A sintered nanoparticle p-n junction observed by a Seebeck microscan

Abstract

A nanoparticular p-n junction was realized by a field-assisted sintering process, using p-type and n-type doped silicon nanoparticles. A spatially resolved Seebeck microscan showed a broad transition from the positively doped to the negatively doped range. Overshoots on both sides are characteristic for the transition. Despite the tip size being much larger than the mean particle size, information about the dopant distribution between the particles is deduced from modeling the measured data under different assumptions, including the limited spatial resolution of the tip. The best match between measured and modeled data is achieved by the idea of doping compensation, due to the sintering process. Due to a short time at high temperature during the field-assisted sintering process, solid state diffusion is too slow to be solely responsible for the observed compensation of donors and acceptors over a wide range. Therefore, these measurements support a densification mechanism based on (partial) melting and recrystallization.

Probing thermopower on the microscale

“…Sharp property gradients are typically found in p–n or Schottky junctions, implying strongly localised depletion zones within their space charge regions, yielding a characteristic overshoot of the spatial Seebeck coefficient. Basically similar characteristics of thermopower whereas on a much wider local scale could be observed recently on sintered bulk materials from nanoscopic base powders 52. Microscanning by means of the Potential‐Seebeck Microprobe (PSM 53) mapped an overshooting S at the studied p–n region.…”

Nonthermal Plasma Synthesis of Nanocrystals: Fundamental Principles, Materials, and Applications

“…Becker et al sintered films of microwave plasma-produced p - and n -type Si nanocrystals with doping concentrations of 5 × 10 20 cm –3 and 2 × 10 20 cm –3 , respectively . They used field-assisted sintering which makes use of pressure and of Joule heating to sinter the nanocrystals. , Using a Seebeck microscan technique, the authors observed a spatial spreading of the p- and n- type dopants in the sintered p–n junction. They interpreted this observation as a mixing of p- and n- type nanocrystals during the sintering process .…”

“…They used field-assisted sintering which makes use of pressure and of Joule heating to sinter the nanocrystals. , Using a Seebeck microscan technique, the authors observed a spatial spreading of the p- and n- type dopants in the sintered p–n junction. They interpreted this observation as a mixing of p- and n- type nanocrystals during the sintering process . The consequent compensation of doping within the intermixing region reduced the charge carrier concentration at the interface.…”

Efficient p-n junction-based thermoelectric generator that can operate at extreme temperature conditions

“…A temperature of 1200 °C is reached with a heating rate of 30 K min -1 and then held for 5 min. For more details about the preparation of the nanostructured pn junctions see references [22,23]. The densified p-n junction is cut to a geometry of 4 mm x 3 mm x 11 mm.…”