Band Structure Engineering Based on InGaN/ZnGeN2 Heterostructure Quantum Wells for Visible Light Emitters

Band structure engineering based on InGaN/ZnGeN2 heterostructure quantum wells (QWs) is proposed to address the long-standing charge separation challenge in visible light emitters using polar InGaN QWs as active media. A nanometer-scale layer of ZnGeN2 is successfully incorporated in InGaN QWs via metalorganic chemical vapor deposition. Understanding the structural properties of the heterostructure QWs reveals that the growth conditions for the GaN barrier layers play an important role in the QW properties. Specifically, the structural quality of the QWs is improved by increasing the thickness and the growth temperature of the GaN barrier layers. Due to the large band offset at the InGaN/ZnGeN2 heterointerface, the position and thickness of the ZnGeN2 sub-layer within the InGaN QWs determine the potential minima and thus the carrier wave functions in both conduction and valence bands. This work demonstrates the effectiveness of emission wavelength tunability of InGaN/ZnGeN2/InGaN heterostructure QWs via tuning of the ZnGeN2 sub-layer properties. More significantly, the peak emission of InGaN/ZnGeN2/InGaN heterostructure QWs can be extended to longer wavelengths without increasing the In composition or the QW thickness. Results from this work provide a new route for addressing the low quantum efficiency of conventional InGaN QWs emitting at green and longer wavelengths.