Single Crystal Wurtzitic Aluminum Nitride Growth on Silicon Using Supersonic Gas Jets
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ABSTRACT Highly oriented aluminum nitride (0001) films have been grown on Si(001) and Si(111) substrates at temperatures between 5500 C and 7750 C with dual supersonic molecular beam sources. Triethylaluminum (TEA;[(C 2Hs)3AI]) and ammonia (NH 3 ) were used as precursors. Hydrogen, helium, and nitrogen were used as seeding gases for the precursors, providing a wide range of possible kinetic energies for the supersonic beams due to the disparate masses of the seed gases. Growth rates of AIN were found to depend strongly on the substrate orientation and the kinetic energy of the incident precursor; a significant increase in growth rate is seen when seeding in hydrogen or helium as opposed to nitrogen. Growth rates were 2-3 times greater on Si(001) than on Si(lll). Structural characterization of the films was done by reflection high energy electron diffraction (RHEED) and x-ray diffraction (XRD). X-ray rocking curve (XRC) full-width half-maxima (FWHM) were seen as small as 2.50. Rutherford back scattering (RBS) was used to determine the thickness of the films and their chemical composition. Films were shown to be nitrogen rich, deviating from perfect stoichiometry by 10%-20%. Surface analysis was performed by Auger electron spectroscopy (AES). INTRODUCTION Aluminum nitride is a promising candidate for use as a high energy photon emitter and solar-blind photodetector due to its large direct bandgap [1]. It also holds promise as a barrier material in microelectronics applications. The majority of the growth studies, motivated by the photo-coupling applications, have been on sapphire [2]. Using aluminum nitride as a barrier material, however, requires high quality growth on silicon substrates in order to find use in the majority of current microcircuitry technologies. Direct epitaxy of AIN on silicon is complicated by the large lattice mismatch (23%) causing AIN films to have high dislocation densities and broad XRD features. It has been shown that epitaxial hexagonal aluminum nitride can be grown on silicon with orientations of AlN(0001)IISi(001) [3], AIN(0001)IISi(111) [4], AlN(0110)IlSi(ll) [5], and AIN(1210)HlSi(110) [6]. Studies on the dependence of film quality and growth rate on microscopic molecular dynamics have not been reported.
EXPERIMENTAL PROCEDURE Growth is performed on both Si(001) and Si(l11) substrates. Prior to insertion into vacuum, the substrates are cleaned in a spin-processor. A cleaning cycle consists of degreasing
319 Mat. Res. Soc. Symp. Proc. Vol. 395 01996 Materials Research Society
with ethanol, oxide etching with a 10% HF solution, and an ethanol rinse. Immediately following chemical cleaning, the silicon is inserted into a load-locked turbo pumped sample preparation chamber (base pressure lxl0-1' Torr). Further in vacuo cleaning is done through 3 cycles of a 1 keV neon sputter followed by a 1000 K anneal. AES is used to confirm surface cleanliness. RHEED patterns taken at room temperature of cleaned Si(llI) and Si(001) substrates show clear evidence of 7x7 and 2x1 reconstruction, furthe
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