A Numerical Study of a New Four-layer-substrate Closing Device Tara afra 1 , Seyed Nasrolah Anousheh 2 , Ahmad Taghinia 4 Electrical Engineering Department Islamic Azad University 1 South Tehran Branch 2,4 CentralTehran branch Tehran, Iran t.afra84@yahoo.com s.n.anousheh@gmail.com Morteza Fathipour 3 Device Modeling and Simulation Lab Tehran university Tehran,iran Mfathi@ut.ac.ir Abstract— Creating high power electrical pulses with sub nanosecond rise time is possible by using fast impact ionization process in closing four-layer-substrate devices. Fast impact ionization in semiconductor devices is one of the quickest non- optical pulse generation methods even in the range of less than nanosecond. In this paper electron-hole plasma generation and fast impact ionization mechanism of a four-layer-substrate device would be discussed by using numerical study and also physical model, Effective factors such as impurity concentration and substrate thickness in switching velocity, current peak, generated electron-hole plasma and residual voltage in device . This study provides several optimized characteristics in these switches. I. INTRODUCTION In many applications including in air plasma generator transmitters [1], vacuum electronic device driving stages, power lasers and accelerators [2] , usage of High power nanosecond pulses are needed. New method of pulsed power is developed on the basis of new effect in high voltage semiconductor p-n junction. This effect has been used to design closing switches-Fast Ionization Dynistor with nanosecond and even Sub nanosecond risetime operating. Voltages of 3-10 KV for a single p-n junction [3]- [7]. With proper triggering circuits one can construct a pulse generator with low jitter. Other advantages are compact size and light weight. In typical of semiconductor devices, Fast Ionization Dynistor ,have very long lifetimes. Fast Impact ionization process in semiconductor devices is known as one of the fastest non-optical approach to produce nanosecond and high power pulses [6]-[10] Using above mentioned approach, plasma i.e. [10] an aggregation of negative electrons and positive holes charges next to each other distributes in the base of p+ N p n+ with a velocity several times larger than saturation velocity. Thus dynistor turns on in a very short time. Under this situation dynistor provides a high amount of current. Despite high current capability in these switches, their short coming is that main electric field, cannot be completely eliminated in the base of such devices this phenomenon finally results in a residual voltage. Next, the process of plasma generation and impact ionization in such devices is numerically analyzed.We then discuss effective parameters which affect plasma concentration and maximum output current and also residual voltage. Finally a conclusion is provided. II. WAFER PROPERTIES AND IMPURITY CONCENTRATION Semiconductor closing switches employ a p+ N p n+ structure of approximately 350 um width with a dopant distribution similar to that shown in figure 1. Figure 1. Device impurity structure