Development of Gallium Arsenide-Phosphide Graded Band-GAP Base Transistor Structures

摘要

The developments leading to fabrication of graded band-gap base transistor structures in gallium arsenide-phosphide are described. The material for the transistors was produced by epitaxial vapor phase deposition on GaAs substrates, using an open-tube flow system, with PCl3 and AsCl3 vapors carried over GaAs feed in a hydrogen stream. The desired composition grading for the base region was obtained by continuously varying the AsCl3-to-PCl3 ratio of the entering gases. Deposit compositions were determined by x-ray diffraction and optical reflectivity techniques, combining the latter with incremental etching to evaluate graded deposits. The transistors (n-p-n) were made by diffusing magnesium to form the base region and either alloying Au-Ge-S or diffusing sulfur through an SiO2 film to form the emitter. The best results were obtained with the diffused emitter. Good p-n junction diodes were also made using epitaxially Zn-doped Ga(As,P). Theoretical performance calculations for both n-p-n and p-n-p graded band gap base transistor showed that the optimum configuration for high-frequency performance is n-p-n with the base region graded from GaAs to GaAs0.7P0.3. If higher mobilities can be obtained in the gap-rich compositions, improved performance could be obtained by extending the grading beyond GaAs0.7P0.3. (Author)