Investigation of electron energy states in InGaN/GaN multiple quantum wells

Blue light emitting diodes (LED) consisting of InGaN/GaN multiple quantum wells (MQWs) have been grown by metal organic chemical vapor deposition (MOCVD) on sapphire. The width of the quantum wells (InGaN) was maintained in the range of 3–5 nm with a barrier of 10–15 nm of GaN. Various diagnostic techniques were employed for the characterization of the InGaN/GaN heterostructure. Carrier concentration depth profile from C–V measurements demonstrated the presence of MQWs. The higher value of built-in voltage (15 V) determined from C⁻²–V plot also supported the presence of MQWs as assumed to alter the space-charge region width and hence the intercept voltage. Arrhenius plots due to DLTS spectra from the device revealed at least four energy states (eV) 0.1, 0.12, 0.15 and 0.17, respectively in the quantum wells, with respect to the barrier. Further the photoluminescence spectrum showed an InGaN-based broad band centered at 2.9 eV and the GaN peak at 3.4 eV. A comparison of the PL spectrum with the literature helped to estimate the indium content in the QW (InGaN) and its width to be ∼13% and ∼3 nm, respectively. The results were consistent with the DLTS findings.