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对N型硅MOS二极管的栅极施加大的负电压时,硅表面可出现反型层。但是,支配这个过程的时间常数大约是0.1～1秒。如果所加的负向电压采用脉冲形式,脉冲的幅度足够大,脉冲的持续时间与少子的热产生时间常数比较又很短,则半导体表面将不会形成反型层,而是形成一个宽的空间电荷层。随着电压幅度增大,硅表面层的电场增强。当脉冲电压的幅度大到使表面上的电场达到雪崩电场E_(?)时,发生雪崩效应。外加脉冲电压V_A、雪崩电场E_(?)和击穿表面势ψ_((?)a)间的关系可由泊松方程得到:
When a large negative voltage is applied to the gate of an N-type silicon MOS diode, an inversion layer may appear on the silicon surface. However, the time constant governing this process is about 0.1 to 1 second. If the applied negative voltage is in the form of a pulse, the amplitude of the pulse is large enough, and the duration of the pulse is short compared to the heat generation time constant of a few, the semiconductor surface will not form an inversion layer but a wide Space charge layer. As the voltage amplitude increases, the electric field of the silicon surface layer increases. The avalanche effect occurs when the pulse voltage is so large that the electric field on the surface reaches the avalanche E_ (?). The impulse voltage V_A, the avalanche electric field E_ (?) And the breakdown surface potential ψ_ ((?) A) can be obtained from the Poisson equation: