Epitaxial Growth of GaN Core and InGaN/GaN Multiple Quantum Well Core/Shell Nanowires on a Thermally Conductive Beryllium Oxide Substrate.

Beryllium oxide (BeO) belongs to a very unique material family that exhibits the divergent properties of high thermal conductivity and high electrical resistivity. BeO has the same crystal structure as GaN, and the absolute difference in the lattice constants is less than 17%. Here, the growth of GaN nanowires (NWs) on the polycrystalline BeO substrate is reported for the first time. The NWs are grown by a vapor-liquid-solid approach using a showerhead-based metal-organic chemical vapor deposition. The growth direction of NWs is along the m-axis on all planes of the substrate, and it is confirmed by transmission electron microscopy (TEM) and selected area electron diffraction (SAED) patterns. The vertical and tilted growth of NWs is due to the different planes of the substrate such as the m-plane, a-plane, and semipolar planes and is confirmed by X-ray diffraction. Subsequently, the GaN shell and InGaN/GaN multiple quantum wells (MQWs) are coaxially grown using a vapor-solid approach in the same reactor. A very high crystal quality is verified by TEM and SAED and is also confirmed by measuring the photoluminescence. The optical emission is tuned for the entire visible spectrum by increasing the indium incorporation in InGaN quantum wells. The conformal growth of InGaN/GaN MQW shells and the defect-free nature of the structure are confirmed from spatially resolved cathodoluminescence. This study will provide a platform for researchers to grow GaN NWs on the BeO substrate for a range of optical and electrical applications.