Andreas Waag

Nanoscopic insights into the structural and optical properties of a thick InGaN shell grown coaxially on GaN microrod (Conference Presentation)

We present a nanometer-scale correlation of the structural, optical, and chemical properties of InGaN/GaN core-shell microrods. The core-shell microrods have been fabricated by metal organic vapor phase epitaxy (MOVPE) on c-plane GaN/sapphire templates covered with a SiO2-mask. The MOVPE process results in a homogeneous selective area growth of n-doped GaN microrods out of the mask openings. Surrounding the n-GaN core, a nominal 5 nm thick GaN shell and 30 nm thick InGaN layer were deposited. nHighly spatially resolved cathodoluminescence (CL) directly performed in a scanning transmission electron microscope (STEM) was applied to analyze the selective Indium incorporation in the thick InGaN shell and the luminescence properties of the individual layers. Cross-sectional STEM analysis reveal a hexagonal geometry of the GaN-core with m-plane side-walls. Directly at the corners of the hexagon a-plane nano-facets with a length of 45 nm are formed. The overgrowth of the GaN core with InGaN leads to a selective formation of Indium-rich domains with triangular cross-section exactly at these nano-facets as evidenced by Z-contrast imaging. Probing the local luminescence properties, the most intense CL emission appears at the m-plane side-facets with 392 nm peak wavelength. As expected, the Indium-rich triangles emit a red-shifted luminescence around 500 nm.

Recent progress in device-oriented II-VI research at the University of Wuerzburg

Interest in CdTe field effect transistors and multi-gated devices stems from the fact that CdTe is lattice matched to HgCdTe. As a consequence it may be possible to develop a monolithic technology that combines HgCdTe infrared focal plane arrays with on-board signal processing based on CdTe devices. Although CdTe metal-semiconductor field effect transistors have only recently been fabricated rapid improvement in device performance has been achieved. All the devices reported have been fabricated from CdTe:In epilayers grown by Photoassisted Molecular Beam Epitaxy. We report on devices having gold Schottky barrier with reverse breakdown voltages as high as 28. 0 V and ideality factors near 1. 7. These MESFETs exhibit good depleting mode action.