Gas source molecular beam epitaxy of high quality AlGaN on Si and sapphire
- PDF / 236,959 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 39 Downloads / 208 Views
1
Gas source molecular beam epitaxy of high quality AlGaN on Si and sapphire. S. Nikishin, G. Kipshidze, V. Kuryatkov, A. Zubrilov1 , K. Choi, Ìu. Gherasoiu, L. Grave de Peralta, T. Prokofyeva2, M. Holtz2, R. Asomoza3, Yu. Kudryavtsev3 and H. Temkin Department of Electrical Engineering, Texas Tech University, Lubbock, TX 79401, USA; 1 Ioffe Physical-Technical Institute, St. Petersburg, 194021, Russia; 2 Department of Physics, Texas Tech University, Lubbock, TX 79401, USA; 3 SIMS laboratory of SEES, Department of Electrical Engineering, CINVESTAV, Mexico D.F. 07300, Mexico
ABSTRACT We report the results of epitaxial growth experiments on AlxGa1-xN (0≤ x ≤ 1) on Si(111) and sapphire substrates aimed at understanding the origin and elimination of cracking. We describe growth procedures resulting in thick layers of AlxGa1-xN, grown by gas source molecular beam epitaxy with ammonia, that are free of cracks. In GaN layers with the thickness of ~2.5 µm, we find the background electron concentration of (1-2)×1016 cm-3 and mobility of (800±100) cm2/Vs. In AlxGa1-xN (0.2 < x < 0.6) with the film thickness of 0.5-0.7 µm the electron concentration of (2-3)×1016 cm-3 is obtained. Low background concentrations in GaN allow for formation of p-n junctions by doping with Mg. Light emitting diodes with the peak emission at 380 nm have been demonstrated. INTRODUCTION Considerable progress has been shown recently in the growth of nitride-based layers and structures using molecular beam epitaxy (MBE) [1-7]. In particular, gas source MBE (GSMBE) with ammonia allows for the growth of nitrides at high temperatures needed to assure devicequality layers [8-10]. However, the processes of crack formation in AlGaN, the p-dopant incorporation, and the detailed bandgap dependence on composition are still not well understood. Two growth nucleation methods are known to be effective in the preparation of epitaxial nitride layers on Si substrates. In the first, growth is carried out on the Si(111)-7 x 7 reconstructed surface [11-14], at temperatures below 830oC. The procedure includes deposition of a few monolayers of Al on the Si surface before the growth of AlN, to prevent formation of amorphous SiNx. After that, the Al layer is nitrided and epitaxy of AlN is initiated. In the second approach, AlN is formed at a temperature higher than that of the 7x7 to 1x1 surface reconstruction transition at 830oC. This approach, used in the work discussed here, relies on formation of a Si-N-Al interlayer and the subsequent epitaxy of AlN [15]. The nucleation of AlN on sapphire follows established procedures [16]. Aside from differences in nucleation, the same growth process was used for the growth of AlGaN on Si(111) and sapphire (0001). EXPERIMENTAL DETAILS Layers of AlxGa1-xN with 0≤x≤1 were grown by GSMBE with ammonia on oriented n- and p-type Si(111) substrates prepared by wet chemical etching [15] and on sapphire substrates. The effects of growth conditions on the surface morphology, uniformity of the film thickness, and the structure of epitaxial layers
Data Loading...
