5. If the avalanche breakdown occurs in a small part of the PN junction, the rapidly increasing current will be concentrated in this area, which will be burned down due to the concentration of heat. This destructive breakdown is called thermal breakdown, which is irreversible. This is mostly due to the uneven surface or residual mechanical damage of PN junctions.

6. Surface ions contaminate negative charges and repel electrons to attract holes, forming P-type inverted layer channels, thus increasing leakage current; while positive charges attract electrons to repel holes, which is equivalent to reducing surface resistivity, narrowing surface space charge region and forming low breakdown on PN junction surface.

7. When the surface of PN junction only produces the effect of current, the waveform is still avalanche breakdown, and VB is basically unchanged. Generating current I = qGXmS, S is the surface area of PN junction. Therefore, inadequate corrosion, rough surface, a large number of composite centers, make the surface leakage current larger.

8. Cleaning treatment before and after diffusion and cleanliness of diffusion system itself have great influence on voltage. Soft properties are related to the entry of harmful impurities into the body, so all kinds of contamination should be avoided.

9. Control of junction depth: A breakdown voltage requires the base region to exceed the width of the maximum space charge region; deep junction is easy to manufacture high-voltage device B current capacity requirements, VF can not exceed the standard C switching speed requirements. The wider the base area, the slower the speed.

10. The decrease of minority carrier lifetime is mainly caused by heavy metal impurities (copper, iron, nickel, lead, zinc, etc.) forming strong recombination centers. In addition to the silicon wafer itself, process operation, chemical reagents and utensils will bring heavy metal impurities. In addition, diffusion furnace tube wall is also an important, sometimes even the most important source. There are also a lot of alkali metals, alkaline earth metals and some excessive rare earth elements in the tube wall. They can penetrate the quartz tube wall and enter the tube from the quartz crystal gap. They not only pollute the silicon wafer, but also disintegrate the quartz tube (from transparency to whitening, crispening, peeling!).