| Abstract Scope |
Achieving low interface trap densities and low equivalent oxide thicknesses are still considered major challenges in the development of III-V MOSFETs. Numerous studies have investigated the influence of surface treatment prior to high-k deposition on these parameters. Here we investigate the influence In<SUB>0.53</SUB>G<SUB>0.47</SUB>As surfaces exhibiting different surface reconstructions with trimethylaluminum (TMA) prior to HfO<SUB>2</SUB> gate dielectric deposition using chemical beam epitaxy. Interface trap densities and Fermi level efficiency of the gate stacks were analyzed using the conductance and Terman methods. Surfaces of As-decapped In<SUB>0.53</SUB>G<SUB>0.47</SUB>As layers on (001) InP were exposed to TMA for short times at substrate temperatures between 200 and 300 °C. The growth surfaces were monitored using reflection high-energy electron diffraction (RHEED). It is shown that the TMA dose, exposure time and substrate temperature critically influence the electrical properties of the gate stack, despite that fact that the TMA exposure was sufficiently short to have no apparent influence on the surface reconstructions seen in RHEED. For (2x4) reconstructed In<SUB>0.53</SUB>G<SUB>0.47</SUB>As surfaces TMA acted as surfactant, allowing for the growth of thin, coalesced HfO<SUB>2</SUB> films using hafnium tert-butoxide as the source. These stacks could be scaled to equivalent oxide thicknesses of less than 1 nm. Without prior TMA exposure the HfO<SUB>2</SUB> films grew columnar and were not coalesced up to 30 nm in thickness. For low TMA doses and in combination with post-deposition anneals in forming gas, interfaces with an unpinned Fermi level were obtained, showing a band bending corresponding to more than half of the band gap of In<SUB>0.53</SUB>G<SUB>0.47</SUB>As [1]. For higher substrate temperatures and longer TMA exposure times, a much more pronounced midgap interface trap response was observed. For these stacks, the Fermi level was pinned near midgap even after forming gas anneals. For the group-III-rich, (4x2) reconstructed In<SUB>0.53</SUB>G<SUB>0.47</SUB>As surfaces, TMA had no effect on the growth of HfO<SUB>2</SUB> films and did not act as a surfactant. We will discuss the mechanisms by which TMA and forming gas control the interface trap densities and Fermi level (un)pinning. <I>[1] Y. Hwang, R. Engel-Herbert, N. G. Rudawski, S. Stemmer, Effect of post-deposition anneals on the Fermi level response of HfO<SUB>2</SUB>/In<SUB>0.53</SUB>G<SUB>0.47</SUB>As gate stacks, J. Appl. Phys. 108, 034111 (2010).</I> |