posted on 2021-04-01, 23:52authored byShu An, Shaoteng Wu, Kwang-Hong Lee, Chuan Seng Tan, Yeh-Chen Tai, Guo-En Chang, Munho Kim
We have demonstrated high-performance
flexible germanium (Ge) vertical
p–i–n photodetectors (PDs) based on a resonant cavity
structure by a direct flip transfer of Ge nanomembranes on polyethylene
terephthalate (PET) substrates. Finite-difference time-domain simulation
proves that the vertical cavity structure composed of the bottom gold
and top SU-8 layers as a reflector and an anti-reflection surface,
respectively, could enhance the average absorption in the near-infrared
(NIR) region (i.e., 1520–1640 nm) from 0.06
to 0.20 by 233%. Strains introduced into Ge NMs by convex and concave
fixtures are measured to be 0.37 and −0.32%, respectively.
The fabricated PDs exhibit a low dark current density of 9.6 mA/cm2 at −1 V and a high forward–reverse current
ratio of 105 under the flat condition. Responsivity at
1550 nm increases from 52.5 to 133.8 mA/W by tensile strain, while
it slightly decreases to 32.6 mA/W under comparable compressive strain.
Furthermore, the devices show no degradation in their optoelectronic
responses after 200 bending cycles at convex fixtures with a radius
of 30 mm. Overall, such flexible Ge PDs with the capabilities of both
excellent optoelectronic performance and mechanical durability represent
significant advances in the field of group IV NIR optoelectronic devices.