Growth of hexagonal GaN thin films on Si(1 1 1) with cubic SiC buffer layers

Abstract

The growth of GaN films on silicon or sapphire substrates has not been straightforward due to their large mismatch (>13%). SiC is structurally the closest material to GaN (especially cubic form) and has a small lattice mismatch (3.5%) between SiC and GaN, and therefore can be useful as the substrate for GaN. Single-crystal wafers of cubic SiC and GaN, however, are hard to obtain and have not been produced commercially yet. Therefore, a thin layer of cubic SiC on substrates such as Si and oxide single crystals might solve this problem and will be one of a suitable buffer layers for the cubic GaN film growth. Epitaxial cubic SiC buffer layers were grown on either carbonized or uncarbonized Si(111) substrates as low as temperature of 830°C using a supersonic molecular jet of t-butyldimethylsilane, (CH3)3CSiH(CH3)2, and the polycrystalline hexagonal GaN thin films were subsequently deposited on them at 600°C using a MOMBE system. The buffer layers and the GaN films were characterized by AES, XRD, FTIR, ellipsometry, and X-ray phi(φ)-scan measurements. The growth temperature of t-butyldimethylsilane was much lower than conventional CVD growth temperatures and this is the first report to obtain epitaxial cubic SiC films on Si from t-butyldimethylsilane and new attempt to grow h-GaN thin films on cubic SiC buffer layers.