The impact of scaling on off-state current of p-i-n diodes is studied. A sub-micron p-i-n diode exhibits a dominating surface component of leakage current. Variation in i-layer thickness has an impact on bulk leakage. Bulk leakage scales with cross-sectional area of the diode and surface leakage has been controlled using surface treatments to give ultra low leakage currents of 210 fA for a device of cross sectional area of 0.44 mu m(2). Devices of 100 nm i-layer thickness show an average bulk and surface current densities of 100 mA/cm(2) and 150 fA/mu m, respectively. (C) 2015 Elsevier Ltd. All rights reserved.