SEMICONDUCTOR SURFACE SPECTROSCOPIES - THE EARLY YEARS

In the Fall of 1970, Chester Lee Balestra, a graduate student working in Harry Gates' laboratory at the Massachusetts Institute of Technolog y, observed a strong photovoltaic signal on CdS surfaces illuminated w ith a sub-bandgap light. Part of the photovoltage spectrum disappeared for surfaces cleaved in ultra-high vacuum and reappeared at higher am bient pressure, implying the involvement of surface states. A correspo nding technique, ''surface photovoltage spectroscopy'', was developed and used for studying a wide range of surface-related phenomena in sem iconductors. Two decades later, the spin-off techniques are used on si licon IC fabrication lines for instantaneous, non-contact detection of metal contaminants with an astounding sensitivity of one part per qua drillion.