Group III-nitride (Al-, In-, Ga-, N) material system has been well studied and widely applied in optoelectronics such as light emitting diodes (LEDs) for solid state lighting. In contrast, the group II-IV-nitride is rarely studied, yet it can expand the material properties provided by III-nitrides. For example, ZnGeN2 has a similar bandgap and lattice constant as those of GaN. Recently, theoretical studies based on first principle calculation indicate a large band offset between GaN and ZnGeN2 (Delta_Ec=1.4 eV; Delta_Ev=1.5 eV). Utilizing the novel heterostructures of GaN (InGaN)/ZnGeN2, we studied the following two types of device structures: 1) Type-II InGaN-ZnGeN2 quantum wells (QWs) for high efficiency blue and green LEDs; 2) Lattice-matched GaN-ZnGeN2 coupled QWs for near-IR intersubband transitions. The design of type-II InGaN-ZnGeN2 QWs leads to a significant enhancement of the electron-hole wavefunction overlap due to the strong confinement of the holes in the ZnGeN2 layer as well as the engineered band bending. Simulation studies based on a self-consistent 6-band k∙p method indicate an enhancement of 5-7 times of spontaneous emission rate for an appropriately designed type-II InGaN-ZnGeN2 QWs for LED applications. For the coupled QW structure, it is comprised of two GaN QWs separated by a thin ZnGeN2 barrier layer, with thick ZnGeN2 layers as outer barriers surrounding the QWs. Our studies indicate that with optimized ZnGeN2 barrier thickness, the energy separation between E1 and E2 can be tuned to 92 meV for the resonance of the electron and LO-phonon scattering.
Hongping Zhao and Lu Han, "Novel device designs enabled by lattice-matched GaN-ZnGeN2 heterostructures (Conference Presentation)," Proc. SPIE 10104, Gallium Nitride Materials and Devices XII, 101041W (Presented at SPIE OPTO: February 02, 2017; Published: 19 April 2017); https://doi.org/10.1117/12.2252185.5391659261001.
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