A comparison of GaInP/GaAs HBTs with and without a base epitaxial regrowth is undertaken via static and low-frequency noise measurements. Current gain values and behaviour versus emitter area are different in both types of transistor. From low-frequency noise measurements emitter series resistances are extracted. Values of resistances are much smaller by about a factor of ten on samples without regrowth. The 1/f and g-r noise components are then analysed versus bias and geometry. For samples without regrowth, the 1/f and the g-r noise sources are mostly located at the extrinsic base surface and are due to recombinations. These recombinations are suppressed on samples with a base regrowth. On these devices, the 1/f noise sources related both to intrinsic and extrinsic phenomena are present. The g-r noise sources are located within the intrinsic transistor and more particularly in the base-collector space-charge region. This is partly explained by a thermal treatment induced by the process technology. Finally, it is shown that the base epitaxial regrowth brings a correlation between base and collector currents.
In this paper, we have studied the 1/f low frequency noise of self-aligned and non self-aligned InP/InGaAs heterojunction bipolar transistors (HBTs). The total noise of transistor is modeled by two current noise sources. The evolution with geometry, technological process and bias, of the current spectral densities referred to the input and output of the devices, permit us to locate the noise sources. Noise is mainly generated in the intrinsic transistor, and an extra noise perimetric source has been identified for the self-aligned transistors at the emitter periphery.
Low-frequency noise measurements are performed in order to characterize quasi-self-aligned polysilicon bipolar transistors. After a theoretical analysis we present a study of the influence of the base source resistance on the correlation between the input and the output noise sources of the transistors. We observe that a partial correlation between the input and the output voltage noise sources appears and varies with the source resistance, the bias and the emitter size of the transistors. As a consequence we demonstrate the influence of the fluctuations of the collector current. Taking into account these results, we propose different extraction methods for the emitter and base series resistances. To confirm and extend these measurements, high-frequency results are also presented.
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