the lower the “pinch-off voltage” and the smaller the pinch-off saturation current. When the resistivity is high enough, the epitaxial layer again