A Au/ZnS/Fe-quantum dots (QDs)/ZnS/n(+)-GaAs(1 0 0) Schottky-barrier structure containing five layers of spherical Fe QDs with diameter around 3 nm was fabricated by the molecular beam epitaxy technique. its current-voltage (I-V) characteristics measured from 5 to 295 K display negative differential resistance (NDR) for temperature <= 50 K, which is caused by the presence of Fe QDs. The highest peak-to-valley current ratio obtained at 5 K is as high as 15:1. Staircase-like I-V characteristic was also observed at low temperature in some devices fabricated from this structure. Possible mechanisms that can account for the observed unusual I-V characteristics in this structure were discussed. (c) 2008 Elsevier B.V. All rights reserved.