EXTRINSIC BASE SURFACE PASSIVATION IN GAINP/GAAS HETEROJUNCTION BIPOLAR-TRANSISTORS

We demonstrate excellent passivation of the extrinsic base surfaces in GaInP / GaAs heterojunction bipolar transistors (HBT's) having small emitter areas. Passivated devices with an area as small as 4 x 20 mum2 exhibit the highest reported current gain value of 2690 for GaInP / GaAs HBT's, while unpassivated 4 x 20-mum2 devices exhibit a drastically lower current gain of 500. Measured current gains as a function of collector current density are almost identical for devices with varying emitter widths of 4, 6, 8, 12, 16, and 100 mum. The current gains are also nearly identical for devices with varying passivation ledge widths of 1, 2, 3, and 6 mum. This investigation will be contrasted with a published study reporting surface passivation for a GaInP / GaAs HBT with a large emitter area.