Electrical Transport of Nb-Doped MoS₂ Homojunction P-N Diode: Investigating NDR and Avalanche Effect

2D transition metal dichalcogenides (TMDCs) are promising candidates for next-generation nanoelectronics and optoelectronics. Yet, controlling layer number, stacking angle, and interfacial quality in van der Waals (vdW) heterostructures remains challenging, often limiting device performance and reproducibility. Homojunctions formed within a single 2D material can circumvent these issues, but their reliable fabrication and systematic exploration of exotic quantum phenomena remain elusive. Here, we report the fabrication and characterization of a thickness-modulated lateral p-n homojunction from a single flake of Nb-doped MoS₂. This configuration suppresses interface traps without external interface engineering, enabling excellent and highly stable device performance. The diodes exhibit strong rectifying behavior with a rectification ratio of ≈10⁴ and a remarkably low ideality factor (η = 1.23). Notably, we observe field-dependent negative differential resistance (NDR) at low temperatures, offering unique prospects for unconventional electronic applications. The devices also achieve high photoresponsivity (1.09 × 10³ A W^-1), external quantum efficiency (2.16 × 10⁵%), and detectivity (7.5 × 10¹⁰ Jones). Furthermore, electrical breakdown studies reveal avalanche multiplication at relatively low voltages, enabling high-performance avalanche photodetectors. Overall, our results demonstrate a simple yet robust approach for probing carrier multiplication in 2D homojunction p-n diodes, underlining the broad potential of TMDCs in advanced optoelectronic and quantum device applications.