The Preparation of IV–VI Semiconductor Nanomaterials

Abstract

Bulk lead chalcogenides are narrow-bandgap semiconductors with facecentred cubic structures, lending themselves to several potential applications, notably in thermoelectrics due to the large gure of merit (ZT) associated with the materials, and photovoltaics due to the ideal position of the quantum-conned bandgap. 1 Bulk PbSe exhibits a bandgap of 0.26 eV and an excitonic diameter of 92 nm. 2 PbTe has a bandgap of 0.25 eV and will reportedly exhibit quantum connement effects below 152 nm diameter 3 (which is the longitudinal Bohr radius; the transverse Bohr radius is reportedly 12.9 nm), whereas PbS has a bandgap of 0.37 eV and an excitonic diameter of 40 nm. 4 Upon quantum connement, the blue shi of the bandgap results in materials with optical properties in the infrared region, making these particles the materials of choice for most infrared-dependent applications, 5 with numerous reports of PbE (E ¼ S, Se, Te)-based photodetectors, 6-9 solar cells, 10-12 LEDS, 13,14 lasers, 15 and eld-effect transistors. 16 Quantum dots (QDs) of lead chalcogenides have even been used as biological labels, 17 where phase transfer of PbS particles using simple thiolated ligands was successful and maintained emission quantum yields of up to 26%. 18 PbSe particles have also been capped with SiO 2 and used in cellular imaging without any obvious toxicity issues. 19,20 Unlike the CdSe family of nanoparticles, which have analogous organic compounds with similar optical properties, there are currently no organic equivalents for strongly luminescent QD infrared emitters such as PbSe.The most common method of preparing QDs is the hot injection method where, for example, a metal salt is dissolved in solution with a capping agent