Fast-Response Avalanche Photodiode Using Multi p-n Junctions

Photodiodes are widely used across various industries and play a critical role especially in autonomous vehicles, defense and security systems. In these fields, the fast response time in photodiode is directly linked to safety issues, thus, accurate and efficient light detection is required. Conventional silicon photodiodes (Silicon PDs) have limitation in detection, only for visible light, due to their bandgap. To overcome this limited detection range, compound semiconductors like germanium (Ge) and indium gallium arsenide (InGaAs) have been studied. However, compound semiconductors require complex epitaxial growth on different substrates respectively, due to their lattice mismatch, resulting high-fabrication costs. Here, we propose a novel near-infrared (NIR) avalanche photodiode (APD) design using a 2D material, MoTe₂, as the channel material. In comparison with Ge and InGaAs, our device has benefits on time and cost, avoiding the need for complex epitaxial processes while maintaining high performance. Bandgap (0.88 eV)¹ of MoTe₂ covers detection range to NIR^{2, 3}. Moreover, MoTe₂, which has ambipolar characteristic⁴, enables precise p-n junction control by tuning the Fermi level through electrostatic doping. By adopting our previous work: multi-p-n junction structure⁵, our device can increase Avalanche Bullets (ABs) which are photo charge carriers that can induce avalanche multiplication. An increased number of ABs can significantly improve the probability of impact ionization in the MoTe₂ lattice, greatly enhancing current-rising speed to the saturation region when light is applied. The photodiode with our multi p-n junctions structure can be a road map for improving fast response time compared to existing PDs, and is expected to be a solution for safety issues on current and upcoming-autonomous technologies.<br/><br/><br/>Reference:<br/>1. <i>Nano letters</i>, 2015, 15.4: 2336-2342.<br/>2.<i> ACS applied materials & interfaces</i>, 2017, 9.6: 5392-5398.<br/>3. <i>Small</i>, 2017, 13.24: 1700268.<br/>4.<i> Advanced Materials,</i> 2014, 26.20: 3263-3269.<br/>5. <i>Advanced Materials</i>, 2022, 34.7: 2107468.