A thermodynamic investigation of indium-transition metal ohmic contacts to n-type gallium arsenide, and an overview of the thermochemical behavior of quaternary gallium-indium-(transition or noble metal)-arsenic systems

• Main Author: Swenson, Douglas James
• Format: Dissertation
• Language: English
• Subjects: chemistry, inorganic; engineering, electronics and electrical; engineering, materials science

Ohmic contacts to n-GaAs may be fabricated placing a layer of In$\sb{x}$Ga$\sb{1-x}As$ between the GaAs and the metallization layer. In order to fabricate practical ohmic contacts, one must develop a scheme by which a metallization layer containing In will react with GaAs upon annealing to form In$\sb{x}$Ga$\sb{1-x}As.$ Three mechanisms, namely, alloying, the regrowth mechanism and the exchange mechanism, have been identified by which elements such as In may be incorporated into GaAs during heat treatment. In the present study, Ni-In and PtIn$\sb2$ contacts to GaAs are fabricated, and their electrical behavior is correlated with the thermodynamics of their respective systems. These data are then used to identify the mechanism in each contact which leads to the formation of In$\sb{x}$Ga$\sb{1-x}As.$ It is found that the formation of In$\sb{x}$Ga$\sb{1-x}As$ in Ni-In contacts is due to alloying, and temperatures in excess of 800$\sp\circ$C are required for the alloying process to occur. PtIn$\sb2$ contacts, on the other hand, will not become ohmic even after having been annealed at temperatures as high as 850$\sp\circ$C. This is attributed to the very slow interdiffusion of In and Ga in In$\sb{x}$Ga$\sb{1-x}As.$ However, evidence is found to suggest that it may be possible to fabricate Pt-In-based ohmic contacts to n-GaAs via the regrowth mechanism, although this possibility requires further study. Phase equilibria are also determined experimentally in the InAs-rich regions of most In-M-As systems (where M denotes a transition or noble metal). These data, in conjunction with Ga-M-As phase equilibria reported in the literature, are then utilized to identify materials which may be utilized as thermodynamically stable contact materials to In$\rm\sb{0.53}Ga\sb{0.47}As.$