lithium-ion batteries, [12,13] and electromagnetic interference shielding. [14,15] In addition to these above-mentioned applications, the excellent performance of MXenes makes them ideal for the research in MXene-semiconductor devices. [16] To be specific, MXenes colloidal solution can be fabricated into high-quality thin film through simple methods, such as drop casting and spin-coating, [17,18] thus simplifying the fabrication process of the devices. Besides, MXenes thin film possesses high transmittance and low sheet resistance, [19] which benefits their applications in photodetectors and LEDs. Moreover, the work function of MXene is adjustable in a large range from 2.14 to 5.65 eV, [20,21] which allows it to form Schottky junctions with different semiconductor materials, thereby broadening its application situations.So far, van der Waals heterostructures formed by other 2D materials (such as graphene and TMDs) and conventional semiconductor materials have been investigated widely in various fields and exhibits excellent characteristics. [22][23][24] However, van der Waals heterostructures fabricated by MXene and semiconductor materials have rarely been investigated so far and still need further study. Moreover, as an ideal candidate for optoelectronic devices, GaN has been widely used in photodetectors and LEDs. [25][26][27][28] In this work, Ti 3 C 2 T X /(n/p)-GaN van der Waals heterostructures were fabricated and studied. Ultraviolet photoelectron spectroscopy (UPS) confirms that Ti 3 C 2 T X can form Schottky contacts with both n-GaN and p-GaN at room temperature. By taking the advantages of the Ti 3 C 2 T X /(n/p)-GaN Schottky junctions, we fabricated high-speed photodetectors and stable orange LEDs, respectively. Under the illumination of a 365 nm light source with an intensity of 96.9 µW cm −2 , the Ti 3 C 2 T X /n-GaN photodetector shows a short rise time (60 ms) and decay time (20 ms), a high responsivity (44.3 mA W −1 ) and on/off ratio (≈11 300). And the Ti 3 C 2 T X /p-GaN LED device remains stable orange light emission under bias voltage from 4 to 22 V. We believe that this work gives an essential strategy for photodetectors and LEDs by taking the advantages of MXenes. Due to their excellent electrical conductivity, high transmittance, and adjustable work function, 2D transition-metal carbides and nitrides have shown great promise in optoelectronic applications, especially in MXenesemiconductor devices. In this work, Ti 3 C 2 T X /(n/p)-GaN van der Waals heterostructures are fabricated and studied. The Ti 3 C 2 T X /(n/p)-GaN Schottky junctions are confirmed by ultraviolet photoelectron spectroscopy (UPS) with a work function ≈4.2 eV of Ti 3 C 2 T X . Based on the Ti 3 C 2 T X /(n/p)-GaN Schottky junctions, high-speed photodetectors and stable orange light emitting diodes (LEDs) are fabricated. The Ti 3 C 2 T X /n-GaN heterostructure photodetector shows a short rise time (60 ms) and decay time (20 ms), a high responsivity (44.3 mA W −1 ) and on/off ratio (≈11300) under a light source of 365 nm wa...

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