Embedded voids approach for low defect density in epitaxial GaN films

Abstract

We have developed a technique for defect reduction in GaN epitaxial films grown on sapphire substrates. This technique relies on the generation of high densities of embedded microvoids (∼108/cm2), a few microns long and less than a micron in diameter. These voids are located near the sapphire substrate, where high densities of dislocations are present. Network of embedded voids offer free surfaces that act as dislocation sinks or termination sites for the dislocations generated at the GaN/sapphire interface. Both transmission electron and atomic force microscopy results confirm the uniform reduction of the dislocation density by two orders of magnitude.

Overgrowth of GaN on GaN nanowires produced by mask-less etching

“…The dislocation densities deduced from XRD, shown in Fig. 8, are higher than what we previously reported using TEM and AFM techniques [10]. Both TEM and AFM give estimates of dislocation density in the overgrown GaN film on the nanowires, indicating the real defect density of these overgrown GaN films.…”

“…The exact process and recipe has been reported elsewhere [10,11]. The 1st generation of overgrown GaN EVA film is then put through another process of EVA overgrowth using it as a template material to be etched.…”

“…GaN nanowires are formed by a mask-less ICP-RIE technique that is believed to be based on the presence of a high density of dislocations present in the starting GaN film [10]. The mechanism of preferential etching the areas of threading dislocations is shown in Fig.…”

“…This EVA technique is capable of reducing the dislocation density (in our films) from 10 9 /cm À 2 by two orders of magnitudes; achieving dislocation densities in the 10 7 /cm À 2 range [10,11]. EVA is based on the overgrowth of GaN on GaN nanowires.…”

“…thick) were grown on (0001) sapphire substrates, and then etched in a Trion Minilock system by the Inductively-coupled Plasma Reactive Ion-Etching (ICP-RIE) technique to obtain nanowires. For GaN etching, a gas mixture of Cl 2 (27 sccm) and BCl 3 (5 sccm) have been used with ICP/RIE powers of 300/100 W respectively at a pressure of 2 Pa. Overgrowth by EVA was carried out again using MOCVD and these procedures have been reported elsewhere [10,11]. High Resolution Scanning Electron Microscopy (HRSEM), Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) were used for the characterization of the initial films and the etched nanowires as well as for the overgrown films.…”