High band gap (3.34 eV) and large exciton binding energy (60 meV) at room temperature facilitates ZnO as a useful candidate for optoelectronics devices. Presence of zinc interstitial and oxygen vacancies results in n-type ZnO film. Phosphorus implantation was carried out using plasma immersion ion implantation technique (2kV, 900W) for constant duration (50 s) on RF sputtered ZnO thin films (Sample A). For dopant activation, sample A was subjected to Rapid Thermal Annealing (RTA) at 700, 800, 900 and 1000°C for 10 s in Oxygen ambient (Sample B, C, D, E). Low temperature (18 K) photoluminescence measurement demonstrated strong donor bound exciton peak for sample A. Dominant donor to acceptor pair peak (DAP) was observed for sample D at around 3.22 eV with linewidth of 131.3 meV. High resolution x-ray diffraction measurement demonstrated (001) and (002) peaks for sample A. (002) peak with high intensity was observed from all annealed samples. Incorporation of phosphorus in ZnO films leads to peak shift towards higher 2θ angle indicate tensile strain in implanted samples. Scanning electron microscopy images reveals improvement in grain size distribution along with reduction of implantation related defects. Raman spectra measured A1(LO) peak at around 576 cm-1 for sample A. Low intensity E2 (high) peak was observed for sample D indicating formation of (PZn+2VZn) complexes. From room temperature Hall measurement, sample D measured 1.17 x 1018 cm -3 carrier concentration with low resistivity of 0.464 Ω.
ZnO has potential application in the field of short wavelength devices like LED’s, laser diodes, UV detectors etc, because of its wide band gap (3.34 eV) and high exciton binding energy (60 meV). ZnO possess N-type conductivity due to presence of defects arising from oxygen and zinc interstitial vacancies. In order to achieve P-type or intrinsic carrier concentration an implantation study is preferred. In this report, we have varied phosphorous implantation time and studied its effect on optical as well structural properties of RF sputtered ZnO thin-films. Implantation was carried out using Plasma Immersion ion implantation technique for 10 and 20 s. These films were further annealed at 900°C for 10 s in oxygen ambient to activate phosphorous dopants. Low temperature photoluminescence (PL) spectra measured two distinct peaks at 3.32 and 3.199 eV for 20 s implanted sample annealed at 900°C. Temperature dependent PL measurement shows slightly blue shift in peak position from 18 K to 300 K. 3.199 eV peak can be attributed to donoracceptor pair (DAP) emission and 3.32 eV peak corresponds to conduction-band-to-acceptor (eA0) transition. High resolution x-ray diffraction revels dominant (002) peak from all samples. Increasing implantation time resulted in low peak intensity suggesting a formation of implantation related defects. Compression in C-axis with implantation time indicates incorporation of phosphorus in the formed film. Improvement in surface quality was observed from 20 s implanted sample which annealed at 900°C.
Zn 0.85Mg 0.15O a promising material for the future in the area of the optoelectronic devices due to the flexibility of changing bandgap. The impact of thermal annealing on Zn 0.85Mg 0.15O thin films grown by RF sputtering on intrinsic Si substrate by RF sputtering at constant temperature 400°C. During deposition gas flow 80% Argon and 20% oxygen was used. The samples were rapid thermal annealed at 900°C (20 sec) and 950°C for 20 and 30 sec to yield samples A, B and C, respectively. Low temperature photoluminescence (PL) measurements show presence of violet emission around 3.1 eV in as-grown sample due to the presence of zinc interstitial defects. Near-band-edge emission was found at around 3.65 eV for sample A. However, for sample B this peak was redshifted and found around 3.63 eV but with much higher intensity. Further increase on annealing time (30 sec) sample was further red-shifted (sample C). On comparing with sample a, sample B showed 3 times enhancement in PL intensity and 30 times enhancement compared to as grown sample. X-ray diffraction measurements confirmed the growth of highly c-axis oriented <002> Zn 0.85Mg 0.15O thin films for all samples. Uniform lattice constant (a= 0.29 and c= 0.51 nm) was achieved for all annealed samples. The <002> peak for all annealed samples shows higher intensity in comparison with the as-grown. A slight shift in the peak was observed which is due to presence of strain. For sample B surface roughness were measured 6.34nm.
ZnO is gaining substantial interest day by day because of its wide bandgap (3.4 eV) and large exciton binding energy (60 meV) due to which lasing emission is possible from ZnO based materials even above room temperature. Here we are reporting the influence of growth temperature and annealing ambient on photoluminescence properties, crystalline size and surface morphology of ZnO thin films deposited on Si substrates at 200°C by RF sputtering. Achieved thickness is 198 nm as confirmed by Profilometer. Grown samples were further rapid thermal annealed at 800°C in Ar, N2, O2, and in vacuum ambient. The as-grown sample did not exhibit any near band edge emission peak due to presence of deep level defects. Low temperature (18 K) photoluminescence spectra exhibited strong emission peak around 3.32 eV when the as-grown sample was annealed at 800° C in oxygen ambient which indicates defects state passivation. A lowest full width half maximum (FWHM) of 73.85meV was achieved for sample annealed in O2 ambient .Sample annealed in vacuum showed peak with highest intensity at 3.25eV, which corresponds to donor-bound-acceptor (DAP). High resolution Xray diffraction measurement exhibited a dominant <002> peak. Atomic Force Microscopy also revealed surface roughness of 7.72 nm for sample annealed in O2 ambient.
In this paper we report a detailed investigation of ZnO thin film properties deposited on Si<100> substrate at 400°C using RF sputtering. To reduce oxygen induced vacancies and interstitial defects in samples, variable oxygen flow rate during deposition followed by post growth annealing in oxygen ambient were carried out. Four samples were deposited under constant temperature condition but with variable oxygen partial pressure of 0%, 20%, 50% and 80% in Argon and Oxygen mixture, namely sample S1, S2 , S3 and S4 respectively. Deposited films were further annealed at 700, 800, 900 and 1000°C in oxygen ambient for 10s. Photoluminescence (PL) measurements carried at low temperature (18K) demonstrated near band edge emission peak of ZnO at 3.37eV. Increment in PL intensity was observed with increasing annealing temperature and a particular sample S4 annealed at 900 measured narrowest full width half maxima (FWHM) of ~0.1272eV. Defects peaks observed at lower energies were suppressed with increasing oxygen flow and post growth annealing, indicating improvement in film quality. From HRXRD measurement it was observed S4 sample annealed at 900°C has the highest peak intensity and narrowest FWHM compared to other samples, demonstrating the best crystalline property of annealed film at 900°C. Highest XRD peak intensity measured at 34.53° corresponds to (002) crystal orientation reveals that the films were highly caxis oriented. AFM results show increase in grain size with increasing oxygen flow and annealing temperature which ensures improvement in morphological properties of the film.
ZnO is a highly efficient and promising semiconductor material because of its large bandgap (3.37 eV) and exciton binding energy (60 meV). MgO also has a very high bandgap (7.8 eV), and the incorporation of Mg into ZnO can result in an alloy with a bandgap of more than 4 eV . We used plasma immersion ion implantation to dope phosphorus into Zn0.85Mg0.15O for achieving p-type ZnMgO. RF sputtering was used to deposit ZnMgO on a Si substrate. Phosphorus doping was conducted from 10 s to 70 s. Rapid thermal annealing of the samples was performed to remove any implantation defects. A highly dominant acceptor-bound-exciton peak was observed at 3.36 eV by photoluminescence measurements, which continued to dominate from low temperature to room temperature. Donor-bound acceptor and free-electron acceptor peaks were also observed at 3.24 eV and 3.28 eV, respectively.
The optical and structural characteristics of H− ion-implanted ZnMgO were investigated by temperature-dependent photoluminescence (PL) and high-resolution X-ray diffraction (HRXRD). Low-energy (40 keV and 50 keV) hydrogen implantation was performed on RF-sputter-deposited ZnMgO thin films by varying the fluences from 1013 ions/cm2 to 5 × 1014 ions/cm2 . Highly c-axis-oriented <002> ZnO films were observed for all samples, as confirmed by HRXRD. A gradual decrease in the acceptor concentration was observed with increasing fluence, as confirmed by low-temperature PL results. This suggests that hydrogen atoms act as a shallow donor.
The large bandgap (3.37 eV) and exciton binding energy (60 meV) makes ZnO most promising material in the area of
optoelectronic devices. The efficiency of these devices can be enhanced by increasing the bandgap of those materials
which is possible by band-gap engineering. It has been found that incorporation of Mg can increase the bandgap of the
alloy up to 4 eV and even more. We investigated the optical properties of Zn1-x MgxO film implanted by Li at low energy (40 KeV) with dosage of 5x1013 ions/cm2 and 1014 ions/cm2 respectively. Prior to implantation 150 nm Zn1-x MgxO (x=0.15) film was deposited on Si substrate followed by annealing at 650°C and 750°C. For dosage of 5x1013 ions/cm2 and 1014 ions/cm2 the low temperature (15K) and room temperature photoluminescence spectra is dominated by the
emission of 3.66 eV which is the band gap energy of Zn1-xMgxO, shifts to 3.63 eV at higher dosage of ions. With increasing energy (50 KeV) this peak was revealed only at 5x1013 ions/cm2. At 1014 ions/cm2 no sign of this peak was visible. The splitting of conduction band and valence band into multiple sub-bands causes a transition between the subband of conduction band and sub-band of heavy-hole and an emission occurs at 3.58 eV referred as 11H. The existence of acceptor-bound exciton peak (A°X) around 3.33 eV and the presence of donor-to-acceptor-pair peak at 3.24 eV provide strong evidence of increased acceptor concentration.
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