The formation of porous silicon by irradiation with low-energy ions

Abstract

The paper presents experimental data on the formation of porous layers in silicon by high-dose (>1015 ions/cm2) implantation of low-energy ions (≤30 keV). The pore diameter in the plane of the parallel surface is almost two orders of magnitude larger than their size in the plane perpendicular to the surface. Pores are formed as a result of the formation of local melts in the surface layer from “overheated” thermal spikes. Pores are formed in the process of solidification of the melts due to the difference in the volume of solid and liquid phases. The combination of “nano-pores” in the process of subsequent ion irradiation and (or) post implantation annealing leads to the formation of “micro-pores”. During ion sputtering, pores can “come out” to the surface, creating a surface relief such as pits. In the case of very dense targets and heavy (or cluster) ions, conditions arise for the formation of a sponge-like surface. Porous Si layers are characterized by luminescence with a spectrum close to white light. The position of the spectrum maximum depends on the irradiation and annealing regimes. Silicon nanocrystals forming the pore surface, as well as a thin oxide film on the surface of nanocrystals, are responsible for the observed luminescence.