DEFECTS INDUCED IN P-TYPE SILICON BY PHOTOCATHODIC CHARGING OF HYDROGEN

Capacitance-voltage (C-V) and current-voltage (I-V) measurements were used to study the effects of photocathodic charging of hydrogen in boron doped (4.5 x 10(16) cm-3) crystalline silicon. The electrolyte was a 5% hydrofluoric solution. Within the first minutes of hydrogenation, a negative charge variation occurs at the surface, due to the formation of a thin hydride-like layer. The hydrogen charging over an extended period of time (congruent-to 30 h) results in a drastic increase in the reverse dark current I(D). This effect can be totally suppressed when the electrodes are stepped to rest-potential (0 bias) for about 20 min. The resulting I-V characteristics are similar to those obtained f or a nonhydrogenated sample. However, the surfaces exhibit a rough aspect, and ellipsometry measurements show that an amorphized layer is present. Secondary ion mass spectrometry measurements reveal that hydrogen (deuterium) is also injected up to 100 nm depth. It is concluded that an amorphous hydrogenated layer forms during an electrolytical charging, due to the incorporation of a high density of hydrogen atoms within the surface region. The raise of I(D) is ascribed to hydrogen-induced defects, operating as electron-hole generation centers. This layer partly dissolves when the cathodic polarization is removed (0 bias condition) and consequently I(D) vanishes.