THE ELECTROCHEMICAL OXIDATION OF SILICON AND FORMATION OF POROUS SILICON IN ACETONITRILE

The photoelectrochemical oxidation and dissolution of silicon has been investigated in the absence of water and oxygen. The etch rate and ph otocurrent for n-Si in an anhydrous, HF-acetonitrile solution were dir ectly proportional to light intensity. Four electrons were transferred per silicon oxidized, with a quantum yield greater than 3.3 due to el ectron injection. The anodic dissolution of p-Si, as Si(IV) without H- 2 gas at up to 1.4 A/cm2, yielded a novel porous structure which exhib ited electroluminescence and photoluminescence. Noninterconnected pore s were formed perpendicular to the surface, and were 1 to 2 mum in dia meter, spaced 2 to 3 mum apart, and over 225 mum long. The profusion o f micropores and quantum size structures (<100 nm), normally found wit h porous silicon produced in aqueous electrolytes, were not detected b y transmission electron microscopy and scanning electron microscopy an alyses. A mechanism for the oxidative dissolution of silicon is propos ed. The luminescence was a function of the pore length and appears to be related to the presence of a dihydride surface. The absence of wate r and oxygen shows that siloxene is not involved in the luminescence. The inability to detect obvious quantum structures, and the insensitiv ity of the luminescence to porous shapes tends to support the a-SiH(x) alloy or surface passivation mechanism of luminescence.