Mid-infrared photodetectors operating over an extended wavelength range up to 90 K

We report a wavelength threshold extension, from the designed value of 3.1 to 8.9 μm, in a -type heterostructure photodetector. This is associated with the use of a graded barrier and barrier offset, and arises from hole–hole interactions in the detector absorber. Experiments show that using long-pass filters to tune the energies of incident photons gives rise to changes in the intensity of the response. This demonstrates an alternative approach to achieving tuning of the photodetector response without the need to adjust the characteristic energy that is determined by the band structure

Wavelength-extended photovoltaic infrared photodetectors

We report the incorporation of a long-wavelength photovoltaic response (up to 8μm) in a short-wavelength p-type GaAs heterojunction detector (with the activation energy of EA∼0.40 eV), operating at 80K. This wavelength-extended photovoltaic response is enabled by employing a non-symmetrical band alignment. The specific detectivity at 5μm is obtained to be 3.5×10 cm Hz/W, an improvement by a factor of 10 over the detector without the wavelength extension

Tunable hot-carrier photodetection beyond the bandgap spectral limit

The spectral response of common optoelectronic photodetectors is restricted by a cutoff wavelength limit λ that is related to the activation energy (or bandgap) of the semiconductor structure (or material) (Δ) through the relationship λ = hc/Δ. This spectral rule dominates device design and intrinsically limits the long-wavelength response of a semiconductor photodetector. Here, we report a new, long-wavelength photodetection principle based on a hot-cold hole energy transfer mechanism that overcomes this spectral limit. Hot carriers injected into a semiconductor structure interact with cold carriers and excite them to higher energy states. This enables a very long-wavelength infrared response. In our experiments, we observe a response up to 55 μm, which is tunable by varying the degree of hot-hole injection, for a GaAs/AlGaAs sample with Δ = 0.32 eV (equivalent to 3.9 μm in wavelength)

Editorial for the Special Issue on Semiconductor Infrared Devices and Applications

Infrared radiation (IR) was accidentally discovered in 1800 by the astronomer Sir William Herschel [...

Temperature-dependent internal photoemission probe for band parameters

The temperature-dependent characteristic of band offsets at the heterojunction interface was studied by an internal photoemission (IPE) method. In contrast to the traditional Fowler method independent of the temperature (T), this method takes into account carrier thermalization and carrier/dopant-induced band-renormalization and band-tailing effects, and thus measures the band-offset parameter at different temperatures. Despite intensive studies in the past few decades, the T dependence of this key band parameter is still not well understood. Re-examining a p-type doped GaAs emitter/undoped Al x Ga 1−x As barrier heterojunction system disclosed its previously ignored T dependency in the valence-band offset, with a variation up to ∼−10 −4 eV/K in order to accommodate the difference in the T -dependent band gaps between GaAs and AlGaAs. Through determining the Fermi energy level (E f ), IPE is able to distinguish the impurity (IB) and valence bands (VB) of extrinsic semiconductors. One important example is to determine E f of dilute magnetic semiconductors such as GaMnAs, and to understand whether it is in the IB or VB

STUDY OF EXTENDED WAVELENGTH INFRARED DETECTION ON P-GAAS/ALGAAS HETEROSTRUCTURES

The wavelength threshold of a semiconductor photodetector is determined by the conventional rule λ = hν/Δ, where Δ is the minimum energy gap of the material, or the interfacial energy gap of the heterostructure. In addition, the dark current and noise levels of the detector is also determined by the Δ. Therefore, there is always a trade-off between increased noise levels and longer spectral threshold due to lowering the Δ. It has been recently demonstrated that the standard limit of can be overcome in extended wavelength infrared detectors. Specifically, a detector a photodetector designed with Δ = 0.40 eV ( = 3.1 µm) showed an extended wavelength threshold up to ~68 µm, ~45 µm, and to ~60 µm, under positive, zero, and negative biases respectively, at 5.3K. p-GaAs/AlGaAs heterostructure-based infrared detectors were utilized in this study. A barrier energy offset (δE) between AlGaAs barriers, is found to be necessary for the spectral extension mechanism, where wavelength extension mechanism was not observed on a reference detector without an offset. The dark current, however, was seen to correspond to Δ = 0.40 eV, which was confirmed by a fitting obtained by using a 3D carrier drift model. Further study with a variation in δE and gradient of the AlxGa1-xAs barrier are in progress, which are expected to shed more light on the underlying mechanism of hot carrier effect

RAPID DETECTION OF CELL ACTIVATION

Rapid detection of infections or monitoring the therapeutic response during the treatments is critical to improve the expected outcome. Currently, available infection diagnostic or monitoring methods are expensive, time-consuming and require well-trained personnel. This study presents rapid and reliable Fourier Transform Infrared (FTIR) spectroscopy to elucidate the alteration in molecular interactions due to infections. As a model for the cell activation due to pathogen infection or allergies, T-cell samples with and without anti-CD3 antibody treatment was used. At the incubation time with the antibody is 75 minutes, a statistically significant alteration (p \u3c 0.02, using paired t-test with post-hoc Bonferroni corrections) in infrared absorbance values of spectral positions at 1367 and 1358 cm-1, was observed. This technique could be useful for precise evaluation of various infectious diseases or allergies and their therapeutic modalities