InGaN/GaN　multiple　quantum　well　(MQW)　structures　were　grown　by　MOCVD.　A　strain-relief　underlying　layer　was　employed　to　reduce　the　strain　in　the　InGaN　well　layers　arising　from　the　large　lattice　mismatch　between　InN　and　GaN.　Samples　were　investigated　by　photoluminescence　(PL),　electroluminescence　(EL)　and　atom　force　microscopy　(AFM)　to　characterize　their　optical　and　morphological　properties.　By　inserting　an　underlying　layer,　the　PL　intensity　was　increased　more　than　three　times.　Under　small　injection　current　(1-15　mA),　the　blue-shift　of　EL　peak　wavelength　was　decreased　from　8　to　1.8　nm,　the　surface　morphology　was　improved　and　the　density　of　V-pits　was　reduced　from　14-16　x　10(8)　to　2-4　x　10(8)/cm(2).　Further,　the　20-mA　output　power　was　increased　by　more　than　50%.　(c)　2007　Published　by　Elsevier　Ltd.