Process Integration of Few-Layer MoS2 into a-Si:H Heterojunction pin-Photodiodes for extended Infrared Detection
Photodetectors play a significant role in optical communication or sensor applications. One emerging application area are panchromatic or wavelength-selective detection (voltage-dependent sensitivity) systems with an extended wavelength detection range.
Starting point of this work for such extended detectable wavelength range are well-established vertical pin-photodiodes with optical response in the visible spectral range (VIS) based on the mature amorphous silicon (a-Si) thin-film technology platform. Such diodes can easily be integrated on an arbitrary substrate technology and are therefore prone for tandem vertical stack integration. To enhance their detection range, we succeeded in the reproducible and scalable integration of large-area few-layer molybdenum disulfide (MoS2), a 2D transition metal dichalcogenide (TMDC) with tailored optical properties in the IR regime. The 2D semiconductor was successfully integrated on a centimeter-scale utilizing conventional thin-film deposition processes. Despite of MoS2 having a bandgap of 1.4 eV, the resulting hybrid vertically integrated a-Si/MoS2 detector arrays yield a broad absorption range from 400 nm up to at least 2120 nm, probably due to indirect optical transitions at the material interface. Moreover, their photoresponse can be tuned from the VIS to the IR range depending on the applied bias voltage, indicating a very interesting potential for wavelength detection devices. Furthermore, the a Si effectively passivates the MoS2 and ensures a long-term device stability.