Noise modeling of an InP/InGaAs heterojunction bipolar phototransistor

Abstract

We present a theoretical analysis of the noise behavior of a heterojunction bipolar transistor (HBT) used as a three terminal (3T) photodetector. The use of a HBT in the photodetector mode can greatly simplify the fabrication of HBT-based optical receivers in the monolithic form. The present model takes into account the effect of the received light on the intrinsic parameters and various noise components of the HBT when used as a detector. The model enables one to determine the signal-to-noise ratio at the output and also the noise equivalent power of the HBT. The model has been applied for characterization of an InP/ InGaAs HBT used as a 3T photodetector in the 1.55-m wavelength region.

Signal-to-noise ratio for a Ge-GeSn-GeSn Hetero PhotoTransistors at 1.55 µm

“…In our work [13] Unfortunately, however, no data for GBW and SNR for InGaAs-based HPT are available for the structure we have considered in this work. Chakrabarti et al [12] presented the values of GBW and SNR for HPTs with InGaAs as the base. Both the works [12,13] rely on the theory developed in [9].…”

“…The noise equivalent circuit considered in this work has been developed by Chakraborti et al [12] and is shown in Fig. 2.…”

“…The necessary modification required to incorporate frequency of an intrinsic transistor is -inclusion of the time derivative term in the continuity equation while solving for the carrier density and terminal currents. In order to do this, the diffusion length for the minority carriers are modified to have frequency dependent term as [12], where, ω is the angular frequency of excitation. This makes all the terminal currents, photo current density and the transport factors frequency dependent.…”

“…the total effective collector-base capacitance defined in detail [12]. The mean square output noise power across the equivalent output resistance eq R is given by,…”

“…A useful alternative, a Heterojunction Photo Transistor (HPT), provides optical gain like APD, but no excess noise to the contrary. Several workers studied the performance of HPTs with GaAs or InGaAs as the base layer [9][10][11][12]. Recently, gain and responsivity of GeSn based HPTs have been reported [13].…”