Solution-Processed Germanium Nanocrystal Thin Films as Materials for Low-Cost Optical and Electronic Devices

Solution-processed nanocrystal films have attracted significant interest as potential semiconductor materials with size-tunable optical and electronic properties that can be deposited with low-cost printing and coating techniques. Significant progress has been reported with groups II-VI and IV-VI nanocrystal films because the electrically insulating ligands that solubilize the nanocrystals can be easily exchanged or removed after film deposition. Although progress to date has been slow for group IV silicon and germanium nanocrystal films, this paper reports solution-processed germanium nanocrystal films with promising electrical conductivities. Stable germanium nanocrystal colloids are produced via nonthermal plasma synthesis and subsequent alkene surface functionalization. Electrical characterization of drop-cast germanium nanocrystal films reveals that the films are insulating as deposited but have conductivities as large as 10(-6) and 5 x 10(-4) S/cm after annealing at 250 and 500 degrees C, respectively. Mass spectrometry, thermogravimetric analysis, and infrared spectroscopy indicate that the increase in conductivity coincides with the decomposition and departure of the alkyl ligands from the films.