Abstract
We have optimized the base electrode for InGaAs/InP based double heterojunction bipolar transistors with a buried emitter-base junction. For the buried emitter-base structure, the base metal is diffused through a thin graded quaternary region, which is doped lightly n-type, to make ohmic contact to the p+InGaAs base region. The metal diffusion depth must be controlled, or contact will also be made to the collector region. Several metal schemes were evaluated. An alloy of Pd/Pt/Au was the best choice for the base metal, since it had the lowest contact resistance and a sufficient diffusion depth after annealing. The Pd diffusion depth was easily controlled by limiting the thickness to 50Å, and using ample Pt, at least 350Å, as a barrier metal to the top layer of Au. Devices with a 500Å base region show no degradation in dc characteristics after operation at an emitter current density of 90 kA/cm2 and a collector bias, VCE, of 2V at room temperature for over 500 h. Typical common emitter current gain was 120. An ft of 95 GHz and fmax, of 131 GHz were achieved for 2×4 µm2 emitter size devices.
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Kopf, R.F., Hamm, R.A., Ryan, R.W. et al. Optimization of the base electrode for InGaAs/InP DHBT structures with a buried emitter-base junction. J. Electron. Mater. 27, 1244–1247 (1998). https://doi.org/10.1007/s11664-998-0077-4
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DOI: https://doi.org/10.1007/s11664-998-0077-4