Pingping Chen

High-sensitivity, bias-selective dual-band infrared detection is essential for two-color absolute thermometry of mid- to long-wavelength infrared sources, including the picowatt-class signal regime relevant to cryogenic near-field thermal measurements. Here, we report a triple-quantum-well charge-sensitive infrared phototransistor in which two spatially isolated floating gates provide electrically separated photoresponse pathways, allowing the 10.1 and 16.4 μm channels to be addressed individually or jointly by gate bias. The cross-hole plasmonic grating supports two geometrically distinguishable resonances with different dominant tuning sensitivities: a period-dominated Rayleigh anomaly–surface plasmon polaritons (SPP) mode and an arm-length-dominated localized shape plasmon–SPP hybrid mode. This partially mode-decoupled response reduces spectral entanglement and enables practical co-design of the two infrared bands. At an optimized well doping of 8.0 × 1017 cm−3, the device delivers an integration responsivity of 6.17 × 105 A W−1 at VSD = 10 mV under a 4.24 pW, 300 K background; the band-resolved photocurrent responsivities at VSD = 120 mV are 1.35 × 103 A W−1 at 10.1 μm and 6.07 × 103 A W−1 at 16.4 μm. Quantum efficiencies of 19.4% (10.1 μm) and 16.0% (16.4 μm) yield specific detectivities of 8.5 × 1011 and 1.1 × 1012 cm Hz1/2 W−1, respectively, with a balanced (∼1:1) dual-band spectral response suitable for two-color pyrometry. The architecture establishes a route to high-gain dual-band mid- to long-wavelength infrared sensing for cryogenic two-color thermometry.

The self-catalyzed growth of InAs nanowires (NWs) on graphene is achievable but typically yields short, thick NWs with frequent stacking-fault defects. In this work, we demonstrate the successful synthesis of defect-free, ultralong InAs NWs by harnessing the synergistic effects of graphene and an Au catalyst. The distinct roles of graphene and Au in promoting the growth of high-quality NWs were systematically elucidated. Atomic resolution scanning transmission electron microscopy (STEM) imaging revealed that the Au-catalyzed InAs NWs grown on graphene predominantly exhibit defect-free wurtzite structures, whereas a small portion of nanosheets and the NWs grown atop them display defect-free zinc blende phases. Based on these observations, a growth model for Au-catalyzed InAs NWs on defective graphene/Ge surfaces was proposed.

High-performance multispectral infrared photodetectors are essential for advanced imaging and sensing technologies. Here, we demonstrate a frequency division multiplexed (FDM) dual-band infrared phototransistor operating at 9.9 and 14.9 μm through a single source–drain channel. The device incorporates a double GaAs/AlGaAs quantum well (QW) structure, where two QWs of different thicknesses (7 and 11 nm) serve as charge-sensitive intersubband absorbers. Optical excitation at each wavelength induces opposite charge polarities on a floating gate, which are selectively demodulated by periodic resetting with distinct frequencies. This FDM operation enables simultaneous, independent readout of both spectral bands. Finally, we demonstrate absolute temperature sensing using the dual-band response, highlighting the device's potential for compact multispectral infrared sensing and imaging systems.

HgTe quantum wells (QWs) with inverted band structures and strong spin–orbit coupling provide a versatile platform for studying topological quantum transport. Quantum Hall scaling near plateau–plateau transitions provides a sensitive probe of the crossover between localized and extended states. Here we investigate plateau–plateau transitions in a 23 nm-wide HgTe QW with a reduced effective energy gap, where macroscopic transport is not strictly limited to a single effective two-dimensional channel. By analyzing the temperature- and illumination-dependent maximum Hall slope, we extract the scaling exponent κ, which is treated here as an effective scaling exponent derived from macroscopic transport, and identify a pronounced temperature-driven crossover. At low temperatures, κ deviates from commonly reported values and evolves toward the range typically observed in conventional two-dimensional systems at elevated temperatures, while Landau-level quantization remains clearly identifiable. Infrared illumination further modifies the extracted κ and shifts the crossover toward lower temperatures, reflecting an effective modulation of the transport response. These results show that quantum Hall scaling in wide HgTe QWs is influenced by the interplay between disorder-related dissipative transport and finite phase coherence, highlighting the applicability and limitations of scaling analysis beyond the single effective two-dimensional channel regime.

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 7.43 μ A under a source-drain bias of 30 mV at 4.2 K, achieving an exceptional responsivity of 1.34 × 10 ⁶ A W ⁻¹ at a radiation power of 5.54 pW. Notably, the devices maintain a well-defined peak response wavelength at 11.78 μ m and remain operational at temperatures up to 50 K. These advancements significantly enhance the detection capability of CSIPs for near-field thermal imaging applications.

InGaAs nanowires (NWs) show exceptional potential in near-infrared photodetection due to their excellent optoelectronic properties. However, the high intrinsic carrier concentration of the InGaAs NW and the ionization scattering caused by surface defect states result in a high dark current, which degrades the photodetection performance. Here, we prepared an InGaAs NW field-effect transistor modulated by ferroelectric polymer P(VDF-TrFE), where the non-volatile ultra-high electrostatic field from polarization of the P(VDF-TrFE) film modulates the carrier distribution and energy band structure inside the NW. When the P(VDF-TrFE) film is in a negative polarization state, the electrostatic field depletes the carriers in the NW channel, remarkably suppressing the dark current by over two orders of magnitude. Consequently, our single InGaAs NW photodetector achieves both remarkable responsivity (R) of 1.1 × 103 A W−1 and specific detectivity (D*) of 7.5 × 1012 Jones at the optical communication wavelength, significantly exceeding the commercial InGaAs and the nanowire-based photodetector. Moreover, the suppressed dark current enhances the polarization-sensitive detection capability, increasing the polarization ratio from 1.3 to 3.6. This enables the application of our device to polarization-sensitive infrared imaging. Our work demonstrates the value of ferroelectric polymer modulation for low-dimensional, high-performance infrared photodetectors.

Perfect graphene substrates can improve the quality of films grown by large-mismatch heteroepitaxy and simultaneously enable the transfer of epitaxial layers. However, large-area chemical vapor deposition-grown graphene suitable for practical applications typically contains various defects, and the influence of these defects on heteroepitaxial growth remains unclear. In this work, we systematically investigated the molecular beam epitaxy growth of CdTe films on graphene/Ge substrates. The effects of graphene defects on the nucleation behavior and crystal structure of CdTe grains were elucidated, and epitaxial models for CdTe on three types of graphene/Ge surfaces were proposed. Furthermore, we evaluated the crystal quality of CdTe films grown on different graphene/Ge substrates and found that the quality of the epitaxial films is strongly correlated with the defects in graphene.

Growth on patterned graphene/Ge provides a route to improve the film quality of large mismatch heteroepitaxy and simultaneously facilitate the transfer of epitaxial films; however, the growth process and its associated technical challenges remain unclear. In this work, the molecular beam epitaxy (MBE) growth of CdTe films on micro-scale patterned strip-like graphene/Ge (100), containing selective area epitaxy (SAE) of CdTe seeds on exposed Ge and the merging process of CdTe seeds, were systematically investigated. The effects of growth temperature on the SAE of CdTe seeds were studied in detail, and a growth model of the CdTe seeds was proposed. Additionally, we examined the morphology and crystal quality of CdTe films at different growth stages, identifying the suppression of CdTe nucleation on graphene during the CdTe seed growth and merging as a key challenge to obtain high-quality films on patterned graphene/Ge.