Process Routes for Low Defect-Density GaN on Various Substrates Employing Pendeo-Epitaxial Growth Techniques
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Mat. Res. Soc. Symp. Proc. Vol. 537 © 1999 Materials Research Society
tailored microstructure comprised of forms previously etched into the seed layer. Continuation of the pendeo-epitaxial growth until coalescence over and between these forms results in a complete layer of low defect-density GaN. This is accomplished in one regrowth step, and the need to align devices or masks for the growth of a second layer over particular areas of overgrowth on the final GaN layer is eliminated. This approach may be more widely applicable than just GaN, as indicated by Gehrke et.al. [15]. Additionally, we report for the first time the ability to grow GaN pendeo-epitaxial films on silicon substrates. The achievement of GaN layers with surface areas limited only by the size of the available silicon substrates is now conceivable. The following sections describe the experimental parameters necessary to achieve GaN films via PE, describe and discuss the microstructural evidence obtained for the resulting films and provide a summary of this research.
EXPERIMENTAL PROCEDURES Each pendeo-epitaxial GaN film and the underlying GaN seed layer and the AIN buffer layer were grown in a cold-wall, vertical pancake style RF inductively heated metallorganic vapor phase epitaxy (MOVPE ) system. Two distinct process routes were explored for growth on (i) on-axis (0001)6H-SiC substrates and (ii) on-axis (I I1)Si substrates. In the former, each seed layer consisted of a 1 jim thick GaN film grown on a 100 nm thick AIN buffer layer previously deposited on a (0001) 6H-SiC substrate. Details of the experimental parameters used for the growth of these two layers are given in Ref. 13. In the growth on the Si substrates, a 1 gm (111)3C-SiC film was initially grown on a very thin (I I )3C-SiC layer produced by conversion of the (Il l)Si surface via reaction with C3 H8 entrained in H2 . Both the conversion step and SiC film deposition were achieved using a cold-wall, vertical geometry, RF inductively heated atmospheric pressure chemical vapor deposition (APCVD) reactor. Details of the experimental parameters used for the conversion step and the growth of the 3C-SiC layer are given in Ref. 14. A 100 nm thick AIN buffer layer and a 1 gm GaN seed layer were subsequently deposited in the manner used for the 6H-SiC substrates and noted above. A 100 nm silicon nitride growth mask was deposited on the seed layers via plasma enhanced CVD. A 150 nm nickel etch mask was subsequently deposited using e-beam evaporation. Patterning of the nickel mask layer was achieved using standard photolithography techniques followed by dipping in HNO 3 for approximately five minutes. The samples were subsequently cleaned by consecutive dips in trichloroethylene, acetone, methanol, and HCI for five minutes each and blown dry with nitrogen. The final, tailored, microstructure consisting of seed forms was fabricated via removal of portions of the nickel etch mask via sputtering and by inductively coupled plasma (ICP) etching of portions of the silicon nitride growth mask, the GaN se
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