High responsivity, low dark current, heterogeneously integrated thin film Si photodetectors on rigid and flexible substrates

Sulochana Dhar,David M Miller,Nan M Jokerst

doi:10.1364/oe.22.005052

Abstract

We report thin film single crystal silicon photodetectors (PDs), composed of 13- 25 μm thick silicon, heterogeneously bonded to transparent Pyrex® and flexible Kapton® substrates. The measured responsivity and dark current density of the PDs on pyrex is 0.19 A/W - 0.34 A/W (λ = 470 nm - 600 nm) and 0.63 nA/cm(2), respectively, at ~0V bias. The measured responsivity and dark current density of the flexible PDs is 0.16 A/W - 0.26 A/W (λ = 470 nm - 600 nm) and 0.42 nA/cm(2), respectively, at a ~0V bias. The resulting responsivity-to-dark current density ratios for the reported rigid and flexible PDs are 0.3-0.54 cm(2)/nW and 0.38-0.62 cm(2)/nW, respectively. These are the highest reported responsivity-to-dark current density ratios for heterogeneously bonded thin film single crystal Si PDs, to the best of our knowledge. These PDs are customized for applications in biomedical imaging and integrated biochemical sensing.

Highlights

The heterogeneous integration of thin film photonic devices onto host substrates, and in particular, flexible substrates, enables the development of new integrated structures, including bendable and conformal electronic and photonic systems
Towards the development of an integrated, portable sensing and imaging probe, our group reported preliminary results on highresponsivity, low dark current, heterogeneously bonded, annular, thin-film Si photodetectors developed for low light level biochemical sensing and biomedical imaging systems where portable light sources, low power consumption and high SNR requirements drive the development of high responsivity, low dark current photodetectors [13]
This paper focuses on the development of high responsivity, low dark-current, large-area, single-crystal, rigid and flexible thin film silicon photodetectors for high performance, low operating voltage detection schemes for conformal tissue imaging

Summary

Introduction

The heterogeneous integration of thin film photonic devices onto host substrates, and in particular, flexible substrates, enables the development of new integrated structures, including bendable and conformal electronic and photonic systems. It should be noted that no AR coating or passivation layer was deposited on these PDs. The development of larger arrays composed of the PD elements reported is possible given the scalability of the wafer bonding and DRIE processes for formation and transfer of thin film Si. Patterned thin film Si waveguide arrays, 4 cm in area, have been previously developed using large area wafer bonding and DRIE processing for thin film transfer and substrate removal [15]. Contact annealing temperatures affect contact resistance and dark currents, and processes which enable contact annealing (not necessarily after bonding to the host substrate) are an important consideration for high performance devices

Device characterization and analysis

Bending fatigue characterization of flexible annular thin-film Si PDs

Conclusion and discussion of results