Properties of Al, (AuGe)-GaAs contacts fabricated by combining ion-beam treatment and metallization

Abstract

because many questions connected with the modification of the structure and chemical composition of a GaAs surface still have not been investigated. The characteristic features of the formation of contacts with both barrier ~Al! and Ohmic ~AuGe! metallizations integrating the aluminum or AuGe euctectic deposition processes with preliminary IBT were investigated using a combination of electrophysical, optical, and secondary-emission methods. The chemical composition of a AuGe‐GaAs heterostructure was analyzed using layer-by-layer ion etching, while the characteristic features of the interphase interactions in Al‐GaAs contacts were studied during formation of the contacts starting with submonolayer coatings. Figure 1 displays the distribution of the atomic components in a AuGe‐GaAs contact before ~a! and after ~b! IBT of a GaAs surface with Ar 1 ions (E5200 eV). One can see that the destruction which occurs in the near-surface region of GaAs during bombardment and is accompanied by the generation of defects in the semiconductor lattice stimulates Ge diffusion in the GaAs surface layer. This is also promoted by the active absorption of Ga by the Au film, observed in these structures under these conditions. At the same time, the changes in the As profiles are smaller, and considering the poor solubility of As in Au and the absence of intermetallic compounds of gold with arsenic, the observed blurring of the As profile is most likely due to the morphology of the film coating. The changes noted in the microstructure and atomic composition of the interphase boundary ~IPB! of the contact lead to a change in its electric characteristics ~see Table I!. The observed decrease in the contact resistance R under optimal ion bombardment conditions is a consequence of Ge diffusion in the surface region of GaAs. Although a quite high potential barrier ~0.5 eV! is formed at the AuGe‐GaAs interface, the increase in the donor impurity concentration ~Ge! in the surface layer of GaAs results in a narrower barrier for current flow in the contact and a larger tunneling component of the current. The weak effect of the ion beam on R under other bombardment conditions and even its increase are apparently due to compensation effects due to Au diffusion in GaAs or the formation of an amorphized layer, whose contribution to the contact resistance is determined by its thickness and conductivity. The ion-bombardment-stimulated changes in the parameters of surface-barrier structures ~see Table I! are accompanied by a more complicated interphase interaction mechanism, primarily due to the greater role of chemical effects. In this case, the dominant processes are Al reduction processes in the oxide phases of the GaAs surface and the formation of intermetallic phases with the semiconductor components. 3 This results in a more homogeneous phase, which replaces the initial heterogeneous oxide layer on the GaAs surface. In the process, Ga diffuses to the surface of the metal film, and this changes the defect composition of the near-surface layer of the semiconductor. An investigation of the photoluminescence ~PL! spectra confirmed the radical changes produced in the defect composition of the semiconductor layer in contact with the metal by these processes. It was found that the generated defects influence the magnitude of the Schottky barrier, but they play a larger role in the processes associated with current flow. As their density increases, the Schottky barrier undergoes degradation.