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.