GaInN and GaN were grown by molecular beam epitaxy on c-plane sapphire using NH3. 9 K photoluminescence performed on both GaInN thin layers and GaInN/GaN multiple-quantum wells (MQWs) exhibits narrow emission (similar to 50 meV linewidths). Transmission electron microscopy images show sharp GaInN/GaN interfaces and homogeneous GaInN layers. Strong indium surface segregation is also evidenced. Light-emitting diodes were fabricated from 5 x GaInN (25 Angstrom)/GaN (35 Angstrom) MQW heterostructures. The 300 K electroluminescence yields blue light at 440 nm. (c) 1999 American Institute of Physics. [S0003-6951(99)04124-8].