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 wer e analyzed. Comparisons of the experimental results of these HBT's est ablish that the dominant carrier transport mechanism in GaInP/GaAs HBT 's is the carrier diffusion through the base layer. This finding sugge sts that the conduction-band barrier across the GaInP/GaAs emitter-bas e junction is so small that the barrier spike does not affect the carr ier transport. This finding differs from other published works which, through studying device structures other than HBT's, determined the co nduction band barrier to be as large as approximately 50% of the bandg ap difference. The findings of the present investigation, however, agr ee well with another published work which also examined an HBT structu re. The difference between these works is discussed.