Growth optimization for high quality GaN films grown by metal-organic chemical vapor deposition
- PDF / 715,966 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 73 Downloads / 252 Views
1068-C03-08
Growth optimization for high quality GaN films grown by metal-organic chemical vapor deposition Jung Hun Jang, A M Herrero, Seungyoung Son, B Gila, C Abernathy, and V Craciun Materials Science and Engineering, University of Florida, Gainesville, FL, 32611 ABSTRACT GaN layers were grown on c-plane sapphire substrates by using a conventional two step growth method via metal organic chemical vapor deposition (MOCVD). The effect of different growth conditions used in the deposition of the low temperature nucleation layer and high temperature islands growth on the crystalline quality of the GaN layers was investigated by high resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM). The polar (tilt) and azimuthal (twist) spread were estimated from the full width at half maximum (FWHM) values of the omega rocking curves (ω-RCs) recorded from planes parallel and perpendicular to the sample surface, respectively. It was found from the XRD and TEM study that the edge and mixed type threading dislocations were dominant defects so that the relevant figure of merit (FOM) for the crystalline quality should be considered only by the FWHM value of ω-RC of the surface perpendicular plane. The results showed that the mixed- and edge-types dislocation densities were strongly influenced by the growth conditions used in the deposition of the nucleation layer and high temperature islands growth. INTRODUCTION High quality GaN film has been obtained by a two-step growth method in which about 20 nm thick nucleation layer (NL) was deposited at low temperature (LT), followed by high temperature (HT) island growth [1,2]. The growth conditions, such as process temperature, TMGa flow rate, V/III ratio and chamber pressure used in each growth step, have a strong influence on the microstructure of the final GaN films. Figge et al. reported that the number of the nucleation sites during the nucleation layer deposition could be controlled by using V/III ratio [3]. Wood et al. showed the effect of nucleation layer annealing temperature and buffer layer growth temperature on their microstructure and morphology [4]. This work on the growth optimization has been carried out in order to find where the threading dislocations are generated from and how they can be reduced. EXPERIMENT The GaN films were grown on c-plane sapphire substrates using a Veeco P75 vertical MOCVD reactor via a conventional two-step growth method [1,2]. Trimethylgallium (TMGa), ammonia (NH3), and hydrogen (H2) were used as the Ga and N precursors, and carrier gas, respectively. The growth process was monitored by the reflectance transient method [5]. A 20 nm thick GaN nucleation layer (NL) was grown initially at 532~550 . Then, the temperature was ramped up to 1028-1096 for high temperature three-dimensional (3D) islands growth. The growth conditions for the high temperature islands and low temperature nucleation layer were controlled by changing TMGa flow rate with the same V/III ratio and growth temperature,
℃
℃
which was shown in table I.
Data Loading...
