pn-Junction light-emitting diodes (LEDs) were realized by implanting boron ions into n-Si wafers. Different diode designs and diode areas were used to exploit edge effects. Provided that surface recombination is of minor importance, the lateral diffusion current in the n-wafer increases the ratio of radiant and nonradiant current contributions. Thus, an improved internal quantum efficiency of 2.5% resulted from selectively boron implanted LEDs with a reduced width of 50 mu m. (c) 2007 The Electrochemical Society.