Ultrahigh Thermal Sensitivity Using a Darlington-Cascaded Triple-Quantum-Well Heterojunction Bipolar Light-Emitting Transistors

This study introduces a novel approach to enhance the current sensing capabilities of triple quantum-well heterojunction bipolar transistors (TQW-HBTs) through a cascaded Darlington transistor pair configuration. The circuit, comprising two intricately designed TQW-HBTs, is thoroughly investigated for its temperature-dependent collector current behavior across substrate temperatures ranging from $25~^{\circ }$ C to $85~^{\circ }$ C. The Darlington configuration significantly amplifies the low sensing current of the TQW-HBT, achieving a current gain of 1.59 at $25~^{\circ }$ C and 1.83 at $85~^{\circ }$ C under a common bias of ${V}_{\text {CE}}$ of 3.6 V and ${I}_{\text {B}}$ of 1 mA. The TQW-HBT exhibits an increase in current gain from 0.37 to 0.94 as the temperature rises from $25~^{\circ }$ C to $85~^{\circ }$ C, while the Darlington transistor achieves a larger increase in current gain from 0.59 to 1.71 under the same conditions. At $25~^{\circ }$ C, the current sensitivity of the TQW-HBT is measured at $5.74~\mu $ A/°C, while the Darlington transistor demonstrates a higher sensitivity of $10.15~\mu $ A/°C. As the temperature reaches $85~^{\circ }$ C, these sensitivities further increase to $12.86~\mu $ A/°C for the TQW-HBT and $27~\mu $ A/°C for the Darlington transistor. Additionally, the circuit allows for the current-to-voltage conversion, achieving a maximum voltage sensitivity of 16.07 mV/°C at $85~^{\circ }$ C, with ${V}_{\text {DD}}$ of 4 V and ${I}_{B}$ of 1 mA. These results highlight the superior performance of the TQW-HBT cascaded Darlington transistor over conventional bipolar-based temperature sensors, positioning it as a promising candidate for the next-generation ultrahigh-sensitivity thermal sensor technologies.