we have investigated the effects of light illumination in the wavelength range 1 $mu$ m to 2200 angstrom (with and without dc bias) on the hg//0//. //7cd//0//. //3te (n-type)/sio//2-photox interface at 77 k in the metal-insulator-semiconductor device configuration. illumination of wavelength $lambda$ without bias produced a flatband shift ( $trian op$ u//f//b) towards positive values. the saturation value of $trian op$ u//f//b has a pronounced peak at $lambda$ $equals$ 2800 angstrom and is negligible for $lambda$ $greater than equivalent to$ 5100 angstrom. the light-induced charge is maintained for at least 8 h at 77 k but leaks off if the device is heated briefly to 300 k. we propose a model to explain these results involving light-induced charging and discharging of very slow trap states in the sio// 2-photox (at or near the interface) with an energy distribution centered about 4. 5 ev above the oxide valence band. (edited author abstract) 9 refs