Boron- And Phosphorus-Doped Silicon And Germanium Nanocrystals: Preparation And Application

Semiconductor nanocrystals (NCs) have shown great potential in the applications of various fields such as electronics, optoelectronics, photovoltaics, bioimaging, and energy. Given the fact that the success of all kinds of bulk semiconductors largely depends on their doping, doping for semiconductor NCs has been regarded as being critical to the development of semiconductor-NC-based structures and devices. Despite the challenge in the doping of semiconductor NCs progress has been recently made on the doping of compound semiconductor NCs such as CdSe and PbSe NCs. The study of Si NCs and Ge NCs in doping has been largely lagged behind. The main reason is that solution method is difficult to synthesize doped Si NCs or Ge NCs due to the relatively high crystallization temperature of Si and Ge.In this paper, we successfully synthesized P-and B-doped Si NCs and Ge NCs. Si paste has been prepared by using B-and P-doped Si NCs. Thin film transistors (TFT) based on P-and B-doped Ge NCs have been fabricated by solution process. The main contents of this paper include:1. P-doped Si NCs have been synthesized by a plasma approach. Si paste has been prepared by using P-doped Si NCs. Through a series of comparative experiments, we optimized the Si NCs content, heat-treatment temperature, heat-treatment time and organic solvent. Si paste can remain stable for several months. The doping uniformity of Si paste containing P-doped Si NCs is better than paste containing P2O5.2. B-doped Si NCs have been synthesized by a plasma approach. Chemical analysis results indicate that the B concentration of Si NCs can be tuned by changing the gas flow rate. Si paste has been prepared by using B-doped Si NCs. The doping of Si wafers is performed by screen-printing Si paste at the wafer surface. The doping level can be adjusted by using Si paste with different B concentrations. The Si paste enabled doping leads to varying sheet resistances, which are suitable for device fabrication.3. Ge NCs doped with P at different doping levels are synthesized by nonthermal plasma. The doping efficiency is high at low doping levels. It is found that P preferentially occupies the near-surface region of Ge NCs. Part of P atoms may form clusters, leading to compressive strain for P doped Ge NCs. P doping retards the oxidation of Ge NCs, which is due to the modified surface state and compressive strain induced by P. Although the electrical activation efficiency of P in a Ge NC film is low, the P doping of Ge NCs increases the concentration of electrons in the Ge NC film, improving the film conductivity. It is reasonable to assume that defects such as dangling bonds at the NC surface are passivated by some P atoms, leading to the increase of the electron mobility of a Ge NC film after the doping of P. It is found that the treatment of Ge NC films with the ALD of Al2O3 effectively improves the charge transport in the Ge NC films. This demonstrates a new way to optimize and control the effects of doping in Ge NCs by minimizing the influence of defects in Ge NC films with ALD.6. Ge NCs doped with B at different doping levels are synthesized by nonthermal plasma. TFTs based on B-doped Ge NCs have been fabricated by solution process. The film formed with B-doped Ge NCs is n-type semiconductor owing to slight oxidation and unintentional doping. The B doping of Ge NCs increases the concentration and mobility of electrons in the Ge-NC film. This is because the NC surfaces are passivated by some B atoms. The concentration and mobility of electrons decrease while the B concentration increase due to the p-type doping of B.