Student/NIMS Graduate Research Assistant
Semiconductor Functional Device group

An anti-ambipolar transistor (AAT) is a heterojunction transistor composed of p- and n-type semiconductors that exhibits negative differential transconductance (NDT). This unique transport characteristic enables the realization of advanced logic circuits, including multivalued and reconfigurable logic circuits. In this study, we prepared an AAT based on two-dimensional (2D) materials, where MoS₂ and WSe₂ thin films grown on sapphire substrates by chemical vapor deposition (CVD) were utilized as the n- and p-type transistor channels, respectively. Importantly, these films were precisely patterned using a Nd: YAG laser. Although mechanical exfoliation techniques are widely used to form 2D-material-based transistors, variations in flake size and thickness limit device-to-device reproducibility and large-scale integration.
　Figure 1(a) shows a schematic illustration and an optical microscope image of the prepared AAT. In this device, Au electrode and HfO₂ layer behave as the bottom gate and gate insulating layer, respectively. A hexagonal boron nitride (h-BN) film was dry-transferred onto the HfO₂ layer to passivate interfacial defects. The CVD-grown MoS₂ and WSe₂ films were then sequentially transferred onto the h-BN/HfO₂ layer to form a MoS₂/WSe₂ heterointerface. The channel region centered around the heterointerface was patterned into a 5 × 15 μm size using Nd:YAG laser with a wavelength of 532 nm. In/Au and MoO₃/Au were used as source/drain electrodes for the MoS₂ and WSe₂ channels, respectively.
　Figure 1(b) indicates the drain current (I_D)–gate voltage (V_G) curve of the prepared AAT measured under vacuum. At a fixed drain voltage (V_D) of V_D = 5.0 V, the gate voltage V_G was swept from −5 to 5 V. I_D started increasing at V_G (V_ON) = −0.8 V and reached a peak I_D (I_Peak) of 1.5 nA at V_G (V_peak) = 0.6V. Subsequently, I_D decreased with increasing V_G and was completely suppressed at V_G (V_OFF) = 1.7 V and reached a Valley I_D (I_Valley) of 29.6 pA. The PVR, which is the ratio of IPeak to I_Valley, was calculated as 52. These results exhibit typical NDT behavior. As described above, the proposed formation method provides a promising platform for reproducible 2D-material-based AATs and their integration into functional circuits, including applications in multivalued logic circuits in future.