SEMI M19 - Specification for Electrical Properties of Bulk Gallium Arsenide Single Crystal Substrates
For the specification, three principal types of material were identified: semi-insulating, n-type, and p-type. This encompasses the full range of conductivity characteristics for gallium arsenide (GaAs). § 3 considers subclasses of these characteristics defining the species which may be used for producing the conductivity type. For semi-insulating material, special cases have been isolated.
Undoped, Grade A1 represents those materials which are of high resistivity and stable following growth, without necessitating any additional annealing or processing. The Grade A2 material, "high purity", requires additional thermal processing following growth to bring the resistivity to a level > 107 Ω-cm. At this time, most producers have indicated that the majority of the Grade A2 ingots have resistivity characteristics which rise into the acceptable range after an appropriate thermal cycle. However, this phenomenon is sensitive to the details of the time-temperature cycle, and thus, such an increase cannot be guaranteed in every application. Thus, the label "Grade A2" is used to denote this material.
Chromium doping produces a high resistivity material. However, due to the rapid diffusion of Cr during processing and the propensity for surface accumulation, it is not as well suited to processing as grades 3.A.1 and 3.A.2, thus we assign this material "Grade A".
Iso-electric dopant additions do not appear to affect the resistivity significantly, but rather, permit the reduction of dislocation generation in the final product. Thus, this material is classified Grade A. While In is the most effective hardening agent, Al, P, and Sb are also viable species. They are included for completeness and to reduce the likelihood of document revision at a later date. The Grade B specification encompasses those materials where the impurity and point defect densities are not quite in the proper balance, but the resistivity is suitable for less-stringent applications.
For conducting material, the best characterized, non-transition metal species have been included as n-type dopants; for p-type, a broader range of species has been included, as transition metals are useful acceptor impurities.
Referenced SEMI Standards