Low temperature MOCVD growth of V/VI materials via a Me/sub 3/SiNMe/sub 2/ elimination reaction

Abstract

ExperimentalThe reactive precursors M(NMe,), (M = Sb, Bi) and General Procedures (Me,Si),Te were used to deposit films of M,Te, (M = Sb, Si) on Si(l11) cut 4" off-axis, GaAs(l00), and Kapton substrates between 25°C and 150°C in a low pressure MOCVD reactor. The film growth process is a novel N,N-dimethylaminotrimethylsilane (Me,SiNMe,) elimination reaction and not pyrolysis reactions employed in conventional MOCVD techniques. X-ray diffraction data show the crystalline quality and orientation of the resulting polycrystalline films were dependent on the substrate structure and growth temperature. Amorphous films were deposited below 50°C. Films deposited at 75°C for Sb,Te, and 125°C for Bi,Te, were highly oriented with the (015) reflection plane parallel to the substrate surface. Films of Sb,Te, deposited at 150°C were highly oriented with the (OOt) reflection planes parallel to the substrate surface. The electrical properties and composition of Bi,Te, films deposited at 125°C on Kapton were independent of the VIVI precursor ratio used. Variation in the composition of a Sb,Bi,,Te, ternary film across the susceptor was observed due to differences in the reaction kinetics for formation of Sb,Te, and Bi,Te,. This unique deposition reaction provides an alternative route to prepare group V chalcogenide materials which have potential applications in solar cells, reversible optical storage, and thennoelectrics.Polycrystalline Sb,Te,, Bi,Te, and Sb,Bi,-,Te films were grown in a reduced pressure (20-100 torr) vertical MOCVD reactor with an inductively heated substrate stage using Sb(NMe,), andor Bi(NMe,), and (Me,Si),Te with prepurified H, as a carrier gas. The precursor vapors were isolated prior to entering the reactor using a coaxial inlet system which allowed the gas flows to mix 3cm above the center of the susceptor. In the first series of growth experiments, films were deposited simultaneously on GaAs( 100) (high resistivity Cr doped) and Si(ll1) substrates placed next to each other on the susceptor. The substrates were cleaned then etched with 5% HF solution for Si(ll1) and NH,OH/H,O, solution for GaAs prior to use. The only volatile byproduct identified by proton NMR (of reactor exhaust gases collected in a liquid nitrogen cooled trap) and the Residual Gas Analyzer (in situ monitoring of reactor exhaust) was Me,SiNMe,. The V N I inlet ratio was determined by integration of the peaks of Me,SiNMe, and any excess group V or (Me,Si),Te precursor in the HI NMR spectrum trapped byproducts. The surface morphologies of the films vary from smooth, highly reflective surfaces to dull gray. X-ray diffraction data used to characterize the structural phases and the crystalllinity of the deposited films was collected on a Scintag Pad V XRD