Optical studies of the structure of porous silicon films formed in p-type degenerate and non-degenerate silicon

Abstract

The detailed structure of porous Si (PS) layers formed in p-type wafers with resistivities 0.01-25 Omega cm has been investigated using reflectance, transmission, ellipsometry and photoluminescence techniques. Marked differences were observed in the optical properties of PS formed in degenerate or non-degenerate Si and these results are correlated with the results of other techniques. The optical techniques together with effective medium modelling have been shown to be useful non-destructive methods for either assessment of PS density or detection of unsuspected phases. The degenerate PS layers consistently showed good retention of the single-crystal characteristics of the starting wafer, only c-Si and voids being detected. For these samples, good agreement was obtained between optical and gravimetric densities. However, the non-degenerate PS had much greater variability, with greater loss of crystallinity and significant incorporation of oxygen, due to partial oxidation having occurred on or immediately after anodisation. Oxide fractions have been determined both optically and gravimetrically, with up to 50% oxide being detected in some samples. Non-degenerate PS samples with high oxygen concentrations appeared to be in the form of a chemical mixture, SiOx, from interpretation of the optical constants. Photoluminescence measurements together with the other techniques indicated a complex mixture of phases in the latter samples-voids, alpha -Si:O (and/or alpha -Si:H), an unknown amorphous phase and silicon oxide. This complex structure probably contributes to the observed instability of thick non-degenerate PS layers when heated in UHV as part of the cleaning procedure prior to epitaxial growth, all degenerate samples being able to withstand heat treatment.

Nanocrystalline Porous Silicon

“…The silicon on sapphire technology (SOS), and silicidation of porous silicon were reported by Ito et al in 1989(Ito et al, 1989. In 1984 Pickering et al (Pickering et al, 1984) have observed the low temperature photoluminescence in PS. But the discovery of room-temperature photo-and electroluminescence by L. Canham in 1990 boosted the research on porous silicon because of the huge potential in silicon-based integrated sensing and photonic devices (Canham, 1990(Canham, , 1997b(Canham, , 1997c(Canham, ,1997dCanham et al,1991).…”

Vapor-phase silanization of oxidized porous silicon for stabilizing composition and photoluminescence

“…2,3 In the 1980's, several studies of the optical properties of PSi were published and photoluminescence ͑PL͒ in the deep red/near infrared was detected at cryogenic temperatures. 4 The roomtemperature luminescence, which has been observed from PSi usually formed in a concentrated HF based electrolyte by Canham 5 in 1990, has attracted considerable attention because of its potential use in the development of silicon-based optoelectronic devices, 6 such as electroluminescent displays 7 and photodetector. 8 The porous structure and a relatively large surface area have also made the silicon an ideal matrix for immobilization of a variety of biomolecules including enzymes, 9 DNA fragments, 10 and antibodies.…”

Dielectric suppression of nanosolid silicon

“…Conventionally, the dielectric response of a porous Si (p-Si) is described by the effective medium approximations [9,10], that simply average the dielectric contribution from the air pores and the backbones of the silicon (nano-Si). The dielectrics of a nano-Si is often presumed to take the bulk constant and the ε nano-Si can be derived from the measured ε eff of a p-Si by using the simple Looygenga formula [11]: …”