Chemical beam epitaxy of GaN on Si (111) using AlAs buffer layers

The chemical beam epitaxy of GaN on Si (111) using an AlAs buffer layer has been investigated. Transmission electron microscopy of cross-section samples reveals a nanoscale columnar structure consisting of the hexagonal GaN polytype. Selected area diffraction indicates an epitaxial relationship between the GaN and Si substrate which is described by GaN [0001] parallel Si [111] and GaN (11-bar 00) parallel Si (112-bar). Raman spectroscopy of the samples shows that the AlAs longitudinal optical (LO) and transverse optical (TO) modes are observed at 360 and 400 cm-1, respectively, and that the GaN E2 TO and A1 LO modes occur at 562 and 733 cm-1, respectively. Raman peaks between 616 and 673 cm-1 are attributed to an interlayer of AlN formed by the nitridation of the AlAs buffer layer. (author)