Extrinsic base surface passivation in GaInP/GaAs heterojunction bipolar transistors

The authors demonstrate excellent passivation of the extrinsic base surfaces in GaInP/GaAs heterojunction bipolar transistors (HBTs) having small emitter areas. Passivated devices with an area as small as 4*20 mu m/sup 2/ exhibit the highest reported current gain value of 2690 for GaInP/GaAs HBTs, while unpassivated 4*20- mu m/sup 2/ devices exhibit a current gain of only 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 mu m. The current gains are also nearly identical for devices with varying passivation ledge widths of 1, 2, 3, and 6 mu m. These results are contrasted with those of a previously published study reporting surface passivation for a GaInP/GaAs HBT with a large emitter area.< >