Abstract
Mesoporous silicon and porous silicon/Ni nanocomposites have been investigated in this work employing light-dark surface photovoltage (SPV) transients to monitor the response of surface charge dynamics to illumination changes. The samples were prepared by anodization of a highly n-doped silicon wafer and a subsequent electrodepositing of Ni into the pores. The resulting pores were oriented towards the surface with an average pore diameter of 60 nm and the thickness of the porous layer of approximately 40 μm. SPV was performed on a bare porous silicon as well as on a Ni-filled porous silicon in vacuum and in different gaseous environments (O2, N2, Ar). A significant difference was observed between the ‘light-on’ and ‘light-off’ SPV transients obtained in vacuum and those observed in gaseous ambiences. Such behavior could be explained by the contribution to the charge exchange in gas environments from chemisorbed and physisorbed species at the semiconductor surface.PACS81.05.Rm; 73.20.-r; 75.50.-y; 82.45.Yz
Highlights
Porous silicon (PS) exhibits numerous properties directly related to its microstructure, which in turn can be modified within a broad range of morphologies
It is likely that physisorption, chemisorption, or desorption of gas species govern the observed charge dynamics. Both the internal and external charge transfer mechanisms occur in PS simultaneously but on different time scales resulting in non-trivial transients
The electrons in the trap states at the interface may recombine with the flux of holes from the Si side leading to the initial decrease of the contact potential difference (CPD) in the light-on transient
Summary
Porous silicon (PS) exhibits numerous properties directly related to its microstructure, which in turn can be modified within a broad range of morphologies. Due to the high surface area and the high reactivity, such as-etched PS oxidizes . It can be oxidized, e.g., by storing in air (native oxide layer) and via thermal or chemical treatment. Oxidation is the main aging aspect and knowledge about the oxidation state of the surface is of importance. Light illumination decreases the H-termination of as-etched samples. Photoirradiation in an oxygen ambient causes photo-oxidation at the surface and accelerates aging of the material. Chemical stability of PS is one of the preconditions rendering the material compatible with any application for which surface modification is desirable
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