On the Emitter Resistance of High-Performance GaAs- and InP-Based Heterojunction Bipolar Transistors

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Emitter resistance $R_{\text{EE}}$ and collector current ideality factor $n_{\text{C}}$ of InGaP/GaAs heterostructure bipolar transistors (HBTs) and InP/InGaAs double-HBTs (DHBTs) were investigated from the viewpoints of DC and RF characteristics. It was found that the apparent ideality factor of collector current $n_{\text{C}}^{\text{app}}$ increases with the collector current $I_{\text{C}}$ for all HBTs. The increase in $n_{\text{C}}^{\text{app}}$ is more conspicuous in the InP/InGaAs DHBTs than in the InGaP/GaAs HBTs. The most likely explanation is that the $R_{\text{EE}}$ consists of two components: one is the well-known contact resistivity $R_{\text{EE}}^{0}$ and the other is band-profile-dependent resistivity $R_{\text{Ei}}$, which decreases as $I_{\text{C}}$ increases. In the InP/InGaAs DHBTs, the increase in $n_{\text{C}}^{\text{app}}$ with $I_{\text{C}}$ is made remarkable by the insertion of an InGaAs etching stop layer (ESL) that makes it easy to form a ledge structure indispensable for high-reliability and high-performance HBTs. However, with the increase of $I_{\text{C}}$, the difference in $R_{\text{EE}}$ between the InP/InGaAs DHBTs with and without the ESL becomes small. The insertion of an ESL is considered acceptable for high-speed IC applications. Using an emitter structure with an ESL, we developed self-aligned InP/InGaAs DHBTs with a ledge passivation structure that attained an $ f_{\text{T}}$ of 302 GHz, $ f_{\text{max}}$ of 388 GHz, and $\mathit{BV}_{\text{CEO}}$ of 6.2 V.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2008-06-25

On the Emitter Resistance of High-Performance GaAs- and InP-Based Heterojunction Bipolar Transistors

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