Integrated PbTe Quantum Dots for Two-Color Detection in II–VI Wide-Bandgap Diodes

Quantum dots (QDots) composed of the narrow-bandgap semiconductor PbTe were incorporated into the depletion region of p–n junctions based on wide-bandgap II–VI semiconductors (p-ZnTe/n-CdTe). The heterostructures were grown by molecular beam epitaxy (MBE) on semi-insulating GaAs (100) substrates. The depletion region was engineered by depositing 20 alternating thin layers of CdTe and PbTe, followed by thermal annealing under ultrahigh vacuum conditions. As revealed by cross-sectional scanning electron microscopy (SEM), the initially continuous PbTe layers transformed into arrays of zero-dimensional nanostructures—PbTe quantum dots (QDs). The formation of PbTe QDs in a CdTe matrix arises from the structural mismatch between the zinc blende and rock salt crystal structures of the two materials. Electron-beam-induced current (EBIC) measurements confirmed that the PbTe QDs are located within the depletion region between the p-ZnTe and n-CdTe layers. The resulting p-ZnTe/n-CdTe diodes containing PbTe QDs exhibit pronounced sensitivity to infrared radiation in the spectral range of 1–4.5 μm, with a peak responsivity of approximately 8 V/W at a wavelength of ~2.0 μm and a temperature of 200 K. The temperature dependence of the cutoff wavelength demonstrates that the infrared response originates from band-to-band optical transitions within the PbTe QDs. In addition, the devices show sensitivity to visible radiation, with a maximum responsivity of 20 V/W at 0.69 μm. These results demonstrate that wide-bandgap p–n junctions incorporating narrow-bandgap quantum dots can function as dual-wavelength (visible and infrared) photodetectors, with potential applications in two-color detection and infrared solar cells.