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\subsubsection{\texorpdfstring{CNT-Si junctions-based optoelectronic devices}{CNTSi junctionsbased optoelectronic devices}}
\label{sec:cntsi_junctionsbased_optoelectronic_devices}


Recent progress in silicon photonics has dramatically advanced the
possible realization of heterogeneous logic circuits. A variety of
Boolean optoelectronic circuits have been proposed5. In this context,
experimental investigation of logic operations with both optical and
electrical inputs in chip-integrable devices is highly desirable.
Here, we present a new kind of photodiode-based logic device using
scalable heterojunctions of carbon nanotubes and silicon, the output
currents of which can be manipulated completely by both optical and
electrical inputs. This provides a novel platform for heterogeneous
optoelectronic logic elements with voltage-switchable photocurrent
responsivity of \textgreater  1 AW\textsuperscript{-1}, photovoltage responsivity 
of \textgreater 1×10\textsuperscript{5} VW\textsuperscript{-1}, electrical on/off ratios 
of \textgreater 1×10\textsuperscript{5} and optical on/off ratios of \textgreater 1×10\textsuperscript{4}. 
To demonstrate their scalability, we fabricated a large array of
photoactive elements on a centimetre-scalewafer. We also present
bidirectional phototransistors and novel clock-triggerable logic
elements such as a mixed optoelectronic AND gate, a 2-bit
optoelectronic ADDER/OR gate and a 4-bit optoelectronic
digital-to-analog converter.

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