Surface Instability and Associated Roughness of Pendeo-epitaxy GaN (0001) Films Grown via Metalorganic Vapor Phase Epita
- PDF / 388,184 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 76 Downloads / 142 Views
Surface Instability and Associated Roughness of Pendeo-epitaxy GaN (0001) Films Grown via Metalorganic Vapor Phase Epitaxy Amy M. Roskowski*, Peter Q. Miraglia, Edward A. Preble, Sven Einfeldt**, and Robert F. Davis Department of Materials Science and Engineering, North Carolina State University Raleigh, NC 27695 *Department of Chemical Engineering, North Carolina State University Raleigh, NC 27695 **On Postdoctoral leave from the Institute of Solid State Physics, University of Bremen ABSTRACT A growth process route that results in thin film GaN templates with a smooth surface morphology at the optimum temperature of 1020ºC has been developed. Atomic force microscopy (AFM) reveals hillocks on films grown above 1020ºC. Hillocks resulted from the rotation of heterogeneous steps formed at pure screw or mixed dislocations which terminated on the (0001) surface. Growth of the latter feature was controlled kinetically by temperature through adatom diffusion. The 106 cm-2 density of the hillocks was reduced through growth on thick GaN templates and regions of pendeo-epitaxy (PE) overgrowth with lower pure screw or mixed dislocations. Smooth PE surfaces were obtained at temperatures that reduced the lateral to vertical growth rate but also retarded hillock growth that originated in the stripe regions. The ( 1120 ) PE sidewall surface was atomically smooth, with a root mean square roughness value of 0.17 nm which was the noise limited resolution of the AFM measurements. INTRODUCTION Selective overgrowth techniques including lateral epitaxial overgrowth (LEO)[1-3] and pendeo epitaxy (PE)[4, 5] have been used to grow GaN films with significantly lower concentrations of threading dislocations than conventional GaN on sapphire and SiC substrates. Pendeo-epitaxy involves the lateral and, commonly, the vertical growth of cantilevered “wings” of GaN from the sidewalls of etched GaN stripes with or without top masks, respectively[6]. The latter, referred to as “maskless PE”, has been the focus of this investigation. The time for coalescence of the laterally growing surfaces is reduced by increasing the temperature. However, it will be shown in the following sections that the use of elevated temperatures concomitantly enhances hillock growth and consequent surface roughening. The purpose of this research has been to investigate the origin of the afore mentioned surface roughening in GaN thin films used as templates for the subsequent growth of GaN or other nitride films, with the goal of developing growth process routes that produce a smooth surface morphology. Surface roughening was determined to be a function of hillock growth, which was associated with adatom site preference for heterogeneous steps associated with dislocations having screw character that intersect at the surface. The site preference for adatom incorporation of the reactant species on the surface of the growing film was controlled kinetically through temperature. Elevated temperatures promoted and sustained the growth of hillocks on the (0001) plane and enhanced th
Data Loading...
