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Two-dimensional electron gas (2DEG) has been studied extensively because of its abundant physical properties, but no effort has been made to construct p-n or Schottky heterojunctions based on it. Here, we report a universal, practical Ar+-ion-bombardment assistant (AIBA) method to achieve a junction contact between a film of a p-type semiconductor (or metal) and 2DEG. Several materials have been attempted to verify the AIBA method, including a two-dimensional semiconductor (WSe2), an oxide superconductor (YBa2Cu3O7), an amorphous material (amorphous carbon) thin film, and a metal (Au). Despite different growth methods, all of the samples exhibit clear heterointerfaces and good rectifying behaviors, which indicates the formation of p-n and Schottky junctions. Different from the traditional methods to fabricate the vertical heterojunctions by layer-by-layer growth, the AIBA method enables us to achieve lateral heterojunctions, which may lead to remarkable physical properties. These as-fabricated heterostructures show significant photoconductivity at room temperature. This work paves the way for functional 2DEG-based devices with lateral heterojunctions.

Positive magnetoresistance (PMR) and negative magnetoresistance (NMR) describe two opposite responses of resistance induced by a magnetic field. Materials with giant PMR are usually distinct from those with giant NMR due to different physical natures. Here, we report the unusual photomagnetoresistance in the van der Waals heterojunctions of WSe 2 /quasi-two-dimensional electron gas, showing the coexistence of giant PMR and giant NMR. The PMR and NMR reach 1,007.5% at – 9 T and – 93.5% at 2.2 T in a single device, respectively. The magnetoresistance spans over two orders of magnitude on inversion of field direction, implying a giant unidirectional magnetoresistance (UMR). By adjusting the thickness of the WSe 2 layer, we achieve the maxima of PMR and NMR, which are 4,900,000% and – 99.8%, respectively. The unique magnetooptical transport shows the unity of giant UMR, PMR, and NMR, referred to as giant bipolar unidirectional photomagnetoresistance. These features originate from strong out-of-plane spin splitting, magnetic field–enhanced recombination of photocarriers, and the Zeeman effect through our experimental and theoretical investigations. This work offers directions for high-performance light-tunable spintronic devices.NMR)

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