Vedatrayee Chakraborty

Effect of different loss mechanisms in SiGeSn based mid-infrared laser

We have analyzed the mid-infrared SiGeSn based Barrier-Well-Barrier Heterostracture and calculated the transparency carrier density and corresponding current density for the structure. The effects of different loss mechanisms like free carrier absorption, spontaneous recombination and Auger recombination processes on the transparency current density have been examined. It is shown that, the transparency current density increases significantly with the injected carrier density. Different scattering processes like acoustic phonon scattering and intervalley optical phonon scattering are taken into consideration for this analysis of free carrier absorption mechanisms.

Modeling of tunneling current density of GeC based double barrier multiple quantum well resonant tunneling diode

The double barrier quantum well (DBQW) resonant tunneling diode (RTD) structure made of SiGeSn/GeC/SiGeSn alloys grown on Ge substrate is analyzed. The tensile strained Ge1−zCz on Si1−x−yGexSny heterostructure provides a direct band gap type I configuration. The transmission coefficient and tunneling current density have been calculated considering single and multiple quantum wells. A comparative study of tunnelling current of the proposed structure is done with the existing RTD structure based on GeSn/SiGeSn DBH. A higher value of the current density for the proposed structure has been obtained.

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

Heterojunction Photo Transistors (HPTs) provide optical gain but no excess noise. Recently good quality alloys of GeSn are regularly grown on Si substrate, opening up the possibility of having lasers, photodetectors etc. using standard VLSI technology. In this paper signal-to-noise ratio (SNR) for an HPT having GeSn as base has been estimated at telecommunication wavelength of 1.55 µm. The calculated gain-bandwidth product indicates high values and satisfactory SNR.

Predicted performance of Ge/GeSn hetero-phototransistors on Si substrate at 1.55 µm

Alloys of Ge and Sn grown on Si platform show about tenfold increase in absorption over Ge at L-band due to direct nature of the band gap. We have made use of it by designing a Ge/GeSn/GeSn heterophototransistor on Si. A thermionic-field-diffusion model is employed to calculate the current, optical gain and responsivity. The values are comparable with those for InP/InGaAs/InGaAs Npn devices.

Free carrier absorption in Sn based Group-IV alloys

The free carrier absorptions in strained Ge, relaxed GeSn and strained GeSn are estimated considering different scattering mechanisms, namely, acoustic phonon, non polar optical phonon and intervalley phonon scatterings. The change in absorption coefficient for different Sn concentration in the alloys is also reported.

GeSn/SiGeSn RCE photodetectors: A comparative study based on Franz-Keldysh effect and quantum confined stark effect

Ge-based photodetectors are currently studied for providing cheap solution to long haul and short distance communication and optical interconnects. Tensile strained Ge layers grown with suitable barriers show direct gap type I band alignment. We have worked on resonant cavity enhanced (RCE) photodetectors using GeSn/SiGeSn type I structure. Performance of photodetectors using strong Quntum Confined Stark Effect, and Franz-Keldysh Effect in these structures and properties related to photodetection are studied in this paper.