Lasing and ion beam doping of semiconductor nanowires Semiconductor nanowires exhibit extraordinary optical properties like highly localized light emission efficient waveguiding and light amplification. Even the stimulation of laser oscillations can be achieved at optical pumping making nanowires promising for optoelectronic applications. For successful integration into future devices three major key challenges have to be faced: 1) the understanding of the fundamental properties 2) the modification of the emission characteristics and 3) the investigation of the efficiency limiting factors.