Metal-Semiconductor-Metal Photodetector with Interdigitated Graphene Finger Electrodes Fabricated on Ge Epilayer Grown on Si Substrate

Abstract

Based on Ge epitaxial layer grown on Si substrate, we have fabricated metal-semiconductor-metal (MSM) photodetectors (PD) with interdigitated graphene finger electrodes and demonstrated its opto-electrical properties. High quality Ge epitaxial layers were grown on n-type Si (100) wafers with a resistivity of 5 - 15 Ω•cm by using a rapid thermal chemical vapor deposition (RTCVD) method. The monolayer graphene grown on Cu foils using CVD method was transferred onto the cleaned Ge epilayer and was patterned by O2 plasma reactive-ion etching (RIE) process to form interdigitated finger electrodes. From temperature dependent current-voltage (I-V) characteristics, the barrier height of graphene/Ge epilayer Schottky junction was measured to be 0.42 eV, of which value was comparable to the barrier height of graphene Schottky contact to bulk-Ge. The manufactured MSM PD with interdigitated graphene finger electrodes exhibited a considerable spectral response for wavelengths in the range of 1530 – 1560 nm, demonstrating effective photo-detection for the entire C-band (conventional band) spectrum range. On the other hand, for wavelengths > 1560 nm, its responsivity fell off rapidly, which was consistent with the Ge absorption coefficient trend. Under the illumination of incident light with a power of 3.5 mW, the maximum values of responsivity and detectivity at - 2V reverse bias were measured to be 0.35 A/W and 3.86×1010 Jones (cmHz1/2/W) at the wavelength of 1545 nm, respectively.