Modeling and Analysis of an 80-Gbit/s SiGe HBT Electrooptic Modulator

We present a rigorous electrical and optical analysis of a strained and graded base SiGe Heterojunction Bipolar Transistor (HBT) electrooptic (EO) modulator. In this paper, we propose a 2-D model for a graded base SiGe HBT structure that is capable of operating at a data bit rate of 80 Gbit/s or higher. In this structure, apart from a polysilicon/monosilicon emitter
$(\hbox{Width} = 0.12\ \mu\hbox{m})$
and a strained SiGe graded base
$(\hbox{Depth} = 40\ \hbox{nm})$
, a selectively implanted collector (SIC)
$(\hbox{Depth} = 0.6\ \mu \hbox{m})$
is introduced. Furthermore, the terminal characteristics of this new device modeled using MEDICI are closely compared with the SiGe HBT in the IBM production line, suggesting the possibility of fast deployment of the EO modulator using established commercial processing. At a subcollector depth of 0.4
$\mu\hbox{m}$
and at a base-emitter swing of 0 to 1.1 V, this model predicts a rise time of 5.1 ps and a fall time of 3.6 ps. Optical simulations predict a
$\pi$
phase shift length
$({ \rm L}_{\pi})$
of 240.8
$\mu\hbox{m}$
with an extinction ratio of 7.5 dB at a wavelength of 1.55
$\mu\hbox{m}$
. Additionally, the tradeoff between the switching speed,
$L_{\pi}$
and propagation loss with a thinner subcollector is analyzed and reported.