High-sensitivity modulation-doped charge sensitive infrared phototransistors

Charge-sensitive infrared phototransistors (CSIPs) based on GaAs/AlGaAs double quantum well structures have emerged as promising detectors for the scattering type scanning near-field optical microscope (SNOM), owing to their exceptional sensitivity in infrared radiation detection. These devices enable real-space mapping of nanoscale thermal phenomena, including thermal electron energy dissipation. However, the performance of CSIP still requires further optimization to detect extremely weak near-field signals, enabling higher temporal and spatial resolution in SNOM. In this work, we have demonstrated a GaAs/AlGaAs CSIP with significantly enhanced optoelectronic performance, achieved through oxygen impurity concentration reduction and implementation of a modulation doping scheme to boost the two-dimensional electron gas mobility in the lower quantum well. The optimized device exhibits a photocurrent of 7.43μA under a source-drain bias of 30 mV at 4.2 K, achieving an exceptional responsivity of 1.34 × 10⁶A W^-1at a radiation power of 5.54 pW. Notably, the devices maintain a well-defined peak response wavelength at 11.78μm and remain operational at temperatures up to 50 K. These advancements significantly enhance the detection capability of CSIPs for near-field thermal imaging applications.