Prof. Sanatan Chattopadhyay Profile

Prof. Sanatan Chattopadhyay

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Proceedings Article | 3 October 2022 Presentation + Paper

Oxygen mediated optical and electrical property modification of RF sputtered Ga2O3 thin films for photodetector application

Sangita Bhowmick, Rajib Saha, Madhuri Mishra, Arnab Mandal, Ankita Sengupta, Ankush Bag, Sanatan Chattopadhyay, Subhananda Chakrabarti

Proceedings Volume 12202, 1220204 (2022) https://doi.org/10.1117/12.2633278

KEYWORDS: Oxygen, Gallium, Thin films, Luminescence, Crystals, Photodetectors, Ultraviolet radiation, Heterojunctions, Deep ultraviolet, Argon

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The deep UV photodetectors (DUV-PDs) are technologically important for diverse applications, ranging from environmental monitoring, space communication etc. Among all solar blind materials Ga₂O₃ thin film shows its strong contention owing to its intrinsic solar-blind nature. However, the PD’s efficiency can be significantly affected by the defects such as oxygen vacancies (VO). Both the deficiency and surplus of oxygen during Ga₂O₃ thin film deposition can result in the formation of carrier scattering centers, sub-bandgap absorption, and leakage channels. In this work, we have studied the impact of oxygen flow rate (OFR) on the optical and electrical properties of RF sputtered Ga₂O₃ thin film. The Ga₂O₃ thin films were deposited on p-Si at room temperature, where the Ar to O₂ ratio has been varied from 1:0, 1:1, to 1:2 to maintain the O₂ poor and O₂ rich condition. The XRD spectrum shows the presence of two peaks positioned at ~33.0° , and ~64.5° , which are further identified as β(-202), and β(-313), respectively for samples grown without oxygen. The top view FESEM images confirm the uniform film growth for both O₂ rich conditions while some isolated bubble-like and grain-like structures are witnessed in ratios 1:0, and 1:1, respectively. The change in optical bandgap for all the samples is determined using diffuse reflectance spectra which show the bandgap values lie in the range of 4.1 eV-4.2 eV. Furthermore, the deconvoluted photoluminescence spectra (in the range of λ=300-500 nm) show the change in different types of V_o defects originating due to OFR induced structural asymmetry in the Ga₂O₃ thin film. Finally, the change in dark current in Ga₂O₃/p-Si heterojunctions is estimated from current-voltage (I-V) characteristics to understand the effect of OFR on its electrical properties for future DUV detectors.

Proceedings Article | 3 October 2022 Poster + Presentation + Paper

Investigation of selective rare-earth dopant (yttrium) incorporation on structural, optical, and unusual blue luminescence properties of ZnO nanowires

Rajib Saha, Madhuri Mishra, Sanatan Chattopadhyay, Subhananda Chakraborti

Proceedings Volume 12200, 122000D (2022) https://doi.org/10.1117/12.2633302

KEYWORDS: Zinc oxide, Nanowires, Zinc, Luminescence, Doping, Silicon, Absorption, Oxygen, Crystals, Yttrium

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In the current study, Y-doped vertically aligned ZnO nanowires are grown on p-Si substrates by employing cost-effective double-step chemical bath deposition technique. The doping percentages are varied systematically (Y_xZn_1-xO, x= 0.0, 0.01, 0.02, 0.03, 0.04 M) to investigate the impact of rare earth doping on structural, optical and luminescence properties of ZnO nanowires. The crystalline quality, morphology, optical absorbance and defect states of grown nanowires are studied extensively by employing XRD, FESEM, UV-VIS and room-temperature PL. XRD results reveal that Y-doped ZnO nanowires have single phase hexagonal structure without any extra peaks related to the Y-mixed oxides. FESEM analysis indicates that the dopant with higher radius dose not affected the morphology of ZnO nanowires. The optical energy band gaps of such nanowires are calculated by employing UV-VIS spectroscopy and values are estimated to be 3.11 eV to 2.97 eV. The absorption coefficient, reflective index and extinction coefficient are also extracted and analysed for all of such nanowires. PL results showed that the undoped ZnO nanowires exhibit low UV emission (374 nm) and relatively high green emission (552 nm), whereas, after a low amount of Y doping, UV emission peak enhanced along with an additional blue emission peak at 437 nm. Such blue emission peak is associated with the Zn interstitials related defects, which is generally responsible for the enhancement of donor concentrations in ZnO. Significantly, the oxygen vacancy related green emission peak reduces gradually with increasing Y incorporation. The work provides a detailed study on optical properties of Y-doped ZnO nanowires, which is essential for developing the next-generation heterojunction based optoelectronic devices.

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