Interfacial Workfunction Internal Photoemission Research Articles

High-temperature photon-type ultra-broadband detectors based on ratchet structure

Achieving a photodetector with high bandwidth, high sensitivity, high speed, and high operating temperature is a common goal for researchers, especially for infrared and terahertz regions due to its important application in various fields like military defense and biochemical analysis. Among photon-type terahertz (THz) detectors, heterojunction interfacial work function internal photoemission (HEIWIP) detectors demonstrate high bandwidth, high sensitivity, and high speed, but are limited by the low operating temperature. In this work, we developed an effective strategy for raising its operating temperature by introducing ratchet structures. By comparing with traditional HEIWIP, the ratchet HEIWIP exhibits a low dark current and high detectivity while retaining the ultra-broad response bandwidth. The operating temperature has been raised from 7 to 20 K in the terahertz region, which is meaningful progress in THz photon-type detection. The universality of this scheme makes it possible to be further migrated to general photon-type semiconductor detectors.

E-shaped patch antenna for GaAs-based broadband THz detectors

High-performance broadband terahertz (THz) photodetectors are of great interest driven by lots of applications. To improve the performance of the THz photodetector in a wide spectral coverage, the E-shaped patch antenna with three slots is proposed and studied in theory. GaAs-based homojunction interfacial work function internal photoemission (HIWIP) broadband THz detector is used as an example to demonstrate the effect in broadband detection. Due to the combined effect of the antenna and the microcavity, E-shaped patch antenna microcavity HIWIP increase the optical coupling efficiency in a broadband range from 2.1–20 THz by an average of four times. Considering the requirement to reduce the dark current, the etched E-shaped patch antenna microcavity HIWIP only retaining the active region beneath the antenna is further investigated. In contrast to the reference HIWIP, the coupling efficiency is improved by an average of 15 times in 2.3–20 THz. The high coupling efficiency of both structures leads to the significant improvement of the responsivity, noise equivalent power, and detectivity in a wide spectral coverage theoretically, which makes it possible to realize higher operating temperatures. Such a design scheme of E-shaped patch antenna structure provides a guideline for broadband THz detectors and can be used for other THz detectors.

Ultra-broadband frequency up-converter based on AlGaAs\GaAs heterojunction detector

The development of high performance is essential for the realization of ultra-broadband imaging technology, which can be widely used in astronomy, medical health, defense and security, and many other applications. In this work, we demonstrate an ultra-broadband upconversion device based on a heterojunction interfacial work function internal photoemission (HEIWIP) detector and an AlGaAs/GaAs/In0.04Ga0.96 As quantum well LED. The up-converter exhibits an ultra-broad response covering from the terahertz to mid-infrared region (3–165 THz) due to free carrier absorption and inter-valence-band absorption in p-type based photodetectors. The peak responsivity in the terahertz and mid-infrared region is measured to be 7.2 A/W at 9.2 THz and 3.5 A/W at 28.8 THz, respectively, which is improved by an order of magnitude compared to the previous homojunction interfacial work function internal photoemission-based up-converter (0.5 A/W) in the THz region. The up-converter also demonstrates an improved upconversion efficiency of 1.5%. The noise equivalent power (NEP) of the imaging system consisting of the HEIWIP-LED up-converter and Si CCD is studied. The optimized NEP can achieve ∼10 pW/Hz1/2 in both terahertz and mid-infrared regions. The HEIWIP-LED up-converter exhibits excellent properties of high responsivity, ultra-broad response, and low noise, making it a great prospect for future applications in the field of ultra-broadband imaging.

Operating temperature and the responsivity of split-off band detectors

A GaAs/AlGaAs heterojunction is used as a spin-split-off band IR detector operating at or around room temperature. This detector structure followed a similar layer architecture to the quantum well IR photo detectors (QWIP) and Heterojunction Interfacial Work function Internal Photoemission (HEIWIP) detectors. Compared to QWIPs, the emitter layer thickness is increased to avoid confinement. Unlike either the QWIPs or HEIWIPs, these detectors will have two energy gaps (barriers) to obtain the wavelength threshold which could be used to design detectors either for optimum operating temperature or optimum responsivity. The free carrier energy gap is determined by the Al fraction and the spin-split-off transition energy provides another handle on controlling the effective threshold of the detector. Unlike QWIPs, these will also detect normal incidence radiation. A preliminary detector showed a peak responsivity of 0.29 mA/W at 2.5 μm at room temperature.

GaSb homojunctions for far-infrared (terahertz) detection

A GaSb based homojunction interfacial work function internal photoemission far-infrared (>30μm) detector is presented. Metal-organic vapor phase epitaxy grown p-GaSb∕GaSb samples show 9.7A∕W peak responsivity and a peak detectivity of 5.7×1011 Jones with effective quantum efficiency of 33% at 36μm and 4.9K. The detector exhibits a 97μm (∼3THz) free carrier response threshold wavelength. Results indicate that p-GaSb homojunction internal work function internal photoemission detectors are promising candidates to be a competitor for terahertz applications.

Si doped GaAs/AlGaAs terahertz detector and phonon effect on the responsivity

Terahertz detection capability of an n-type heterojunction interfacial work function internal photoemission (HEIWIP) detector is demonstrated. Threshold frequency, f0, of 3.2THz (93μm) was obtained by using n-type GaAs emitter doped to 1×1018cm−3 and Al0.04Ga0.96As single barrier structure. The detector shows a broad spectral response from 30 to 3.2THz (10–93μm) with peak responsivity of 6.5A/W at 7.1THz under a forward bias field of 0.7kV/cm at 6K. The peak quantum efficiency and peak detectivity are ∼19% and ∼5.5×108Jones, respectively under a bias field of 0.7kV/cm at 6K. In addition, the detector can be operated up to 25K.

Ga N ∕ Al Ga N heterojunction infrared detector responding in 8–14 and 20–70μm ranges

A GaN∕AlGaN heterojunction interfacial work function internal photoemission infrared detector responding in 8–14 and 20–70μm ranges has been demonstrated. Free carrier absorption based photoresponse shows a wavelength threshold of 14μm with a peak responsivity of 0.6mA∕W at 80K under −0.5V bias. A sharp peak in the 11–13.6μm range is observed superimposed on the free carrier response. In addition, the work demonstrates 54μm (5.5THz) operation of the detector based on 1s–2p± transition of Si donors in GaN. Possible approaches on improving the performance of the detector are also addressed.

High operating temperature split-off band infrared detectors

Heterojunction interfacial work function internal photoemission detectors were used to demonstrate infrared response originating from hole transitions between light/heavy hole bands and the split-off (spin-orbit) band. A GaAs∕AlGaAs heterojunction with a threshold wavelength of ∼20μm indicated an operating temperature of 130K for split-off response in the range of 1.5–5μm with a peak D* of 1.0×108 Jones. Analysis suggests that practical devices with optimized parameters are capable of achieving room temperature operation with higher specific detectivity. Possible approaches to tailor the threshold for the split-off response to different wavelength ranges using different materials such as phosphides and nitrides are also discussed.

AlGaAs emitter∕GaAs barrier terahertz detector with a 2.3 THz threshold

A heterojunction interfacial work function internal photoemission (HEIWIP) detector with a threshold frequency (f0) of 2.3 THz (λ0=128μm) is demonstrated. The threshold limit of ∼3.3THz (92 μm) due to the Al fraction being limited to ∼0.005, in order to avoid control and transition from alloy to isoelectronic doping behavior, was surpassed using AlGaAs emitters and GaAs barriers. The peak values of responsivity, quantum efficiency, and the specific detectivity at 9.6 THz and 4.8 K for a bias field of 2.0kV∕cm are 7.3A∕W, 29%, 5.3×1011 Jones, respectively. The background-limited infrared photodetector temperature of 20 K with a 60° field of view was observed for a bias field of 0.15kV∕cm. The f0 could be further reduced toward ∼1THz regime (∼300μm) by adjusting the Al fraction to offset the effect of residual doping, and/or lowering the residual doping in the barrier, effectively lowering the band bending.

Free carrier absorption in Be-doped epitaxial AlGaAs thin films

Free hole absorption in doped AlxGa1−xAs films, grown by molecular-beam epitaxy on semi-insulating GaAs substrates, was investigated. Free carrier absorption for three different hole concentrations with the same Al fraction and for two different Al fractions with the same doping concentration was studied. Experimental absorption coefficients were obtained from the data using a model that includes multiple reflections in the substrate wafer. In the 100–400μm range, (3,5,8)×1018cm−3 Be-doped Al0.01Ga0.99As films have absorption coefficients of ∼(3,3.5,5)×103cm−1, respectively, where the magnitude of the absorption is found to be almost independent of the wavelength. This allows replacing doped GaAs emitters in heterojunction interfacial work function internal photoemission far-infrared (HEIWIP) detectors with p-AlxGa1−xAs layers with x<0.017 facilitating the extension of the threshold wavelength of HEIWIP detectors beyond the 92μm limit due to the practical Al fraction growth limit of 0.005 in molecular-beam epitaxy.

High performance single emitter homojunction interfacial work function far infrared detectors

Results are reported on p-GaAs homojunction interfacial work function internal photoemission far infrared (HIWIP FIR) detectors with a ∼1019 cm−3 carbon doped single emitter and a barrier layer for three different barrier thicknesses. A remarkably high quantum efficiency with low dark current and an increased responsivity were observed for devices with 1-, 0.1-, and 4-μm-thick barrier regions. The dark current densities for these structures are on the order of 1–10 μA/cm2 at 4.2 K, corresponding to a high dynamic resistance compared with previous HIWIP FIR detectors. A detector with a barrier thickness of 1 μm had a peak responsivity of 18.6 A/W, a peak detectivity D*=9×1011 cmHz/W, and a quantum efficiency of 40% at a wavelength of 58 μm under a reverse bias measured at 4.2 K. Cutoff wavelengths of these detectors vary with bias and are around 70 μm as expected. The main features of the absorption and responsivity spectra are well described based on a model incorporating free carrier absorption, hot hole transport, and emission over the barrier.

Resonant cavity enhancement in heterojunction GaAs/AlGaAs terahertz detectors

The room-temperature absorption and reflection spectra in the range of 5–100 μm (3–60 THz) for multilayer heterojunction interfacial work function internal photoemission (HEIWIP) GaAs/AlGaAs far-infrared (FIR) detectors are presented. Calculated results based on the free carrier absorption and interaction with optical phonons are found to be in good agreement with the experimental results. Experimental responsivity spectra demonstrate the expected maxima from the absorption measurements due to resonant cavity effects. It is shown that the resonance cavity architecture enhances the performance of the FIR HEIWIP detectors and further improvement is proposed through the use of n++ and p++ bottom contact layers or doped substrates.

Cutoff tailorability of heterojunction terahertz detectors

Heterojunction interfacial work function internal photoemission (HEIWIP) detectors provide an interesting approach to the development of quantum detectors for the terahertz range. In this letter, the cutoff frequency/wavelength variation of HEIWIP detectors having different Al fractions in AlGaAs/GaAs structures is experimentally verified, and a model is presented for designing the structures. A key feature of HEIWIP responsivity is the ability to cover a broad frequency range in a single detector with cutoff tailorability by adjusting the Al fraction in the barrier regions. Extending the response to lower frequencies by the use of AlGaAs emitters and GaAs barriers is also discussed.

Effect of interface states on the performance of GaAs p+-i far-infrared detectors

Interface states have been shown to have an appreciable effect on the performance of p-GaAs multilayer (p+-i-p+-i-…) homojunction interfacial work function internal photoemission (HIWIP) far-infrared detectors. In this article, a comparison of detector performance was made of p-GaAs HIWIP detectors with different interface state densities, with the emphasis on the detector’s dark current, noise, and capacitance characteristics.

Dark current analysis of Si homojunction interfacial work function internal photoemission far-infrared detectors

A detailed theoretical investigation of dark current mechanisms is performed for a novel Si n+-i homojunction interfacial work function internal photoemission (HIWIP) far-infrared (FIR) detector. Thermionic emission, thermionic field emission and field emission currents, including the image force effect, are calculated and compared as functions of bias voltage and temperature. The bias and temperature dependence of detector noise equivalent power (NEP), limited by thermal noise and background noise, is also calculated. From these results, the optimal operating temperatures and bias voltages are determined. Results show that Si HIWIP FIR detectors may have a performance comparable to the conventional Ge FIR detectors, with some unique advantages over them.