The noise due to photocurrent at low frequencies (3-100 kHz) has been observed Of planar aluminium/n-type silicon/ aluminum (Al/n-Si/Al) structures based on low-resistivity silicon. It was found that these Structures exposed to illumination showed Much lower noise than the full shot noise above 5 kHz under a certain operating condition. If the Current noise power spectrum is expressed as S(omega) - 2el(p)Gamma(2), where e is the electronic charge and I-p is the photocurrent, the noise ratio Gamma(2) lies between 0.2 and 1.0, depending on the bias voltage. These results are attributed to the planar structures of the samples having wide electrode separation. Spatially uniform carrier generation due to illumination at the active surface and the decrease in the cross-correlation between the Current components in the structure might be playing the key role to reduce the noise to lower levels than that of full shot noise under a certain operating condition. (C) 2003 Elsevier Ltd. All rights reserved.