Oxygen and Sulfur Adsorption Effects on Electronic States of GaAs(100) Surfaces Studied with Discrete VariationalXα Method

Studies of Effects of Adsorption of Silicon or Germanium on the Electronic States of (100) GaAs Surfaces

“…Their favorable effect on both Ga-and Asterminated surfaces suggests that the properties of group IV elements are more suitable than S (group VI element), which does not reduce the density of the surface states when applied to an As-terminated surface. 8) The results of our calculations give theoretical support to the good experimental results that have been reported by Koyanagi et al 5) and Xie et al 6) They demonstrated the very clear favorable effects of using Si interface-control layers to suppress the density of the gap states. Another merit of Si and Ge is their adsorption heights.…”

“…In that case, adsorption on a Ga-terminated surface is much more stable than adsorption on an As-terminated surface. 8) The most stable adsorption heights are 1.486…”

“…The reduction in the in-gap DOS due to Si is more significant than that caused by S. 8) One effect that is quite different from S-adsorption is that Si very effectively reduces the density of the gap states of an As-terminated surface. The S-As anti bonding orbital generates a peak of states in the band gap, 8,9) whereas in a Siadsorbed As-terminated surface, the bonding orbital lies in the valence band and the anti bonding orbital lies in the conduction band, so consequently the density of the in-gap states becomes very low. Therefore, Si passivates both Gaand As-terminated surfaces.…”

“…Seto et al 10,16) reported that O adsorbs at the bridge sites of a Ga plane with an extremely low height (nearly zero) and generates a high stress, which very possibly generates defects or disorders, although whether the stress is accumulated or relaxed depends on the details of the bond structure between O and Ga. 16) Si and Ge, as well as S, Te, Se (passivation effect of these were reported), stably bind with the surface Ga or As atoms with heights of more than 1 A, and hence have little influence on the tetrahedral symmetry of (100) GaAs as compared with O. 8,10) This suggests that both Si and Ge are effective materials from this point of view too. They bind with surface Ga or As atoms without strongly distorting the tetrahedral symmetry.…”

Relationships between Interface Structures and Electrical Properties in the High-k/III–V System

“…Figure 8(c) shows P 2s photoelectron spectra for the InP surfaces after NH 4 OH etching and deposition of Al 2 O 3 layers 1.0 or 2.5 nm thick. From the chemical point of view, As-O bonds are covalent bonds between atoms in the second and fourth rows of the Periodic Table. Since the HOMO-LUMO gap of such bonds are predicted to be rather small, the LUMO states of the interfacial As-O bonds are among the possible origins of the gap states [26]. The difference in behaviors between PO x and AsO x is ascribed to the difference in their bond strengths.…”