Structural properties of maskless epitaxial lateral overgrown MOCVD GaN layers on Si (1 1 1) substrates

We report on the maskless epitaxial lateral overgrowth of GaN on structured Si (1 1 1) substrates and on its structural properties using transmission electron microscopy and photo-electrochemical (PEC) etching techniques. The structured silicon substrates are achieved using photolithography and dry etching; 4-µm-deep holes of 1.5 µm in diameter, each separated by 2.5 µm, are etched in the (1 1 1) Si surface. The growth process is started by depositing a 10-nm-thick AlN buffer layer at 850°C and then followed by the growth at high temperature (1170°C) of the GaN epilayer. The deposition of GaN takes place first on the Si (1 1 1) surface covered with AlN in between the holes, i.e. no deposits are formed in the holes. During the growth the GaN layer extends vertically and laterally over the holes until complete coalescence. Transmission electron microscopy shows that regions over the holes only contain dislocations in the basal plane resulting from the bending of dislocations nucleated at the Si/AlN interface and at the coalescence boundary between the two laterally overgrown layers. This results in a drastic decrease of dislocation density in these areas of the films. The revelation of dislocations is also achieved by PEC etching technique