Faculty Publications
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Item Detection of acceptor-bound exciton peak at 300 K in boron–phosphorus co-doped ZnMgO thin films for room-temperature optoelectronics applications(Elsevier B.V., 2021) Sushama, S.; Murkute, P.; Ghadi, H.; Pandey, S.K.; Chakrabarti, S.It is well-known that the ZnMgO thin-film faces a roadblock in its potential applications for various optoelectronic devices due to the limitation imposed on achieving p-type conduction. The mono-acceptor doping of ZnMgO endures from the stern self-compensation by native donor defects and deep acceptor level formation advocating the need for alternate doping techniques like co-doping. In this paper, we report a detailed study on the improvement in structural, elemental, and optical properties of phosphorus-doped Zn0.85Mg0.15O thin films, with an aim to obtain enhancement in the signatures of acceptor-doped behavior, under the influence of boron implantation time. In addition, the paper also captures the behavior exhibited by the co-doped samples as a result of the variation in the annealing temperature. The solubility of the phosphorus atom (acceptor dopant) was observed to improve with boron (donor co-dopant) implantation as confirmed by the structural, elemental, and optical properties of co-doped ZnMgO thin films. It was also found that the acceptor level emissions got improved after boron implantation in phosphorus-doped ZnMgO thin films. Additionally, with co-doping, the sample showed the signature of acceptor-bound exciton peak till 300 K, evidencing the room-temperature operability of the films. Moreover, the fabricated film had a shallow acceptor energy level located at around 74 ± 0.45 meV above the valence band. Co-doped samples also showed stable acceptor based optical emission for more than a year. © 2020 Elsevier B.V.Item Experimental investigation and comparative analysis of electron beam evaporated ZnO/MgxZn1-xO/CdxZn1-xO thin films for photodiode applications(Academic Press, 2021) Kumar, R.R.; Shukla, R.; Pandey, S.K.; Pandey, S.K.— This work reports the growth optimization and analysis of ZnO, MgxZn1-xO, and CdxZn1-xO thin films on silicon substrate using an electron beam evaporation system. The crystal phase purity, surface morphology, optical and electrical properties of deposited ZnO, MgxZn1-xO, and CdxZn1-xO thin films were studied. X-ray diffraction (XRD) spectra revealed that the deposited films were polycrystalline in nature with preferred (002) crystal orientation. Field emission scanning electron microscope study showed a dense-packed grained structure with an exact symmetrical distribution. The root-mean-square roughness of 3.03 nm was perceived by atomic force microscopy measurement for MgxZn1-xO thin-film, indicating good morphology of the deposited film. Photoluminescence measurement demonstrated a near-band-edge emission peak around 363 nm for ZnO thin film. The energy band gap obtained for ZnO, MgxZn1-xO, and CdxZn1-xO were 3.36 eV, 3.86 eV, and 2.89 eV, respectively, as measured by Ultraviolet–Visible spectroscopy. The higher amount of photocurrent was detected in illumination condition compared to dark condition with responsivity 0.54 AW-1 for ZnO films, making it suitable for photodiodes applications. © 2020 Elsevier LtdItem Phosphorus doping of ZnO using spin-on dopant process: A better choice than costly and destructive ion-implantation technique(Elsevier B.V., 2021) Mishra, M.; Sushama, S.; Pandey, S.K.; Chakrabarti, S.Radio frequency sputtered ZnO thin films doped with phosphorus (ZnO:P) have been prepared employing spin-on dopant process. In the SOD process, the dopant film has been spin-coated on a silicon substrate and positioned close to the as-deposited undoped ZnO film at high temperature to perform the phosphorus doping. The high-resolution X-ray diffraction measurement reveals that the prepared ZnO:P films are good in crystalline quality which improves further by annealing. It is found that the full-width half-maximum corresponding to (002) peak of SOD processed thin films is much narrower than previously reported ion-implanted thin films, indicating the better crystalline quality of SOD processed phosphorus-doped ZnO thin films. The X-ray photoelectron spectroscopy measurement signifies that the P2O5 decomposes into two phosphorus atoms behaving like an acceptor dopant and five oxygen atoms which may fill in oxygen vacancies at high-temperature annealing. The photoluminescence spectra discover the acceptor bound exciton peak at 3.35 eV and free electron to acceptor level transitions at 3.31 eV. The calculated acceptor binding energy is 127 meV for the phosphorus dopant which works as a shallow acceptor level. It is found that the phosphorus-doped ZnO thin films prepared using the SOD process have much superior structural and optical properties in comparison to previously reported ion-implanted film. This study demonstrates that the SOD process is much superior than the ion-implantation process to produce high-quality ZnO:P thin films for very stable p-type conduction. © 2021 Elsevier B.V.Item Enhancement in structural, elemental and optical properties of boron–phosphorus Co-doped ZnO thin films by high-temperature annealing(Elsevier B.V., 2021) Sushama, S.; Murkute, P.; Ghadi, H.; Pandey, S.K.; Chakrabarti, S.The inherent n-type nature of zinc oxide (ZnO) and its unstable p-type behavior with single dopant species have encouraged researchers to explore the effect of multiple dopants as a viable solution for long-term stability and repeatability. Herein, we report boron (B) and phosphorus (P) co-doped ZnO thin films engineered through an optimized ion implantation technique followed by annealing at 1000 °C in oxygen ambiance. We investigated their structural, chemical, and optical properties to capture the effect of both boron implantation duration and annealing temperature. Co-doping with boron was observed to boost phosphorus incorporation in the film. Compared with P-doping, P–B co-doping increased the dominance of acceptor-bound exciton peak and also, suppressed non-radiative/visible emission which is due to reduced Madelung energy. After high-temperature annealing at 1000 °C, further narrowing of optical emission peaks generated due to acceptor incorporation was observed. Also, the co-doped samples showed stability in the acceptor behavior for more than one year. © 2021 Elsevier B.V.Item Unfolding the conductivity reversal n- to p-type in phosphorus-doped ZnO thin films by spin-on dopant (SOD) process(Institute of Physics, 2022) Mishra, M.; Saha, R.; Bhowmick, S.; Pandey, S.K.; Chakrabarti, S.Phosphorus doping induced p-type doping in ZnO thin films based on spin-on dopant (SOD) process is reported in this article. Owing to the reduced dependence on the conventional amenities for diffusion/ion-implantation doping, the SOD process provides a simple and cheap doping method. The effect of SOD process temperature on conductivity ZnO thin films is investigated by altering the temperature from 700°C to 1000°C. Systematic field emission scanning electron microscopy analysis demonstrates the impact of doping temperature on the morphological properties of SOD. The x-ray diffraction measurements reveal that the p-type ZnO thin films had (002) preferred crystal orientation. At the same time, x-ray photoelectron spectroscopy validated the formation of the PZn-2VZn complex, which was responsible for the acceptor behaviour of films. Moreover, the photoluminescence spectra tracked down that the origin of 3.35 and 3.31 eV emission peaks is due to the acceptor bound exciton and free-electron to acceptor level transitions, respectively. Finally, an elevated hole concentration of 2.09 × 1016 cm-3 is achieved with a resistivity of 1.14 ω-cm at 800°C doping temperature. However, the film doped at 900°C and 1000°C showed n-type behaviour due to the generation of high concentration donor defects. Here, we successfully demonstrate that the SOD process has great potential to produce high-quality p-type ZnO thin films suitable for optoelectronic devices applications. © 2022 IOP Publishing Ltd.Item Investigation of phosphorus-doping of MgZnO thin films using efficient spin-on dopant process(Elsevier B.V., 2023) Mishra, M.; Saha, R.; Tyagi, L.; Sushama, S.; Pandey, S.K.; Chakrabarti, S.Phosphorus doped MgZnO thin films were prepared using the RF sputtering technique on a Si wafer, followed by spin-on doping (SOD) and annealing. The SOD is a cheap and non-destructive process in which the dopant film is spun on a Si wafer and placed in the vicinity of deposited undoped MgZnO thin film at a high temperature to perform doping. After doping, the MgZnO thin films were annealed at temperatures such as 700, 800, and 900°C, which significantly improved morphological, structural, and optical properties. The atomic force microscopy and scanning electron microscopy measurements revealed that phosphorus-doped MgZnO thin films annealed at 800–900°C have good morphology and large grains. X-ray diffraction spectra demonstrated the (002) orientation of MgZnO thin films. The photoluminescence spectra measured at 20 K demonstrated the acceptor bound exciton peak at 3.47 eV and acceptor binding energy of around 64.34 meV, indicating the formation of shallow acceptor levels by phosphorus doping of MgZnO thin films using the SOD process. In Raman spectroscopy measurement, the peak of E2high phonons mode of MgZnO wurtzite structure was observed around 436 cm−1. The FWHM value of this peak reduces with augmentation annealing temperature, demonstrating improvement in crystallinity. X-ray photoelectron spectroscopy measurement demonstrated the presence of phosphorus atoms in the SOD processed MgZnO thin films, which is again verified by Fourier-transform infrared spectroscopy measurement showing vibration modes of P–O bonds. It was observed that the different properties of SOD-prepared phosphorus-doped MgZnO films were superior to the film prepared using the alternate costly and destructive ion-implantation technique. These findings have revealed that high-quality phosphorus-doped p-type MgZnO thin films by the SOD process are very suitable for UV optoelectronic device applications. © 2023 Elsevier B.V.Item Design and fabrication of all-inorganic transport materials-based Cs2SnI6 perovskite solar cells(Springer, 2023) Kumari, D.; Jaiswal, N.; Shukla, R.; Punetha, D.; Pandey, S.K.; Pandey, S.K.With lead-based perovskite materials, lead content and long-term stability are the big concerns. Recently, Cesium tin iodide (Cs2SnI6) double perovskite has gained recognition as a stable and environment-friendly photovoltaic material compared to lead-based perovskite materials. In the present study, we have investigated Cs2SnI6 based solar cell with all inorganic transport materials using SCAPS-1D. The optimized device exhibited a maximum efficiency of about 18%. Further we fabricated Cs2SnI6 perovskite films using a solution process approach, utilizing CsI and SnI4 in a 2:1 ratio. For synthesized double perovskite film, the crystallinity, morphologies, and optical characteristics were examined. Additionally, the stability analysis confirmed that the prepared perovskite films were stable for more than two months under ambient exposure. Finally, utilizing the synthesized Cs2SnI6 thin films as an absorber material, we fabricated two solar cells without and with hole transport layer (HTL), having configurations of glass/FTO/ZnO/Cs2SnI6/Ni and glass/FTO/ZnO/Cs2SnI6/ MoS2/Ni, respectively, in the ambient conditions. As a major finding, it has been observed that the inclusion of MoS2 as HTL improved overall performance, with an enhancement in the power conversion efficiency (PCE) of nearly 45% compared to the device without HTL. © 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.