ScAlMgO 4 : An Oxide Substrate for GaN Epitaxy
- PDF / 1,121,057 Bytes
- 4 Pages / 414.72 x 648 pts Page_size
- 71 Downloads / 205 Views
considered to be a superlattice of rock-salt-like layers and wurtzite-like layers. The oxygen lattice is near to close-packed. The smallest of the known YbFe2 0 4 -type materials, ScAlMgO 4 is well matched (+1.8%) to the hexagonal face of wurtzite-structure GaN. A more complete report of this work has been published elsewhere.[7] PREPARATION AND CHARACTERIZATION OF ScAlMgO 4 CRYSTALS Two types of ScAIMgO 4 substrate crystals were prepared and used for epitaxial growth. Platelets as large as 1 cm across were grown by slow cooling of a stoichiometric melt. A 50g batch prepared from stoichiometric amounts of MgO, Sc 20 3 and A12 0 3 was placed in an Ir crucible. The sample was melted using RF induction heating under an N 2 atmosphere. The sample was then cooled slowly to yield crystals approaching 1 cm diameter and 1 mm thick, although many of these had low angle grain boundaries. Flat flakes were peeled from the micaceous crystal mass and soldered with indium to molybdenum heater blocks for epitaxial growth. A compelling reason to consider ScAlMgO 4 as a potentially practical substrate for GaN epitaxial films is that it can be grown by the Czochralski method. Thus, the techniques needed to produce large diameter, high quality crystals on an industrial scale are already well established. A melt of stoichiometric composition was prepared by mixing 44.01g MgO and 75.3 1g Sc2 0 3 , forming the mixture into a pellet, placing the pellet into a conventional iridium crucible together with 55.68g A120 3 , and heating the charged crucible under N2 in a conventional RF induction furnace. The starting materials were commercially available, and of at least 99.99% purity. The charge was completely molten at about 1900'C. At this point, a thin iridium rod was dipped into the liquid and a button of polycrystalline ScAlMgO 4 was formed on the tip of the rod. 51 Mat. Res. Soc. Symp. Proc. Vol. 39510 1996 Materials Research Society
The rod with solidified ScAlMgO 4 thereon was slowly raised (initially at 2.5 mm/hr) and rotated at 15 rpm. After about 1.5 hours the pull rate was gradually increased to 4 mm/hr. Pull conditions were regulated under computer control by maintaining weight gain to yield a boule having a neck (about 7mm in diameter, about 60mm long) that blended smoothly into the main body of the boule, about 60mm long. This was done to favor the growth of a limited number of relatively large crystals in the boule. Away from the seed end of the boule, the crystallites were large enough to separate with a razor blade into 20mm diameter near-single crystal slices. The slices were then mounted on a polishing block with black wax and polished with emery paper until they were flat on a cleavage plane. The slices were flipped and the process repeated on the reverse side, followed by polishing of the intended growth surface with LINDE A®and LINDE B® polishing compound. The surface chips rather easily, so considerable care is required during this stage, so as not to gouge the surface. After a final polish using Syton®on polishing pa
Data Loading...
