SIZE QUANTIZATION IN SEMICONDUCTOR PARTICULATE FILMS

Slow infusion of H2S onto cadmium arachidate, zinc arachidate, or metal-ion-coated monolayers resulted in the formation of metal sulfide particles which, when transferred to solid substrates in different stages of their growth, produced semiconductor particulate films. CdS and ZnS semiconductor particulate films were established to be predominantly hexagonal and cubic crystallites by X-ray diffraction. Transmission electron and scanning tunneling microscopies, as well as absorption spectroscopy, provided evidence for the initial formation of 30 +/- 5 angstrom, three-dimensional, size-quantized particles. Longer exposure to H2S resulted in the formation of 30-40-angstrom-thick, 30-80-angstrom-diameter CdS polyparticles which ultimately evolved into porous semiconductor films of different thicknesses. The optical-thickness-dependent, direct bandgap shifts and the recovery of bulk bandgaps upon heating the 150-300-angstrom-thick CdS and ZnS semiconductor particulate films were rationalized in terms of size quantization.