1. Department of Chemistry and Chemical Biology,
2. Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 , USA
3. These authors contributed equally to this work

Correspondence to: Charles M. Lieber^1,3 Correspondence and requests for materials should be addressed to C.M.L. (e-mail: Email: cml@cmliris.harvard.edu).

Nanowires and nanotubes carry charge and excitons efficiently, and are therefore potentially ideal building blocks for nanoscale electronics and optoelectronics^{1, 2}. Carbon nanotubes have already been exploited in devices such as field-effect^{3, 4} and single-electron^{5, 6} transistors, but the practical utility of nanotube components for building electronic circuits is limited, as it is not yet possible to selectively grow semiconducting or metallic nanotubes^{7, 8}. Here we report the assembly of functional nanoscale devices from indium phosphide nanowires, the electrical properties of which are controlled by selective doping. Gate-voltage-dependent transport measurements demonstrate that the nanowires can be predictably synthesized as either n- or p-type. These doped nanowires function as nanoscale field-effect transistors, and can be assembled into crossed-wire p–n junctions that exhibit rectifying behaviour. Significantly, the p–n junctions emit light strongly and are perhaps the smallest light-emitting diodes that have yet been made. Finally, we show that electric-field-directed assembly can be used to create highly integrated device arrays from nanowire building blocks.