Modelamento de transistores bipolares de heterojunção

AUTOR(ES)
DATA DE PUBLICAÇÃO

1995

RESUMO

A study about current transport mechanism through a heterojunction is presented. Drift and diffusion mechanism are not enough to describe the electrical current (due to a spike in the conduction band of the Npn transistor). This has led to the introduction of the Thermionic-Emission mechanism. The Ebers-Moll and Gummel-Poon models are also compatible with this last mechanism. The equations of the base and collector currents for a transistor with a single heterojunction are developed, considering that parasitic resistances and thermal effects are negligible. It is shown that both models, Ebers-Moll and Gummel-Poon, are equivalent. Based on this, the Ebers-Moll model was selected. By comparing the calculated currents with the experimental ones, it is I shown that the calculated ones are much smaller. This is proposed to be I attributed to the tunneling through the spike. The effect of tunneling is to increase the parameters of saturation current (IS) and ideality factor (nF). A good , fit between experiment and model is obtained by this way. For high base-emitter bias values, however, the model deviates from the experimental curve. A set of DC measurement techniques was implemented and parameter extraction procedures were implemented and analyzed. A small signal model was derived from the DC model and a methodology for extracting the parameters of the model from the S parameters of the devices is presented. The actual extraction of the AC parameters of the devices was not possible due to high parasitic effects associated to the layout of the pads. Corrections for the problem are presented. Three different types of devices were measured and compared: homojunction bipolar transistors, HBTs of AIGaAs/GaAs and HBTs of InP/lnGaAs. For the AIGaAs/GaAs devices, no bias range with constant relation between base and collector currents was obtained, due to a high lateral recombination current. On the other hand, for the InP/lnGaAs devices, a constant relation between base and collector current was obtained, in this case attributed to a high recombination current in the neutral base region

ASSUNTO(S)

transistores de junção transistores bipolares

ACESSO AO ARTIGO

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