Gagan Khanduri

A study of the effects of the base doping profile on SiGe heterojunction bipolar transistor performance for all levels of injection

The effects of two different base doping profiles on the current gain and cut-off frequency for all levels of current injection have been studied for NPN Si/SiGe/Si double heterojunction bipolar transistors (SiGe DHBTs). The two-dimensional simulation results for a SiGe DHBT with uniform base doping and a fixed base Gummel number are compared with a non-uniform base doping profile SiGe drift-DHBT device. The study explains the performance of SiGe HBTs at different injection levels by analysing the electron and hole mobility, drift velocity, electric field, junction capacitances and intrinsic and extrinsic base region conductivities. The base doping profile in the SiGe drift-DHBT is controlled in such a way that it creates a net accelerating drift field in the quasi-neutral base for minority electrons. This accelerating field subsequently improves the current gain and cut-off frequency for the SiGe drift-DHBT in comparison with the SiGe DHBT for all levels of injection.

Simultaneous optimization of doping profile and Ge-dose in base in SiGe HBTs

This work presents an approach to optimize the base doping and Ge-dose inside the base of SiGe HBTs using the fixed point iterative methodology and includes the effect of minority carrier velocity saturation on total base transit time for SiGe HBTs. It is shown that shifted-Ge approach and linear Ge-profile in base can lead to simultaneous optimization of Ge-dose and base dopant distribution for minimum base transit time.

Optimization of Base Profile in Bipolar Transistors Considering Retarding Field in Base, Sheet Resistance and Minority Carrier Velocity Saturation

This work studies the effects of base retarding field, sheet resistance and minority carrier velocity saturation on base transit time for optimal base profile in bipolar devices. An iterative technique is employed to provide a global minimum for the product of transit time and sheet resistance in base. The global minimum in base transit time is achieved for optimum base doping profiles with uniform peak base-doping region extending over most part of base region till the point of deflation of doping concentration.

Base doping profile optimization including carriers velocity saturation effect

This work presents an iterative approach to optimize the base doping of conventional Si BJTs for practical base profiles having retarding field region near emitter-base junction. The analysis also presents the effect of minority carrier velocity saturation on total base transit time for homojunction bipolar transistors.

Analysis of base recombination effect in very high maximum oscillation frequency silicon-germanium heterojunction bipolar transistors

The performance for current gain (β) and cutoff frequency (∫ i) for very high maximum oscillation frequency (∫max) NPN Si/SiGe/Si Double Heterojunction Bipolar Transistors (SiGe DHBTs) has been analyzed. The simulation results for a conventional Box-Germanium (BT-GE) profile and a Box-Triangular-Germanium (BT-GE) profile are compared in the present work. The Ge profile is kept under the critical thickness limit constraint in both the cases, The BT-GE SiGe DHBT shows a superior current gain and cut-off frequency in comparison with B-GE DHBT. The analysis of the stated observation brings out the dominance of base region recombination in high ∫max SiGe HBTs, as the base resistance is reduced.

A novel approach for justification of box-triangular germanium profile in SiGe HBTs

This work presents a unique and robust approach for validation of using the box-triangular germanium profile in the base of SiGe heterojunction bipolar transistors, where the methodology considers the simultaneous optimization of the p-type base doping profile in conjunction with the germanium profile in the base. The study analyses the electron motion across the SiGe base in SiGe HBTs, owing to different accelerating electric fields. The analysis first presents a figure of merit, to achieve the minimum electron transit time across the base in conjunction with the increased current gain in n—p—n-SiGe HBTs, which shows a general trend vis-a-vis the advantage of a trapezoid germanium profile, but with additional accuracy as we considered simultaneously optimized p-type base doping. The effect of minority carrier velocity saturation is then included to make the study more detailed. The analysis then investigates the shifted germanium profile in the base to further minimize the base transit time. Finally, it is shown that a shifted germanium profile eventually evolves into a box-triangular Ge-profile in the SiGe base, which could simultaneously minimize the base transit time and reduce emitter delay by virtue of the high current gain. The analysis verifies that for an average Ge-dose of 7.5% Ge across the base, a box-triangular germanium profile in conjunction with an optimum base doping profile has an approximately identical base transit time and a 30% higher current gain, in comparison with an optimum base doping and triangular Ge-profile across the whole base.

Current gain modeling of SiGe DHBTs in SPICE including retarding potential barrier effect

This paper presents an approach to model the current gain in SiGe DHBTs, by using the fitting coefficients to modify the model parameters of Si BJTs in OrCAD PSPICE. The effect of dynamic retarding potential barrier at base-collector heterojunction in SiGe DHBTs is also modeled by using a resistor in parallel with internal base resistance RB.

Optimization of Ge-Dose and Doping in Base of SiGe HBTs

The present work gives an approach to optimize the base doping and Ge-dose in SiGe HBTs using the fixed point iterative methodology and includes the effect of minority carrier velocity saturation on total base transit time for SiGe HBTs. It is shown that shifted-Ge profile approach and triangular Ge-profile in base can lead to simultaneous optimization of Ge-dose and base dopant distribution for minimum base transit time.

An Iteration Approach for Optimization of Base Doping Profile in Si BJTs

The paper presents an iterative scheme for optimizing the practical base doping profiles of conventional Si BJTs to minimize its base transit time. The analysis also provides the effect of minority carrier velocity saturation on total base transit time for homojunction bipolar transistors.

Base doping profile effect in SiGe heterojunction bipolar transistors

The current gain and cut-off frequency performance in NPN Si/SiGe/Si double-heterojunction bipolar transistors (SiGe DHBTs) with two different base doping profiles (N/sub B/) has been analyzed. The simulation results for conventional uniform-N/sub B/ SiGe DHBT are compared with the proposed SiGe drift-DHBT (DrDHBT) having N/sub B/-ramp, while base Gummel number is kept constant in both the devices. The N/sub B/ ramp is controlled such that it minimizes the decelerating field component and a net accelerating field in quasi-neutral base of DrDHBT for minority electrons could be achieved. This increases the drift component of electron current in the quasi-neutral base, which gives rise to an increased current gain and improved cut-off frequency in DrDHBT depending on the value of drift-field parameter. Therefore, an optimized base doping profile could be implemented in place of uniform base doping for further improvement over uniform-N/sub B/ SiGe DHBTs.