CURRENT TRANSPORT MECHANISM IN GAINP/GAAS HETEROJUNCTION BIPOLAR-TRANSISTORS

GaInP/GaAs heterojunction bipolar transistors (HBT's) and both graded and abrupt AlGaAs/GaAs HBT's were fabricated. A total of 20 wafers were analyzed. Comparisons of the experimental results of these HBT's establish that the dominant carrier transport mechanism in GaInP/GaAs HBT's is the carrier diffusion through the base layer. This finding suggests that the conduction-band barrier across the GaInP/GaAs emitter-base junction is so small that the barrier spike does not affect the carrier transport. This finding differs from other published works which, through studying device structures other than HBT's, determined the conduction band barrier to be as large as approximately 50% of the bandgap difference. The findings of the present investigation, however, agree well with another published work which also examined an HBT structure. The difference between these works is discussed.