InGaN/GaN, InGaN/InGaN and InGaN/AlInGaN multi-quantum-well (MQW) laser diodes (LDs) were grown on (0001) sapphire substrate by metalorganic chemical vapor deposition (MOCVD). The GaN (0002) synchrotron X-ray diffraction (XRD), electroluminescence (EL) and optical power-current (L-I) measurement reveal that AlInGaN quaternary alloys as barriers in MQWs can improve the crystal quality, optical emission performance, threshold current and slope efficiency of the laser diode structure to a large extent compared with other barriers. The relevant mechanisms are that: 1. The Al component increases the barrier height of the MQWs so that more current carriers will be caught in. 2. The In component counteracts the strain in the MQWs that decreases the dislocations and defects, thereby the nonradiative recombination centers are decreased. 3. The In component decreases the piezoelectric electric field that makes the electrons and the holes recombine more easily.