Precursor Coordination Engineering Enables Epitaxial-Level Carrier Densities in HgTe Colloidal Quantum Dots

Area of Science:

• Materials Science
• Nanotechnology
• Semiconductor Physics

Background:

• Surface traps limit colloidal quantum dots (CQDs) electronic purity, hindering applications in the mid-wave infrared (MWIR) spectrum.
• Achieving low dark noise in MWIR devices requires highly pure semiconductor materials, a challenge for solution-processed CQDs.

Purpose of the Study:

• To investigate the influence of metal halide precursor coordination geometry on CQD passivation efficacy.
• To suppress background carrier densities in CQDs to approach intrinsic levels for improved optoelectronic performance.

Main Methods:

• Utilized mercury(II) bromide (HgBr2) with octahedral coordination and mercury(II) chloride (HgCl2) with linear coordination.
• Employed 1H Nuclear Magnetic Resonance (NMR) spectroscopy and powder X-ray diffraction (pXRD) for mechanistic investigation.
• Verified passivation effectiveness using field-effect transistor (FET), capacitance-voltage (C-V), and Hall measurements.

Main Results:

• Octahedral HgBr2 formed a stable HgBr2(Olam)4 complex, leading to high surface halide coverage (~9 at.%) on HgTe CQDs.
• Linear HgCl2 resulted in weaker coordination and halide-deficient surfaces (<1 at.%) on HgTe CQDs.
• HgBr2-passivated CQDs exhibited suppressed non-radiative recombination and reduced background doping to ~10^14 cm^-3.

Conclusions:

• Coordination geometry of metal halide precursors is a critical factor in achieving electronic purity in CQDs.
• Octahedral coordination enables robust surface passivation, significantly reducing carrier doping for advanced optoelectronics.
• This strategy offers a pathway to high-performance, solution-processed MWIR devices with low dark noise.