Gate-tunable broad-spectrum avalanche photodetector based on WSe₂/MoTe₂ type-I heterojunction

Two-dimensional materials have demonstrated revolutionary potential in optoelectronic devices due to their atomic-scale thickness, high carrier mobility, and broad bandgap coverage. Among them, tungsten diselenide (WSe₂) and molybdenum ditelluride (MoTe₂), as representative members of the transition metal dichalcogenide (TMD) family, can be vertically stacked to form a type-I van der Waals heterojunction, offering a strategy for designing high-performance avalanche phototransistors (APTs). The core operating principle of an APT relies on carrier avalanche multiplication under a high electric field. When the device enters the avalanche breakdown regime, a strong electric field accelerates hot carriers, inducing impact ionization via collisions with the lattice and thereby generating a large number of electron-hole pairs. Unlike conventional type-II heterojunctions, in a type-I configuration, the wide-bandgap component (e.g., WSe₂) functions as a barrier layer that effectively suppresses carrier recombination, while photo-generated carriers in the narrow-bandgap material (e.g., MoTe₂) can cross the interface through tunneling, markedly improving carrier collection efficiency and response speed. This property allows the type-I heterojunction to significantly suppress thermal noise in the APT before reaching the critical voltage. Combined with the inherently low dielectric constant and atomic-scale thickness of 2D materials, avalanche breakdown can be achieved at substantially lower bias voltages, greatly reducing power consumption and the risk of thermal damage.