Growth defects in GaN films on sapphire: The probable origin of threading dislocations
- PDF / 989,722 Bytes
- 13 Pages / 612 x 792 pts (letter) Page_size
- 106 Downloads / 214 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Growth defects in GaN films on sapphire: The probable origin of threading dislocations X. J. Ning, F. R. Chien, and P. Pirouz Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, Ohio 44106
J. W. Yang and M. Asif Khan APA Optics, Inc., Blaine, Minnesota 55434 (Received 20 March 1995; accepted 20 November 1995)
Single crystal GaN films with a wurtzite structure were grown on the basal plane of sapphire. A high density of threading dislocations parallel to the c-axis crossed the film from the interface to the film surface. They were found to have a predominantly edge 1 character with a 3 k1120l Burgers vector. In addition, dislocation half-loops, elongated along the c-axis of GaN, were also found on the prism planes. These dislocations had a mostly screw character with a [0001] Burgers vector. Substrate surface steps with a 1 height of 6 cAl2 O3 were found to be accommodated by localized elastic bending of GaN (0001)GaN planes in the vicinity of the filmysubstrate interface. Observations show that the region of the film, with a thickness of ,100 nm, adjacent to the interface is highly defective. This region is thought to correspond to the low-temperature GaN “buffer” layer which is initially grown on the sapphire substrate. Based on the experimental observations, a model for the formation of the majority threading dislocations in the film is proposed. The analysis of the results leads us to conclude that the film is under residual biaxial compression.
I. INTRODUCTION
GaN is a wide band gap ( 3.39 eV) semiconductor and a promising candidate for the manufacture of light emitting diodes (LED’s) and laser diodes in the short wavelengths from blue to ultraviolet. In the last few years, it has become possible to grow single crystal films of GaN on various substrates by the techniques of metal-organic chemical vapor deposition (MOCVD)1 and molecular beam epitaxy (MBE).2,3 Because of the potential applications of GaN in optoelectronics, there has recently been a concerted effort to improve the quality of the films. Currently, the most common substrates for the growth of GaN films are the (0001) and s1100d surfaces of sapphire (a –Al2 O3 ) (for recent reviews, see Refs. 4 and 5). Structural characterization of GaN films grown under different growth conditions has also been carried out by a number of workers.3,6–10 The major defects that have been reported in these films are dislocations, double positioning boundaries (DPB’s), and inversion domain boundaries (IDB’s).3,6–8 However, there are still a lot of unanswered questions concerning the nature of the defects and the mechanisms by which they form. In this study, a thorough characterization of single crystal GaN films grown on the basal, (0001), plane of sapphire was carried out using different techniques of transmission electron microscopy (TEM). These include conventional electron diffraction, strain contrast imaging 580
http://journals.cambridge.org
J. Mater. Res., Vol. 11, No. 3,
Data Loading...
