Abstract

This paper presents a comparative study, based on DC, RF and low frequency noise (LFN) measurements, between Carbon-doped, and Indium/Carbon doped GalnP/GaAs HBT's featuring different emitter widths. Both technologies exhibit an evident emitter size ef­fect, while C-doped devices have larger DC and RF gains and a lower input voltage noise level. The bet­ter performance has been justified in terms of a higher quality of the extrinsic base surface. This explanation was supported by the LFN measurements carried out on self-aligned devices, which revealed an electron dif­fusion current from the emitter toward the base, proba­bly due to the pinning of the Fermi level at the surface. The HBT's have been compared also in terms of relia­bility by means of electrical stress performed at room temperature. The effect, of the stress Was a DC cur­rent gain increase associated with a reduction of the base current and of the input voltage noise lorentzian component. The In/C doped devices exhibited the largest variations, and were more sensitive to the cur­rent stress.