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In this study, the operation of npn-type GaN-based heterojunction bipolar transistors with different net acceptor concentrations in p-base regions was simulated. It was confirmed that there is a critical net acceptor concentration (NA-ND) depending on the thickness of the base region and that if the NA-ND is lower than the critical value, the collector current may anomalously increase, regardless of base current injection. This phenomenon is caused by the punch-through process via the depletion layer extending from the collector–base junction. The effect of the valence band energy offset at the emitter-base heterojunction (ΔEV) on the current gain (β) was also investigated, and the results showed that β peaks when ΔEV is 0.22–0.30 eV. This is determined by the balance between the hot-electron injection and thermal diffusion processes in the electron transport from the emitter to the base. [ABSTRACT FROM AUTHOR]

Herein, a simulation study on novel GaN‐based n−p−n heterojunction bipolar transistors (HBTs) with a quaternary n‐AlGaInN emitter and a thin GaInN quantum well (QW) layer inserted in its p‐GaN base is reported. The idea of the quaternary AlGaInN emitter facilitates the design and independent growth of the energy bandgaps and lattice strain. In addition, the p‐GaN base inserted with the thin GaInN QW is expected to be effective in enhancing its lateral conduction via 2D hole gases (2DHGs). The simulation results indicate that the designed GaInN QW definitely functions to generate and transport the 2DHGs and ultimately contributes to the improvement of the device performance. In other words, the lateral resistivity of the p‐GaN base is reduced from 1.8 × 10−1 to 7.0 × 10−2 Ω cm with the use of the GaInN QW insertion layer. Further, the simulation study focusing on the lateral distance between the n‐emitter and p‐base electrodes exhibits stable device characteristics for the HBT with the GaInN QW insertion layer compared with the conventional HBT structure. Dynamic analysis of the carrier concentration distribution indicates that the QW functions as a low‐resistance current path and it has the effect of avoiding the punch‐through phenomenon. [ABSTRACT FROM AUTHOR]