Study OF Ultra-High Speed Heterojunction Bipolar Transistors with a Heavily Carbon-Doped Base

异质结双极晶体管作为一种高速器件受到了广泛的关注。本研究强烈提出，为了进一步提高HBTs的器件性能，降低基极电阻是非常重要的。也就是说，具有良好底掺杂约束的重掺杂基层是实现高速HBTs的关键结构参数之一。从这些角度出发，通过求解基本器件方程和hybrid-pi型等效电路模型，研究了降低基极电阻对超高掺杂InGaP/GaAs HBTs静态和动态特性的影响。通过将基孔浓度提高到1.5x10^<21>cm^<-3>，假设少数载波寿命gamma_n为10-100ps，估计电流增益大于10，并预测电流增益截止频率f_T为110 GHz，最大振荡频率f_<max>为160 GHz。在SPICE仿真器上研究了该器件的开关特性，在该器件结构下，可实现1 ps/栅极的传输延迟时间小于1 p / p>。基于此，采用新型晶体生长技术——金属有机分子束外延（MOMBE），开发了重杂质掺杂技术。碳(C)以其优异的稳定性和重掺杂能力，取代了传统的铍（Be）和锌（Zn）等p型掺杂剂在HBTs基层中的应用。以三甲基镓（TMG）为基材，采用MOMBE制备了重碳掺杂的p型GaAs和InGaAs，并对其碳掺杂特性、电学、光学和结构性能进行了详细研究。此外，由于InGaP和InP等磷化材料具有低表面复合速度的趋势，本研究还提出了作为新型HBTs发射极材料的InGaP和InP等磷化材料，并研究了这些化合物与新型金属有机磷前驱体叔丁基膦（TBP）的MOMBE生长。在高质量材料的生长过程中，与简单热解相比，裂化池内加热钽（Ta）的催化作用对于有效分解TBP至关重要。用裂解Si_2H_6研究了适合HBT应用的In_<0.5>Ga_<0.5>P中si掺杂的可控性。在MOMBE与TBP生长InP的过程中，发现TBP中的碳被吸收并作为活化良好的供体。结合这些MOMBE生长技术，在世界上首次提出并制备了掺杂碳的n型InP发射极和掺杂碳的p型InGaAs基底的InP/InGaAs HBTs。在共发射极静态特性方面，对于发射极面积A_E为80*80mum^2的器件，在集电极电流密度J_C为0.15kA/cm^2时，共发射极击穿电压BV_<CEO> >大于6 V，信号电流增益h_<fe> >为20，直流电流增益h_<fe>为11。此外，首次实现了具有超高碳掺杂基底的InGaP/GaAs HBTs，其空穴浓度为10^<21>cm^<-3>数量级。通过使用这种器件结构，人们强烈期望提高高频性能，因为基极中的超高掺杂可以极大地降低基极电阻。实际上，对于基底厚度为15 nm的器件，h_<fe>为16，h_<fe>为12。在可靠性测量中，在所调查的范围内未观察到电流增益的显著退化，表明碳作为p型掺杂剂具有完美的稳定性。综上所述，具有独特原始结构的HBTs的成功实现；首次研究了碳掺杂Inp发射极和碳掺杂InGaAs基底的Inp/InGaAs HBTs和超高碳掺杂基底（p=1.5 × 10^<21>cm^<-3>）的InGap/GaAs HBTs。少

Heterojunction bipolar transistors (HBTs) have attracted much attention as high-speed devices. In this research, it was strongly proposed that for further improved device performance of HBTs, reduction of base resistance is greatly important. In other words, heavily doped base layr with the well-confined base dopant is one of key structural parameters for realizing high-speed HBTs.From these points, effects of reduced base resistance on static and dynamic characteristics of InGaP/GaAs HBTs with an ultra-high doped base were studied by solving the basic device equations and the hybrid-pi type equivalent circuit model. By increasing the base hole concentration to 1.5x10^<21>cm^<-3>, current gains were estimated to be over 10 by assuming the minority carrier lifetime gamma_n of 10-100ps, and current-gain cutoff frequency f_T of 110 GHz and maximum oscillation frequency f_<max> of 160 GHz were predicted. Switching characteristics were also studied by using a SPICE simulator, and propagatio … More n delay time t_<pd> of l ps/gate was achieved in that device structures.Based on this consideration, heavy impurity-doping technique is developed by using novel crystal growth technique : metalorganic molecular beam epitaxy (MOMBE) . Instead of conventional p-type dopants such as beryllium (Be) and zinc (Zn) for base layr in HBTs, carbon (C) is proposed as a novel base dopant because of excellent stability and capability of heavy doping. Heavily carbon-doped p-type GaAs and InGaAs were developed as base materials by MOMBE with trimethylgallium (TMG) , and carbon-doping characteristics and electrical, optical and structural properties were studied in detail. Furthermore, phosphide materials such as InGaP and InP are also proposed in this research as novel emitter materials of the HBTs because of the tendency of low surface recombination velocity, and MOMBE growth of these compounds is investigated with new metalorganic phosphorus precursor : tertiarybutylphosphine (TBP) .In the growth of high quality materials, the catalysis by means of heated tantalum (Ta) inside the cracking cell was important to effectively decompose the TBP as compared to simple pyrolysis. Controllability of Si-doping in In_<0.5>Ga_<0.5>P suitable for HBT application was also studied by using cracked Si_2H_6. In the growth of InP by MOMBE with TBP,it was revealed that carbon from the TBP is incorporated and acts as well-activated donor.By combining these MOMBE growth techniques, InP/InGaAs HBTs with carbon-doped n-type InP emitter and carbon-doped p-type InGaAs base are proposed and fabricated for the first time in the world. In common-emitter static characteristics, relatively large commonemitter breakdown voltage BV_<CEO>above 6 V was achieved, and small signal current gain h_<fe> of 20 and d.c.current gain h_<FE> of 11 were obtained at collector current density J_C of 0.15kA/cm^2 for a device with emitter area A_E of 80*80mum^2.Furthermore, InGaP/GaAs HBTs having an ultrahigh carbon-doped base with a hole concentration of the order of 10^<21>cm^<-3> are realized for the first time. By using that device structure, improved high-frequency performance is strongly expected because base resistance could be extremely decreased due to the ultra-high doping in the base. In fact, h_<fe> of 16 and h_<FE> of 12 were obtained for devices with a base thickness of 15 nm. In the reliability measurements, a significant degradation of current gain was not observed in the range investigated, indicating a perfect stability of carbon as a p-type dopant. In conclusions, successful realization of HBTs with unique original structures ; Inp/InGaAs HBTs with carbon-doped InP emitter and carbondoped InGaAs base and InGap/GaAs HBTs with an ultra-high carbon-doped base (p=1.5*10^<21>cm^<-3>) , was studied for the first time. Less