Changes in Minority Carrier Lifetime of Hydrogen-Terminated Si Surfaces in Dry- and Wet-Air

Abstract

Minority carrier lifetime of HF-treated Si(100) surfaces decreases in wet-air more rapidly than in dry-air. XPS measurements show that OH and O are mainly included in Si by keeping in wet-air and dry-air, respectively. OH cannot form network, and thus backbonded OH generates Si dangling bonds. On the other hand, backbonded O can form Si-O-Si networks, leading to the higher lifetime due to lower defect density. When the atmosphere is switched from dry-air to wet-air, the lifetime greatly decreases, and the workfunction increases. These changes are attributed to dominant formation of backbonded OH.Study on initial oxidation of Si is of importance not only from an academic viewpoint but also for application to semiconductor products such as solar cells and LSI. Semiconductor devices are usually fabricated using Si wafers after cleaning with the RCA method 1 followed by hydrofluoric acid (HF) etching. HF-etching forms ideal hydrogenterminated Si surfaces (i.e., only mono-hydride, Si-H) in the case of Si(111), 2 while mono-, di-(Si-H 2 ), and tri-(Si-H 3 ) hydride species are produced on technologically more important Si(100) surfaces. 3-5 HF-etched Si(100) surfaces with Si-H 2 and Si-H 3 are less stable in air than Si(111). Oxidation of HF-treated Si surfaces is enhanced by the presence of metal contaminants, more active species, defects, fluorineadsorbed sites, etc. 6,7 Initial oxidation of HF-treated Si surfaces were investigated using Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), Ultraviolet photoelectron spectroscopy (UPS), etc. 6-9 Chabal et al., 6 reported that when HFtreated Si(100) surfaces were kept in air, vibrational peaks due to SiH, SiH 2 , SiH(O) 3 , and SiH 2 (O) 2 were observed, indicating that O atoms occupied back-bonds with Si-H bonds remaining on Si surfaces. Hirose et al., 7 also concluded that oxygen attacked Si back-bonds and surface Si-H bonds were still present after the oxygen attack.The minority carrier lifetime strongly affects the electrical characteristics of semiconductor devices. 10 It is greatly decreased by the presence of defect states such as interface states. 11,12 In the case of solar cells, photovoltages are markedly influenced by the minority carrier lifetime. 13 Recombination of electron-hole pairs generated in the surface region proceeds at surface states, resulting in a decrease in the quantum efficiency of short-wavelength light, and thus in a decrease in the photocurrent density. 14 Recombination currents possess a large ideality factor, e.g., 2, 15 and thus, a fill factor is also decreased.In the present study, changes of minority carrier lifetime for HFtreated Si surfaces with time kept in air have been investigated. It is found that the minority carrier lifetime strongly depends on humidity, and concluded that hydroxyl species (OH) under the surfaces decreases the lifetime because the species does not form network, resulting in the production of defect states such as Si dangling bonds. ExperimentalPhosphorus-doped n-type Si(100...

Sn species modified mesoporous zeolite TS-1 with oxygen vacancy for enzyme-free electrochemical H2O2 detecting

“…3b), corresponding to the Ti 4+ oxidation state. 31 The O 1s XPS spectra can be fitted to two peaks assigned to Si–O–Si and Ti–O–Si 32 (Fig. 3c).…”