Progress in the development of a Ga(As,P) graded band gap base transistor

The graded band gap base transistor, first proposed by Kroemer, employs a change in band gap of the semiconductor within the base region of a bipolar transistor structure to produce an accelerating field for minority carriers traversing the base. This field reduces the base transit time and can increase transistor cutoff frequency. This paper describes recent results of research aimed at the examination of this device concept using the semiconductor alloy system Ga(As,P). Ga- (As,P) alloys have been synthesized by vapor phase transport-and epitaxial deposition. Deposits were formed on single crystal GaAs substrates using PCl3, AsCl3H2and GaAs as reactants. Graded band gap deposits were obtained by varying the ratio of AsCl3to PC3introduced into the epitaxial deposition reactor during deposit growth. Deposit composition and quality have been evaluated using x-ray diffraction and topography, optical reflectivity, angle lapping and staining, and Hall effect measurements.