Cathodoluminescence Study of InGaN/GaN Quantum-Well LED Structures Grown on a Si Substrate

Crack-free InGaN/GaN quantum-well (QW) light-emitting diode (LED) structures were grown on a patterned Si substrate. Spatially resolved cathodoluminescence was studied on these LED wafers. Cathodoluminescence (CL) emission spectra at room temperature and low temperature (82 K) were measured. A main LED peak (∼2.7 eV) and an additional peak (∼3.1 eV) in the emission spectra at 82 K were observed. Using CL spectra mapping measurements on a cross section of the sample, it can be clearly seen that the ∼3.1 eV emission comes from the interfacial layer between the p-AlGaN and the QWs. This observation was further verified by comparing spectra of specific points on the cross section by line scanning. The origin of such emission is discussed. Cathodoluminescence images, emission spectra, and x-ray energy dispersion spectra (EDS) showed that the In composition at a specific corner of the mesa was higher than that in the rest of the mesa. Such macroscopic inhomogeneity might be caused by gas dynamics on the patterned substrate.