Surface-Interaction-Driven Polarity Switching in II-V Cd₃P₂ Colloidal Quantum Dots for Infrared Photodiodes

Area of Science:

• Materials Science
• Nanotechnology
• Semiconductor Physics

Background:

• Colloidal quantum dots (CQDs) from II-V semiconductors are promising for infrared optoelectronics due to their optical and carrier transport properties.
• Understanding and controlling the electronic behavior, specifically carrier polarity, of Cadmium Phosphide (Cd3P2) CQDs has been a significant challenge.

Purpose of the Study:

• To establish polarity control in Cd3P2 CQD solids for the development of infrared photodiodes.
• To investigate the influence of synthesis parameters and surface chemistry on the electronic properties of Cd3P2 CQDs.
• To demonstrate a functional homojunction photodiode utilizing Cd3P2 CQDs.

Main Methods:

• Precise control of oleic acid concentration during CQD synthesis to achieve monodispersity and suppress fusion.
• Electrical characterization of Cd3P2 CQD films to study carrier transport and polarity.
• Spectroscopic analysis and first-principles calculations to understand the mechanism of oxygen-induced polarity transition.
• Fabrication and testing of Cd3P2-based homojunction CQD photodiodes.

Main Results:

• Monodisperse Cd3P2 CQDs with suppressed nanocrystal fusion and photoluminescence quantum yields up to 62% were synthesized.
• An oxygen-induced transition from n-type to p-type transport was observed in Cd3P2 CQD films, attributed to surface acceptor states.
• A Cd3P2-based homojunction photodiode was successfully fabricated, functioning as both infrared absorber and charge-selective layer.
• The photodiodes demonstrated stable ambient operation with a short-circuit current density of 18 mA cm⁻², external quantum efficiency of 24%, and a fast temporal response of 23 ns.

Conclusions:

• Surface-driven polarity control is a viable strategy for designing II-V CQD optoelectronics.
• Cd3P2 CQDs represent a promising material platform for developing efficient, low-power infrared conversion technologies.
• The ability to tune carrier polarity in Cd3P2 CQDs opens new avenues for advanced infrared device applications.