Microstructure of Nonpolar a-Plane GaN Grown on (11 2 0) 4H-SiC Investigated by TEM.
- PDF / 1,962,963 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 12 Downloads / 202 Views
Y5.28.1
Microstructure of Nonpolar a-Plane GaN Grown on (1120) 4H-SiC Investigated by TEM. D.N. Zakharov1, Z. Liliental-Weber1, B. Wagner2, Z.J. Reitmeier2, E.A. Preble2, and R.F. Davis2 1 2
Lawrence Berkeley National Laboratory, MS 62-203, Berkeley, CA 94720 North Carolina State University, Raleigh, NC 27695
ABSTRACT Plan-view and cross-section samples of (1120) (a-plane) GaN grown on 4H-SiC substrates with AlN buffer layers were studied by transmission electron microscopy. Samples reveal the presence of a high density of stacking faults formed on the basal plane of hexagonal GaN. These stacking faults, terminated in the growth plane by threading dislocations, nucleate at the AlN/4H-SiC interface and propagate to the GaN layer surface. High resolution electron microscopy shows that the majority of stacking faults are low-energy planar defects of the type I1 and I2. High energy stacking faults (E) are not observed. INTRODUCTION III-V nitrides have received much interest as a promising material for laser diodes and light emitting diodes [1,2]. Commercially available GaN-based devices are usually grown on (0001) Al2O3 or 6H-SiC substrates. Recently it has been shown theoretically [3] and proven experimentally [4], that spontaneous and piezoelectric polarizations are present within GaNbased active layers. The total polarization aligned along [0001] direction of hexagonal GaN structure leads to high interface charge densities and spatial separation of electron and holes wave functions in quantum well structures, which alters the optoelectronic properties of devices. One of the possible solutions to eliminate these effects is to grow GaN-based layers in nonpolar orientations, such as {1100} (m-plane) or {1120} (a-plane). M-plane and a-plane GaN layers have been successfully grown on (100) LiAlO2 and r-plane Al2O3 respectively [5,6]. These layers indeed demonstrated polarization free behavior along the growth direction. Investigations of the above layers grown in nonpolar direction by transmission electron microscopy revealed high densities of basal stacking faults and threading dislocations [7,8]. The reason for their presence was not well understood. In order to explore defect issues in such polarization-free layers we performed structural studies by conventional and high resolution electron microscopy on a-plane undoped GaN layers grown on (1120) 4H-SiC. EXPERIMENTAL The AlN buffer layer and the GaN epilayer were sequentially grown on a 12mm x 12mm square 4H-SiC (1120) substrate in a cold-walled, vertical, pancake-style organometallic vapor phase epitaxy (OMVPE) system. The 100 nm thick AlN buffer layer and the 1µm thick undoped GaN layer were grown at 20 Torr at temperatures of 1100°C and 1015°C, respectively. The precursor species of Tri-methylaluminum, tri-ethylgallium and Ammonia with mass flow rates of 5.4 µmol/min, 101 µmol/min and 0.14 µmol/min, respectively were mixed with a high purity H2 (3 slm) in a two-inch internal diameter sleeve located two inches above the substrate.
Y5.28.2
Samples were studied b
Data Loading...
