兼具高电流增益和高击穿性能的电荷等离子体双极晶体管

Bipolar Charge Plasma Transistor for High Gain and High Breakdown Performance

为了兼顾高电流增益β和发射极开路集电结的高击穿电压V_(CBO)与基极开路集电极-发射极间的高击穿电压V_(CEO),有效提升电荷等离子体双极晶体管(bipolar charge plasma transistor,BCPT)的高压大电流处理能力,利用SILVACO TCAD建立了npn型BCPT的器件模型。考虑到双极晶体管的击穿电压主要取决于集电区掺杂浓度,首先研究了集电极金属对BCPT性能的影响。分析表明,BCPT集电区的电子浓度强烈依赖于电极金属的功函数,当采用功函数较大的铝(Al)作为集电极金属时,由于减小了金属-半导体接触的功函数差,降低了集电区中诱导产生的电子等离子体浓度,从而有效降低了集电结空间电荷区峰值电场强度,减小了峰值电子温度以及峰值电子碰撞电离率,因此,达到改善击穿电压V_(CBO)和V_(CEO)的目的。然而,集电区电子浓度的减小会引起基区Kirk效应,增大基区复合,降低β。为此,进一步提出了一种采用衬底偏压结构的BCPT,通过在发射区和基区下方引入正衬底偏压,调制发射区和基区有效载流子浓度,达到提高发射结注入效率、增大β的目的。结果表明:与仅采用锆(Zr)作为集电极金属的BCPT相比,该器件的峰值电流增益改善了21.69%,击穿电压V_(CBO)和V_(CEO)分别改善了12.78%和56.41%,从而有效扩展了BCPT的高功率应用范围。

To enhance the high voltage and high current handling capacity of bipolar charge plasma transistor(BCPT),a device model of npn BCPT was established by SILVACO TCAD for balancing high current gainβ,high breakdown voltage of collector junction with emitter open V_(CBO)and high breakdown voltage of collector and emitter with base open V_(CEO).Considering that the breakdown voltage of bipolar transistors depends mainly on the doping concentration of the collector,the influence of collector metal on the performance of BCPT was firstly studied.It is shown that the collector electron concentration of BCPT depends strongly on the work function of the electrode metal.When aluminum(Al)with a larger work function is adopted as the collector electrode metal,the concentration of electron plasma induced in the collector region is reduced due to the decrease of work function difference between the metal and semiconductor contact.As a result,the peak electric field in the space charge region of the collector is reduced effectively,and the peak electron temperature and the peak electron impact ionization rate are also reduced,which leads to the improvements of the breakdown voltage V_(CBO)and V_(CEO).However,a decrease of electron concentration in collector will cause the Kirk effect in base,which will increase base recombination and lead to the decrease ofβ.Therefore,a structure of BCPT with substrate bias was proposed,where the positive substrate bias was adopted underneath the emitter and base to modulate the effective carrier concentration for increasing the efficiency of emitter junction injection and theβ.Results show that when compared with BCPT with zirconium(Zr)as collector metal,the peak value ofβof the BCPT is improved by 21.69%,and both of the breakdown voltage V_(CBO)and V_(CEO)are improved by 12.78%and 56.41%,respectively,which effectively expands the high power application range of BCPT.