Authors: S. Kubota | Chisato Muto | Tatsuya Kameyama | Susumu Kuwabata | Tsukasa Torimoto
Source: ECS Meeting Abstracts (article, 2024-11-22)
Field: Materials Science — Materials Chemistry

Fabrication of Near-Infrared Photodetectors with Ag-Cu-in-Te Nanorod Films as an Active Layer Semiconductor nanocrystals (NCs) have been intensively investigated for the application to photovoltaics, light-emitting diodes, and biological markers, because of their tunable light absorption and excellent light emission properties. In our previous paper [1] , we reported the synthesis of near-IR-responsive AgInTe 2 NCs by a colloidal method, in which the obtained NCs showed a relatively sharp photoluminescence (PL) peak at 1100 nm with a quantum yield of 47%. In addition, solid solution NCs of ZnTe and AgInTe 2 were found to have tunable energy gap ( E g ) in the wide near-IR region from 1.2 to 1.6 eV by controlling their chemical composition [2] . Here, we explore CuInTe 2 , an I-III-VI semiconductor with the E g of 0.86 eV, aiming to achieve E g control in a narrower range from 0.86 to 1.2 eV by forming solid solutions with AgInTe 2 . This paper reports the solution-phase synthesis of Ag (1- x ) Cu x InTe 2 (ACITe) solid solution NCs and evaluates their optical detection capabilities for near-IR light. We demonstrate that the particle size and composition of ACITe NCs can be modified to fine tune their photochemical properties. Metal acetates of Ag, Cu, and In were added to 1-dodecanethiol in a test tube and stirred at room temperature under a nitrogen atmosphere. Trioctylphosphine telluride (TOP-Te) was added to the mixture and heated at 180°C for 10 min with vigorous stirring. The resulting ACITe NCs were isolated and purified, followed by dissolving in octane. A seed-mediated crystal growth method was used to control the particle size: The thus-obtained ACITe NCs were added as a seed and further heated with 1-dodecanethiol containing corresponding metal acetates and TOP-Te. The size of NCs was controlled by changing the amount of ACITe seeds added. ACITe NCs were rod-shaped particles, regardless of their chemical composition, Cu/(Ag+Cu) (= x). The XRD pattern of NCs prepared with x= 0 was attributed to hexagonal AgInTe 2 crystal structure. As the Cu fraction increased, i.e. the x value increased, each peak in the XRD pattern of ACITe NCs was shifted to a higher angle, approaching that of tetragonal CuInTe 2 crystal structure. These results indicated that the thus-obtained NCs were composed of a solid solution between AgInTe 2 and CuInTe 2 , the composition of which was controlled by the Cu/Au ratio in the precursors. With the elongation of the rod NCs, the XRD peak around 25° corresponding to the hexagonal (002) plane became narrowed, indicating that ACITe NCs were grown along with the c-axis of hexagonal crystal structure. The onset wavelength of the absorption spectra of ACITe NCs gradually shifted from 1070 nm ( x = 0, AgInTe 2 ) to 1200 nm ( x =1, CuInTe 2 ) with increasing the x value, indicating that E g of ACITe NCs was tuned in the near-IR region by controlling their composition . The obtained ACITe NCs ( x = 0.5) with average rod lengths of 13 nm, 23 nm, and 27 nm (denoted as ACITe(13 nm), ACITe(23 nm), and ACITe(27 nm), respectively) were used to fabricate a photodetector, in which the QDs were spin-coated on a comb-shaped electrode. We evaluated the photoresponse at the applied voltage of +5.0 V under a dark condition or under the irradiation of near-IR light (880 nm) with various intensities. Regardless of the light intensity, the devices prepared with ACITe(23 nm) and ACITe(27 nm) exhibited approximately 5-7 times higher sensitivity compared to that with ACITe(13 nm), indicating that the crystal morphology of semiconductor NCs significantly affected their performance of near-IR light detection. Moreover, the photosensitivity at the irradiation intensity of 20 µW cm -2 was 20.3 A W -1 for the device with ACITe(27 nm), which was higher than that reported for a photodetector fabricated with conventional near-IR-responsive PbSe NCs (0.66 A W -1 ; 1064 nm, 10 µW cm -2 ) [3] . References (1) T. Kameyama, et al., Nanoscale , 8, 5435 (2016). (2) T. Kameyama, et al., J. Mater. Chem. C , 6, 2034 (2018). (3) A. A. Babaev, et al., Nanomaterials, 13, 3051 (2023). Nanorod ; Materials science ; Photoluminescence ; Quantum yield ; Semiconductor ; Band gap ; Solid solution ; Absorption (acoustics) ; Analytical Chemistry (journal) ; Optoelectronics ; Nanotechnology ; Chemistry ; Optics ; Fluorescence Quantum Dots Synthesis And Properties ; Chalcogenide Semiconductor Thin Films