This study examined the origin of visible luminescence from ZnO layers deposited on $p\text{-Si}$ substrates by various growth methods using temperature dependent photoluminescence measurements. The deep level emissions of ZnO layers are found to be strongly dependent on the growth conditions and growth methods used. For the samples grown by sputtering, the visible emission consisted of violet, green, and orange-red regions, which corresponded to zinc interstitial $\left({\text{Zn}}_i\right)$ , oxygen vacancy $\left(V_{\text{O}}\right)$ , and oxygen interstitial $\left({\text{O}}_i\right)$ defect levels, respectively. In contrast, the deep level emissions of metal organic chemical vapor deposition grown samples consisted of blue and green emissions and blue and orange-red emissions at low and high oxygen flow rates, respectively. The ZnO nanorods synthesized by thermal evaporation showed a dominant deep level emission at the green region, which is associated with oxygen vacancies $\left(V_{\text{O}}\right)$ .

V-defect formation of the ${\mathrm{In}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N/GaN}$ multiple quantum wells (MQWs) grown on GaN layers with different threading dislocation (TD) densities was investigated. From cross-sectional transmission electron microscopy, we found that all V defects are not always connected with TDs at their bottom. By increasing the indium composition in the ${\mathrm{In}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ well layer or decreasing the TD density of the thick GaN layer, many V defects are generated from the stacking mismatch boundaries induced by stacking faults which are formed within the MQW due to the strain relaxation. Also, TD density in the thick GaN layer affects not only the origin of V-defect formation but also the critical indium composition of the ${\mathrm{In}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ well on the formation of V defects.