Epitaxial growth of AlGaN/GaN HEMTs on patterned Si substrate for high voltage power switching applications

In this work, a series of AlGaN/GaN high electron mobility transistors (HEMTs) have been grown on patterned (Al)GaN-on-Si seed layers by metalorganic chemical vapor deposition (MOCVD) to study the effect of the (Al) GaN buffer thickness and its aluminum content on the vertical breakdown voltage. The atomic force microscopy (AFM) analysis performed on the GaN seed layers shows a perfectly smooth, MOCVD-like morphology with a threading dislocation density (TDD) around 2 x 109 cm 2. We succeeded to regrow up to 10 mu m and 5 mu m crack -free GaN + HEMT and Al0.30G0.70N + HEMT structures, respectively and scanning electron microscopy (SEM) revealed limited lateral growth on mesas with few microscopic defects while AFM show the same surface morphology of HEMT structures as ones grown on planar substrates. NiAu Schottky contacts were deposited on the regrown (Al)GaN HEMTs as well as on (Al)GaN seed layer structures. No breakdown was noticed up to 200 V for the regrown Al0.30Ga0.70N (3 mu m) HEMT and the GaN seed layer structures and the leakage current remained in the range of 1 nA. However, the leakage current in the regrown GaN (5 mu m) structure reached rapidly 1 mA. Such a high leakage was not noticed for non-patterned devices. Thus, it is possibly attributed to silicon contamination in the regrown GaN layer. On the other hand, the absence of noticeable leakage in the regrown 3 mu m thick Al-rich AlGaN buffer HEMT opens the way to a new competitive solution for high power electronics applications on silicon substrate.