Analytical Modeling of Current Gain in Multiple-Quantum-Well Heterojunction Bipolar Light-Emitting Transistors

We have developed an analytical model to determine the current gain of heterojunction bipolar light-emitting transistors (HBLETs) with multiple-quantum-wells (MQWs) inserted into the base of the transistor. Our modified charge-control model provides insights into the transistor's operation and facilitates the design of an efficient epi-layer structure. This can be achieved by adjusting the width of each quantum well (QW), the position of each QW in the base of heterojunction bipolar transistors (HBTs), and the separation of consecutive QWs. Our results show that the current gain decreases as the number of QWs in the base of the transistor increases, due to the "trade-off" between collector current gain and optical modulation gain. However, the current gain increases when the QW is placed near the collector. We have also investigated the number and position of QWs and their effects on charge capture, which ultimately affect the transistor's current gain. Our analytical model has been verified using previously published experimental data and layer structure designs for single and double QW-HBLETs.