Surface and interface states on GaAs(110): Effects of atomic and electronic rearrangements

Abstract

Research during the last year has led to a better understanding of the electronic and atomic structure of the (110) surfaces of III–V semiconductors. In this paper we will briefly review these new developments as well as point out areas where agreement has been found between various experimental results presented in the literature. It is now generally agreed that there are no intrinsic surface states in the band gap on GaAs and the smaller band-gap materials (e.g., GaSb, InAs, and GaSb) and that Schottky barrier pinning must be due to states produced when the metal adlayer is applied. Particular attention is focused in this paper on the large surface rearrangement which takes place on the (110) GaAs surface and effects of the strain which may be produced in joining this rearranged surface layer to the rest of GaAs crystal. It is pointed out that this may lead to variations in the surface rearrangement which can produce variations in the valence electronic structure at the surface. Such variations are shown in experimental energy distribution curves obtained by the photoemission technique which samples principally the last two molecular layers. It is further shown that surprisingly small amounts of chemisorbed oxygen can produce first-order effects in the valence-band electronic structure. On all GaAs (110) surfaces studied, a phaselike transformation was observed with a few hundredths of a monolayer coverage of chemisorbed oxygen. Near this coverage, the Ga 3d exciton structure disappears and the oxygen uptake increases significantly. On certain samples, first-order changes in the valence-band electronic structure were observed at a coverage of a hundredth of a monolayer or lower. These transformations are discussed in terms of the electronic and atomic configurations at the surface. Experimental data showing As and Ga 3d chemical shifts for oxidation as well as chemisorption are also presented and used to point out difficulties to be expected in passivating practical surfaces. In particular, the effect of mixed As and Ga oxides, the desirability of bonding passivating layers to the GaAs through As bonds, and the effect of strain-induced interface states are discussed.

Etude de diodes Schottky réalisées sous ultra-vide par dépôt d'aluminium ou d'argent sur GaP type N clivé

“…Un exemple des caractéristiques 1 (V ) que nous avons obtenues sur des surfaces clivées vierges d'un échantillon de dopage 8 x 1017 cm-3 est donné figure 3. Il montre que les extra courants sont devenus très importants pour les deux métaux.…”

“…Appl. 24 (1989) [45][46][47][48][49][50] décennies, a permis une avancée importante dans la compréhension de l'interaction métal-semiconducteur, en particulier dans le cas des composés III-V. Ces matériaux, outre leur intérêt technologique lié à la largeur de leur bande interdite ou à leur mobilité, peuvent présenter une surface exempte d'état électronique dans la bande interdite : c'est la surface (110) obtenue par clivage [3][4][5]. Il a ainsi été démontré que l'interaction de ces surfaces avec un métal (ainsi d'ailleurs qu'avec des atomes non métalliques) produit, dès les premiers stades du dépôt, un ancrage du niveau de Fermi qui explique en grande partie la valeur de la barrière 4>B mesurée dans les diodes Schottky [6][7][8][9].…”

Interfacial properties of metal–insulator–semiconductor capacitors on GaAs(110)

“…Such a high interface state density leads to surface Fermi level pinning which makes it impossible for making devices with optimal operation characteristics. 14 In contrast to GaAs ͑100͒, GaAs ͑110͒ can have a flat band up to the surface, 16,17 indicating the absence of both filled and empty surface states in the band gap. In short, it is found that a Si or Ge thin overlayer can form a heterojunction with GaAs and lower Schottky barrier heights 12,15 or unpin the GaAs surface Fermi level, while sulfur is effective in suppressing oxide formation and forming a stable S-Ga bond terminated surface.…”

Table_1.DOCX

“…Theoretical calculations show that intrinsic surface state density of GaAs is determined by the surface atom structure (Ivanov et al, 1980) and is highly dependent on the orientation. For example, the {110} surface is free of intrinsic mid-gap surface states (Spicer et al, 1977) whereas the mid-gap surface state density of both {100} surface and {111}B were reported to be high (e.g., for {100} it can reach 5 × 10 11 cm −2 ) (Offsey et al, 1986;Miller and Richmond, 1997) {112} can be considered to be comprised of {111} and {001} at a ratio of 2:1 (Joyce et al, 2010). For a free surface, this drastic difference is typically overwhelmed by the surface states introduced by oxygen (Spicer et al, 1977).…”

“…For example, the {110} surface is free of intrinsic mid-gap surface states (Spicer et al, 1977) whereas the mid-gap surface state density of both {100} surface and {111}B were reported to be high (e.g., for {100} it can reach 5 × 10 11 cm −2 ) (Offsey et al, 1986;Miller and Richmond, 1997) {112} can be considered to be comprised of {111} and {001} at a ratio of 2:1 (Joyce et al, 2010). For a free surface, this drastic difference is typically overwhelmed by the surface states introduced by oxygen (Spicer et al, 1977). Indeed, studies on bare GaAs nanowires showed near-identical surface recombination at uncapped {110} and {112} surfaces (Joyce et al, 2014).…”