Three-dimensional Dirac semimetal ${\mathrm{Cd}}_3{\mathrm{As}}_2$ exhibits excellent properties including high carrier mobility and a linear dispersion relation, with promising applications in ultrafast and broadband photodetection and optical communications. Here, we demonstrate that the transient photovoltage in ${\mathrm{Cd}}_3{\mathrm{As}}_2$ nanobelt field-effect transistors can be greatly enhanced in devices with Schottky junctions. In such devices, the photovoltage polarity reverses at high pump fluence, persisting up to room temperature. The photovoltage can be modulated over 300% within a few picoseconds, providing a unique material platform for potential ultrafast optical switching applications. In contrast, the modulation is only up to 30% in devices with Ohmic contacts. We attribute the photovoltage reversal to the competing photothermoelectric and lateral photo-Dember effects, supported by numerical modeling.

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• Photocurrent
• Topological materials
• Dirac semimetal
• Nanostructures
• Finite-element method
• Ultrafast femtosecond pump probe