Transmission electron microscopy study on pre-strained InGaN/GaN quantum wells

We use the techniques of high-resolution transmission electron microscopy and strain state analysis (SSA) to show the material nanostructures of two InGaN/GaN quantum-well (QW) samples. In one of the samples, a low-indium InGaN/GaN QW is grown before five high-indium ones, which are grown under the same conditions as those for growing the five QWs in another sample (the control sample). From the calibrations of the average indium contents of those QWs based on the SSA images, it is found that the QWs close to the low-indium one have higher indium contents than those in the control sample. Such an increase of indium incorporation is attributed to the pre-strain effect of the low-indium QW on the barrier layer right above it. The pre-strain effect diminishes along the growth of more QWs. This effect represents an effective approach for increasing indium contents for implementing yellow-red light-emitting diodes based on InGaN/GaN QW structures.