Interfacial atomic composition and Schottky barrier heights at the Al/GaAs(001) interface

Abstract

The influence of different interfacial chemical compositions on the Schottky barrier heights across the Al/GaAs(001) interface is studied using first-principles local density functional calculations. The barrier heights are calculated for seven different interfacial chemical compositions, including the chemically abrupt As-terminated and Ga-terminated interfaces, and also several other interfaces related by Al↔Ga place exchange or containing As antisites. We find p-type barrier heights φp that vary by 0.4 eV, demonstrating a significant influence of the interface composition on the resulting barrier heights. The barrier height variation is explained by the different chemical bonding at the interface in the various cases. The metal induced gap states (MIGS) of two structures with different barrier heights are compared in order to demonstrate why such states do not result in barrier heights independent of interfacial chemical composition. It is thus suggested that the reason an experimental value of φp=0.65 eV is generally found for Al/GaAs is not due to several possible interfacial structures all having their Fermi level pinned by MIGS at the same value, but rather due to the thermodynamic preference for certain structures over others with significantly different barriers. This proposal offers a potential explanation for recent photoemission experiments that find the Fermi level position in the gap varying by several tenths of a volt as a function of the initial surface structure of the GaAs substrate: some of the samples are likely to have interfacial compositions which are metastable with respect to structures that give the standard barrier heights.

The physics and chemistry of the Schottky barrier height

“…[88][89][90] Possible interface structures and electronic structures of the Al/GaAs system have been theoretically investigated. 39,91,92 Needs et al found the SBH at epitaxial Al/GaAs(110) interface to vary by as much as 0.7 eV with a change in the interface structure. 91 A much smaller variation, $0.1 eV, was found by Bardi et al who noticed the importance of interface relaxation.…”

“…In addition, some of the most basic assumptions of the MIGS models, such as the assumption on the independence of the MIGS distribution on the metal and the assumption that the CNL is an innate property of the semiconductor, are in disagreement with the result of ab initio calculations. 4,39 It thus seems that the MIGS models have little connection with processes at real MS interfaces. Notwithstanding these known problems, pinning by MIGS has become, by far, the most frequently invoked model when SBH data are discussed in the literature.…”

Schottky barrier heights at polar metal/semiconductor interfaces

“…2 In particular, there have been reports on considerable changes in metal/Si and metal/GaAs SBH's obtained by altering the structural properties and/or the chemical composition of the interface. 8,22 The conclusion that the SBH does depend most generally on the microscopic atomic structure of the interface has been reached by many authors, both on experimental 2,3,[5][6][7][8]11,12,22 and theoretical 11,[23][24][25][26][27][28] grounds. While opening a promising line of research on Schottky barrier engineering, these observations complicate seriously the search for simple models of Schottky barrier formation, since the inclusion of the interface atomic structure seems unavoidable.…”

Effects of interface morphology on Schottky-barrier heights: A case study on Al/GaAs(001)

“…In this sense, ab initio calculations are complementary to the experimental investigations and, in the specific case of metal-semiconductor contacts, they have in fact provided in recent year a great deal of quantititave information that any successful model will have to account for. [2][3][4][5][6][7][8] Because of this theoretical work, the following facts are now well established: the barrier height does depend of the nature of the metal; [2] it does depend on the crystallographic direction; and furthermore for a given crystallographic direction of growth it even depends on the microscopic morphology of the interface.…”

“…In this sense, ab initio calculations are complementary to the experimental investigations and, in the specific case of metal-semiconductor contacts, they have in fact provided in recent year a great deal of quantititave information that any successful model will have to account for. [2][3][4][5][6][7][8] Because of this theoretical work, the following facts are now well established: the barrier height does depend of the nature of the metal; [2] it does depend on the crystallographic direction; and furthermore for a given crystallographic direction of growth it even depends on the microscopic morphology of the interface.[5] The electronic mechanisms governing the value of the Schottky barrier-as well as their variations as a function of the microscopic morphology of the interface-have not been systematically investigated so far and are basically unknown. Here we provide a contribution in this direction, by studying the barrier-height variations induced in Al/GaAs(001) by several structural and morphological perturbations which are switched on and off in our computational framework.…”