Self-powered photodetectors have been fabricated from a single germanium nanowire (NW) in the metal-semiconductor-metal (MSM) device configuration. The self-powered devices show a high photoresponse (responsivity ∼ 10-10 A W) in the wavelength range 300-1100 nm. It has been established from I-V characteristics that asymmetry exists in the Schottky barrier height (SBH) at the two MS contacts. We have used simulation to establish that the asymmetric SBH at the metal contacts in an MSM device is a major cause for the 'built-in' axial field that leads to separation of a light generated electron-hole pair in the absence of an applied bias. Thus, even in the absence of external bias, the photogenerated carriers can be separated, which then diffuse to the appropriate electrodes driven by the 'built-in' axial field. We also point out the physical origins that can lead to unequal barrier heights in seemingly identical NW/metal junctions in a MSM device.
We report smart color-sensing devices of two-dimensional lead halide perovskites that exhibit a graded band gap across the film. We observe that the device short-circuit photocurrent is strongly dependent on excitation wavelength λ, and this arises through photoabsorption at different depths in the sample due to the graded bandgaps present. This λ signature in the response of the device is observed in case of steady-state excitation when incident from the high bandgap side of the film, where a complete reversal in the polarity of the photocurrent I ph (t) is obtained as the excitation wavelength is spanned across the visible spectrum. The transient photocurrent reveals λspecific response arrived from a combination of positive and negative I ph (t) components. The uniqueness of I ph (t) as a function of incident λ can be utilized to examine spectral purity without dispersive optical elements. An equivalent circuit model description provides a possible glimpse into the physical sources involved in contributing to these features.
gradually implemented for many combination of semiconductors. [24][25][26][27] The difference in the signal from the two arms has a characteristic spatial profile which represents the PSD, and is used to determine the position. The microscopic device physics relies on the lateral photoeffect developed due to difference in the charge collection rates at the indium tin oxide (ITO)-perovskite interface and the Au electrode upon nonuniform illumination. Lateral photovoltage (LPV) developed due to this specific device structure drives the photoexcited carriers toward the counter electrodes on the two arms. Earlier work from our laboratory demonstrated the PSD concepts using polymer semiconductors and their ability to form Schottky interface with Al cathodes. [28] HOIP system offers considerable advantage over polymers with regard to quantum yield, trap density, monomolecular recombination rates, and carrier mobility. [29,30] This effectively translates into a higher LPV in HOIP devices. We explore the possibility of PSD based on HOIP and tailor the device geometry accordingly.
We demonstrate a single-step fabrication process of highly stable and luminescent polymer fibers embedded with quantum dots (QDs) of the organic−inorganic hybrid perovskite (OIP) (CH 3 NH 3 PbBr 3 ) using the electrospinning process. The fiber (∼2 μm diameter) primarily consists of poly(methyl methacrylate) dispersed with clusters of OIP quantum dots. The OIP clusters are radially distributed, normal to the fiber axis. The photoluminescence quantum yield (PLQY) is high (∼80%) and comparable to that of conventional QDs. The emission maxima are tunable by varying the concentration of OIP precursor in the electrospinning solution. Submicron emission maps show an isotropic and continuous emission along the fiber, suggesting uniform distribution of QD clusters. Temperature-dependent PL response indicates features which are a function of the particle size. For small QDs, the PLQY(T) maxima are close to the ambient temperature, whereas the PLQY(T) maxima shift sizably to T < 50 K for larger QDs. Significant waveguiding of QDs emission and amplified spontaneous emission, a prerequisite for lasing, were observed in the fiber confined OIP system at room temperature.
We present experimental evidence showing that the effective carrier diffusion length L d and lifetime τ depend on the carrier density in MAPbBr 3 single crystals. Independent measurements reveal that both L d and τ decrease with an increase in photocarrier density. Scanning photocurrent microscopy is used to extract the characteristic photocurrent I ph decay-length parameter L d , which is a measure of effective carrier diffusion. The L d magnitudes for electrons and holes are determined to be ∼13.3 and ∼13.8 μm, respectively. A marginal increase in uniform light bias ( 5 × 10 15 photons/cm 2 ) increases the modulated photocurrent magnitude and reduces the L d parameter by a factor of 2 and 3 for electrons and holes, respectively, indicating that the recombination is not monomolecular. The L d variations are correlated to the features in photoluminescence lifetime studies. Analysis of lifetime variation shows intensity-dependent monomolecular and bimolecular recombination trends with recombination constants determined to be ∼9.3 × 10 6 s −1 and ∼1.4 × 10 −9 cm 3 s −1 , respectively. Based on the trends of L d and lifetime, it is inferred that the sub-band-gap trap recombination influences carrier transport in the low-intensity excitation regime, while bimolecular recombination and transport dominate at high intensity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.