In0.15Ga0.85N/GaNandIn0.15Ga0.85N/In0.05Ga0.95Nmulti quantum well (MQW) structures grown on (0001) sapphire substrates were investigated by high-resolution x-ray diffraction and cross-sectional transmission electron microscopy. The results show that ultrathin MQWs with fairly good crystallinity and precisely controlled clear parallel interfaces were grown. Laser diode structures with MQWs were also studied, and the results suggest that these superlattice structures retain their high quality even after being subjected to high temperatures during the subsequent growth ofp-type GaN as the optical guiding layer,p-type GaAlN as the cladding layer, andp-type GaN as the contact layer. ©1997 American Institute of Physics.