Faculty Publications
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Item Doping of ZnMgO with phosphorus by spin-on dopant technique(SPIE, 2021) Mishra, M.; Sushama, S.; Pandey, S.K.; Chakrabarti, S.Zinc magnesium oxide is a ternary compound wide bandgap semiconductor. Incorporation of Mg into ZnO helps in increasing the of p-type conductivity by affecting the background n-type nature of ZnO. This is possible because Mg incorporation in ZnO elevates the conduction band edge which in turn increases the distance between the shallow donor level and conduction band minima, resulting increase of activation energy for background donor. In this work, we report Spin-on Dopant technique to dope phosphorus in Zn0.85Mg0.15O lattice. The undoped ZnMgO thin film (sample A) was deposited using RF sputtering. The SOD sample (sample B) was prepared using P509 spin on dopant and kept approximate 1cm above ZnMgO film at 600°C for four hours. The doped sample was annealed at temperature 700°C (sample C) in oxygen ambient to see the high temperature annealing effect on doping. In studies of high-resolution x-ray diffraction, a dominant (002) peak was observed in sample A, B, and C at 34.173°, 34.624°, and 34.638° respectively. The shifting of (002) peak at higher angle for doped samples indicates the phosphorus doping in film. The XPS spectra of phosphorus 2p peak are appears at ∼134 eV indicates the presence of P atoms as P-O bonds in ZnMgO lattice. The Donor-Acceptor pair (DAP) transition peak around 3.473eV and free Acceptor (AX°) peak around 3.588eV were found in photoluminescence spectra of sample B revels the phosphorus doping in ZnMgO. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.Item Improvement in optical and elemental properties of spin-on phosphorus doped ZnO film(SPIE, 2021) Mishra, M.; Sushama, S.; Pandey, S.K.; Chakrabarti, S.SOD is a type of conventional doping technique where diffusion of dopant atom takes place from the liquid source to film by thermal annealing of sample. The study shows the SOD process is a cost effective, less destructive and an efficient way to dope ZnO film. We have doped ZnO films with phosphorus atom by simply annealing it in atmospheric furnace up to 600°C for 4 hrs. After in-situ annealing SOD process, sample has also been ex-situ annealed at 900°C in oxygen ambient for 10 secs. The elemental analysis of phosphorus 2p peak at 132.62 eV ensures the existence of P-O bond for doped sample which shows phosphorus replacing Zn and bonding with oxygen in to the lattice in order to make Pzn-2Vzn an acceptor complex. The doped samples showed the photoluminescence peak at 3.32eV and 3.35eV, which attributed to free electron to acceptor (FA) and acceptor-bound exciton (A0X) energy as an evidence of acceptor doping in ZnO film. The ex-situ annealing of doped sample further improves in passivation of deep level defects of film. All sample has (002) orientation, and a compressive stress to be found in the doped sample due to phosphorus replacing Zn, are confirmed by analysis of XRD results. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.Item Room-temperature ultraviolet-ozone annealing of ZnO and ZnMgO nanorods to attain enhanced optical properties(Springer, 2020) Alam, M.J.; Murkute, P.; Sushama, S.; Ghadi, H.; Mondal, S.; Paul, S.; Das, D.; Pandey, S.K.; Chakrabarti, S.ZnO and ZnMgO nanorods have proven to be promising materials for sensing, UV and deep UV based optoelectronic applications. A major drawback of ZnO and ZnMgO based thin films and nanorods is the presence of native point defects which deteriorates their optical efficiency and becomes an impediment to their efficient device applications. The furnace and rapid thermal annealing processes have overcome this up to a great extent but being high temperature processes, they put many fabrication and technological limits in device fabrication. Especially keeping an eye on the future flexible devices, herein we report ultraviolet-ozone (UVO) annealing as a room-temperature, simple and cost-effective annealing method to improve the optical efficiency of ZnO and ZnMgO nanorods along with control of defect states. The ZnO and ZnMgO nanorods were grown by hydrothermal method and annealed in UVO irradiation. UVO annealing substantially improved near band emission and suppressed defect band emissions. It is found that zinc interstitial atoms migrate from the top portion of ZnO nanorods towards the bottom of nanorods after UVO annealing, resulting in reduced zinc interstitial defects in the top portion of nanorods. X-ray diffraction results showed improvement in structural properties. XPS results confirmed suppression of oxygen vacancies and zinc interstitials and improvement in lattice oxygen in the ZnO nanorods after UVO annealing. Optimum times of UVO annealing for ZnO and ZnMgO nanorods were 30 and 50 min respectively. These findings will be helpful for the further development of ZnO and ZnMgO nanorods based high performance optoelectronic devices and sensors. © 2020, Springer Science+Business Media, LLC, part of Springer Nature.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 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 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.