The interaction of gold with gallium arsenide

Abstract

Gold and gold-based alloys, commonly used as solar-cell contact materials, are known to react readily with gallium arsenide. Experiments designed to identify the mechanisms involved in these GaAs-metal interactions have yielded several interesting results. It is shown that the reaction of GaAs with gold takes place via a dissociative diffusion process. It is shown further that the GaAs-metal reaction rate is controlled to a very great extent by the condition of the free surface of the contact metal, an interesting example of which is the previously unexplained increase in the reaction rate that has been observed for samples annealed in a vacuum environment as compared to those annealed in a gaseous ambient. A number of other hard-to-explain observations, such as the low-temperature formation of voids in the gold lattice and crystallite growth on the gold surface, are also explained by invoking this mechanism.

On the annealing mechanism of AuGe/Ni/Au ohmic contacts to a two-dimensional electron gas in GaAs/AlxGa1−xAs heterostructures

“…This concerns the formation of new material phases. In several earlier studies [9,19,12,14,[16][17][18] these phases have been identified as AuGa alloys and phases close to Ni 2 GeAs. These phases penetrate only tens of nm below the original wafer surface for typical annealing conditions [9,14].…”

“…Various authors have suggested that the increasing contact resistance that is associated with over annealing may be due to a large number of vacancies just below the metal-rich phases near the surface [19,14,24] (but others suggested it was due to excessive in-diffusion of Ni [5,14]). These mainly result from out-diffusion of Ga into the Au-rich grains (which indeed results in a very stable AuGa phase near the original wafer surface [5,16,17]). These vacancies occur in particular when there is no (longer) Ge diffusion into these vacancies.…”

“…The AuGe/Ni/Au contact was first introduced by Braslau et al [4] to contact n-GaAs, and several studies aimed at understanding the contact mechanism for this type of contact [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Later studies focused on the formation of an ohmic contact to a 2DEG in a GaAs/Al x Ga 1−x As heterostructure [19][20][21][22][23][24][25][26][27], but do not report how the optimal annealing parameters depend on the depth of the 2DEG below the surface.…”

Ballistic electron emission microscopy studies of electron scattering in Au/GaAs Schottky diodes damaged by focused ion beam implantation

“…Gallium defects in the Au are expected as Au and GaAs are thought to react 31 through a dissociative diffusion mechanism 32,33 in which Ga enters the Au as an interstitial. These Ga i atoms are very mobile 31,32 but have a very low solubility limit.…”

“…However, when a Ga i encounters a gold vacancy V Au , the vacancy is annihilated and a substitutional Ga s is formed. 32,35 Therefore, the diffusion rate is approximated as equal to D Au . As the Ga i are removed, more are allowed to enter from the GaAs.…”