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1. High broadband photoconductivity of few-layered MoS 2 field-effect transistors measured using multi-terminal methods: effects of contact resistance

   https://doi.org/10.1039/D0NR07311C  

   Das, Priyanka ; Nash, Jawnaye ; Webb, Micah ; Burns, Raelyn ; Mapara, Varun N. ; Ghimire, Govinda ; Rosenmann, Daniel ; Divan, Ralu ; Karaiskaj, Denis ; McGill, Stephen A. ; et al ( January 2020 , Nanoscale)

   null (Ed.)

   Among the layered two dimensional semiconductors, molybdenum disulfide (MoS 2 ) is considered to be an excellent candidate for applications in optoelectronics and integrated circuits due to its layer-dependent tunable bandgap in the visible region, high ON/OFF current ratio in field-effect transistors (FET) and strong light–matter interaction properties. In this study, using multi-terminal measurements, we report high broadband photocurrent response ( R ) and external quantum efficiency (EQE) of few-atomic layered MoS 2 phototransistors fabricated on a SiO 2 dielectric substrate and encapsulated with a thin transparent polymer film of Cytop. The photocurrent response was measured using a white light source as well as a monochromatic light of wavelength λ = 400 nm–900 nm. We measured responsivity using a 2-terminal configuration as high as R = 1 × 10 3 A W −1 under white light illumination with an optical power P opt = 0.02 nW. The R value increased to 3.5 × 10 3 A W −1 when measured using a 4-terminal configuration. Using monochromatic light on the same device, the measured values of R were 10 3 and 6 × 10 3 A W −1 under illumination of λ = 400 nm when measured using 2- and 4-terminal methods, respectively. The highest EQE values obtained using λ = 400 nm were 10 5 % and 10 6 % measured using 2- and 4-terminal configurations, respectively. The wavelength dependent responsivity decreased from 400 nm to the near-IR region at 900 nm. The observed photoresponse, photocurrent–dark current ratio (PDCR), detectivity as a function of applied gate voltage, optical power, contact resistances and wavelength were measured and are discussed in detail. The observed responsivity is also thoroughly studied as a function of contact resistance of the device. 

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2. Dark energy survey year 3 results: cosmology from galaxy clustering and galaxy–galaxy lensing in harmonic space

   https://doi.org/10.1093/mnras/stae2654  

   Faga, L. ; Andrade-Oliveira, F. ; Camacho, H. ; Rosenfeld, R. ; Lima, M. ; Doux, C. ; Fang, X. ; Prat, J. ; Porredon, A. ; Aguena, M. ; et al ( November 2024 , Monthly Notices of the Royal Astronomical Society)

   We present the joint tomographic analysis of galaxy-galaxy lensing and galaxy clustering in harmonic space (HS), using galaxy catalogues from the first three years of observations by the Dark Energy Survey (DES Y3). We utilize the redMaGiC and MagLim catalogues as lens galaxies and the metacalibration catalogue as source galaxies. The measurements of angular power spectra are performed using the pseudo-$C_\ell$ method, and our theoretical modelling follows the fiducial analyses performed by DES Y3 in configuration space, accounting for galaxy bias, intrinsic alignments, magnification bias, shear magnification bias and photometric redshift uncertainties. We explore different approaches for scale cuts based on non-linear galaxy bias and baryonic effects contamination. Our fiducial covariance matrix is computed analytically, accounting for mask geometry in the Gaussian term, and including non-Gaussian contributions and super-sample covariance terms. To validate our HS pipelines and covariance matrix, we used a suite of 1800 log-normal simulations. We also perform a series of stress tests to gauge the robustness of our HS analysis. In the $\Lambda$CDM model, the clustering amplitude $S_8 =\sigma _8(\Omega _m/0.3)^{0.5}$ is constrained to $S_8 = 0.704\pm 0.029$ and $S_8 = 0.753\pm 0.024$ (68 per cent C.L.) for the redMaGiC and MagLim catalogues, respectively. For the wCDM, the dark energy equation of state is constrained to $w = -1.28 \pm 0.29$ and $w = -1.26^{+0.34}_{-0.27}$, for redMaGiC and MagLim catalogues, respectively. These results are compatible with the corresponding DES Y3 results in configuration space and pave the way for HS analyses using the DES Y6 data.

    

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3. Photogating-driven enhanced responsivity in few-layered ReSe2 phototransistor

   https://doi.org/10.1039/D1TC01973B  

   Patil, Prasanna Dnyaneshwar ; Wasala, Milinda ; Alkhaldi, Rana ; Weber, Lincoln ; Kovi, Kiran Kumar ; Chakrabarti, Bhaswar ; Nash, Jawnaye ; Rhodes, Daniel ; Rosenmann, Daniel ; Divan, Ralu ; et al ( January 2021 , Journal of Materials Chemistry C)

   null (Ed.)

   A wide variety of two-dimensional (2D) metal dichalcogenide compounds have recently attracted much research interest due to their very high photoresponsivities (R) making them excellent candidates for optoelectronic applications. High R in 2D photoconductors is associated to trap state dynamics leading to a photogating effect, which is often manifested by a fractional power dependence (γ) of the photocurrent (I ph ) when under an effective illumination intensity (P eff ). Here we present photoconductivity studies as a function of gate voltages, over a wide temperature range (20 K to 300 K) of field-effect transistors fabricated using thin layers of mechanically exfoliated rhenium diselenide (ReSe 2 ). We obtain very high responsivities R ~ 16500 A/W and external quantum efficiency (EQE) ~ 3.2 x 10 6 % (at 140 K, V g = 60 V and P eff = 0.2 nW). A strong correlation between R and γ was established by investigating the dependence of these two quantities at various gate voltages and over a wide range of temperature. Such correlations indicate the importance of trap state mediated photogating and its role in promoting high photo responsivities in these materials. We believe such correlations can offer valuable insights for the design and development of high performance photoactive devices using 2D materials. 

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4. Photocurrent Generation Mechanisms in Molybdenum‐Contacted Semiconducting Black Phosphorus and Contributions from the Photobolometric Effect

   https://doi.org/10.1002/pssa.202100196  

   Saenz, Gustavo A. ; Mehta, Ravindra K. ; Fadil, Dalal ; Kaul, Anupama B. ( August 2021 , physica status solidi (a))

   An analysis of the optoelectronic properties and photocurrent generation mechanisms in 2D multilayer crystallites of black phosphorus (BP) is conducted from 350 K down to cryogenic temperaturesTof ≈6 K using a broad‐band white light source, and the results are compared to another semiconducting van der Waals solid, MoS₂. Both the BP and MoS₂devices are contacted with Mo at the bottom as the electrode metal. The Mo–BP interface yields a low Schottky barrier ≈ −28.3 meV and a high photoresponsivityRof ≈2.43 × 10⁵ A W⁻¹at a source‐drain bias voltage of ≈0.5 V (300 K, and incident optical power ≈3.16 μW cm⁻²). This article is the first to highlight the empirical use of Mo as a contact metal with BP. The highRis attributed to the low at the interfaces, in conjunction with the large effective area of a bottom contact architecture that increases the collection of photoexcited carriers and reduces thermal dissipation into the substrate from the largely suspended 2D nanodiaphragm. The results show the promise of BP to potentially advance thermoelectric and optoelectronic devices stemming from this monoelemental, direct bandgap 2D van der Waals solid.

    

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5. Self-heating in ultra-wide bandgap n-type SrSnO3 thin films

   https://doi.org/10.1063/5.0105962  

   Golani, Prafful ; Saha, Chinmoy Nath ; Sundaram, Prakash P. ; Liu, Fengdeng ; Truttmann, Tristan K. ; Chaganti, V. R. Saran Kumar ; Jalan, Bharat ; Singisetti, Uttam ; Koester, Steven J. ( October 2022 , Applied Physics Letters)

   This work reports the quantification of rise in channel temperature due to self-heating in two-terminal SrSnO3 thin film devices under electrical bias. Using pulsed current–voltage (I–V) measurements, thermal resistances of the thin films were determined by extracting the relationship between the channel temperature and the dissipated power. For a 26-nm-thick n-doped SrSnO3 channel with an area of 200 μm2, a thermal resistance of 260.1 ± 24.5 K mm/W was obtained. For a modest dissipated power of 0.5 W/mm, the channel temperature rose to ∼176 °C, a value which increases further at higher power levels. Electro-thermal simulations were performed which showed close agreement between the simulated and experimental I–V characteristics both in the absence and presence of self-heating. The work presented is critical for the development of perovskite-based high-power electronic devices.

    

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