E. A. Mastio

The effects of KrF pulsed laser and thermal annealing on the crystallinity and surface morphology of radiofrequency magnetron sputtered ZnS:Mn thin films deposited on Si

Thin films of ZnS:Mn (800 nm) have been deposited by rf magnetron sputtering onto 100 mm diam n-type single-crystal (100) Si wafers. Specifically for use as active layers in thin film electroluminescent devices, the films need a postdeposition annealing treatment to enhance their luminescent properties. Inherent to the later process step are structural modifications of the phosphor layer which form the basis of this study. Both pulsed laser and thermal postannealing techniques have been investigated. Reported are the induced crystalline and surface morphology modifications via x-ray diffraction and atomic force microscopy analysis. As-grown and thermally treated films were cubic in nature and no significant grain growth or reorientation occurred while heating up to 700 °C. Pulsed (∼ 20 ns duration) KrF laser treated samples were annealed at power densities from 10.76 to 24.27 MW/cm2 under 10.34 bar of argon pressure. Beam quality and diagnostics were emphasized during laser irradiation with particular attention brought to energy and pulse duration measurements. It has been demonstrated that at the power densities used, a gradual phase transition from cubic to hexagonal is occurring while the average crystallite size remains constant. Surface analysis highlights concomitance between the phase transition and the smoothening of the irradiated surface. A one dimensional thermal model of the pulsed laser annealing process shows that a surface temperature for crystalline ZnS equating to the transition temperature should be reached at 17 MW/cm2, significantly below the numerically evaluated melting threshold of 30.5 MW/cm2. Combining experimental and theoretical results, it is concluded that the phase transition occurs in the solid state.Thin films of ZnS:Mn (800 nm) have been deposited by rf magnetron sputtering onto 100 mm diam n-type single-crystal (100) Si wafers. Specifically for use as active layers in thin film electroluminescent devices, the films need a postdeposition annealing treatment to enhance their luminescent properties. Inherent to the later process step are structural modifications of the phosphor layer which form the basis of this study. Both pulsed laser and thermal postannealing techniques have been investigated. Reported are the induced crystalline and surface morphology modifications via x-ray diffraction and atomic force microscopy analysis. As-grown and thermally treated films were cubic in nature and no significant grain growth or reorientation occurred while heating up to 700 °C. Pulsed (∼ 20 ns duration) KrF laser treated samples were annealed at power densities from 10.76 to 24.27 MW/cm2 under 10.34 bar of argon pressure. Beam quality and diagnostics were emphasized during laser irradiation with particular att...

Pulsed KrF laser annealing of ZnS : Mn laterally emitting thin film electroluminescent displays

Abstract Pulsed KrF (248-nm) laser annealing was investigated as a post-deposition process for RF sputtered ZnS:Mn phosphor layers used in laterally emitting thin film electroluminescent (LETFEL) displays. LETFEL devices consist of a phosphor layer sandwiched between two insulating thin films (Y 2 O 3 ), grown onto silicon substrates patterned with micro-mirrors (SiO 2 ). The micro mirror structure permits surface viewing by reflecting laterally emitted light due to internal waveguiding effects. Laser irradiation of the uncoated phosphor layer was performed using KrF excimer 248-nm laser pulses of 20 ns under an argon overpressure of 10.34 bars to limit laser ablation. The influence of the laser irradiation fluence on the LETFEL performance was investigated from 0.3 to 1.5 J/cm 2 . In this paper, we have reported the brightness-voltage characteristics of laser annealed, non-annealed and thermally annealed devices at 500°C for ∼1 h. It is shown that the onset for light emission (threshold voltage) decreases with laser annealing. Using this novel method of annealing, the brightness of LETFEL devices is observed to increase with increasing laser fluence.

Pulsed laser annealing for high-efficiency thin film electroluminescent devices

Thin film electroluminescent (TFEL) structures composed of ZnS:Mn (phosphor) and Y2O3 (insulator) films were annealed using pulsed (∼20 ns) KrF laser irradiations under an environment of 150 psi (∼10.34 bars) of argon. The crystallinity of both layers was studied via x-ray diffraction analysis. Their degree of lattice misfit and the integrated diffraction line intensities were examined to assess the thermal effects of pulsed laser annealing. In agreement with a thermal model of the laser–matter interaction and previous results, we suggest that the pulsed laser annealing technique improves the luminescent efficiencies of thin film electroluminescent phosphors by generating an in-depth solid-state phase transition. We report that the laser processed TFEL structure exhibits better display performance than equivalent devices thermally annealed at a temperature of 450 °C as demonstrated by sharper turn-on response and also an increase in brightness by a factor greater than four times. We attribute these perfor...

Ablation study on pulsed KrF laser annealed electroluminescent ZnS:Mn/Y2O3 multilayers deposited on Si

The ZnS:Mn active layer of a thin film electroluminescent (TFEL) device has been annealed under 1.034 MPa (10.34 bar, 150 psi) of argon pressure using a 20-ns pulsed KrF excimer laser. We investigate the effects of multiple shots at various power densities upon the ablation rates of the ZnS:Mn layer. The results are compared to a thermal simulation of the laser-matter interaction using single pulse irradiation, and it is inferred that the cubic to hexagonal transition and melting of ZnS:Mn decrease the ablation rate.

The effects of multiple KrF laser irradiations on the electroluminescence and photoluminescence of rf-sputtered ZnS:Mn-based electroluminescent thin film devices

Multiple pulse KrF laser annealing and ablation effects upon the luminescent properties of ZnS:Mn-based electroluminescent structures are investigated. The beneficial increase of the number of active luminescent centres is assessed via sub-bandgap photoluminescence analysis and an optimum is determined due to the competition of the annealing and ablation processes. The maximal photoluminescence signals obtained via laser treatment are 67% and 19% greater than the signals obtained from samples thermally annealed for 1 h at 500°C and 700°C, respectively. Under certain irradiation conditions, the electroluminescence analysis of laser-annealed samples also shows enhanced values compared with samples treated thermally at 500°C. However, these improvements do not reflect those expected from the photoluminescence analysis. We suggest that multiple pulse irradiation leads to detrimental modifications at the electronic interface for electroluminescence applications.

Pulsed KrF laser annealing of RF sputtered ZnS:Mn thin films

Abstract Pulsed KrF laser annealing (PLA) of ZnS:Mn thin (800 nm) film phosphors has been investigated as an alternative to thermal annealing for the fabrication of electroluminescent devices. The influence of the surrounding gas pressure during exposure, the energy density (Ed) of the laser beam and the effect of double irradiation is reported. Luminescent properties as function of laser energy density (Ed) are determined via photoluminescent (PL) characterisation. Energy densities used vary from 53 to 777 mJ/cm 2 . PL intensities are determined to be linearly dependent with Ed beyond a threshold of 150 mJ/cm 2 and maximum PL enhancement is a factor of 2.1 x . A thermal simulation of the PLA process suggest that PL improvement is proportional to deposited thermal energy and this in the solid state. The calculated melting threshold agrees well with previous work.

P-169: Optimization of the Electrical and Optical Properties of Ink-Jet-Printed SnO(2):Sb using Thermal Annealing and Excimer-Laser Processing

Sb doped SnO2 has been formulated and inkjet printed onto borosilicate glass substrates. The resultant films have been post processed using traditional thermal annealing up to 440°C and laser processing with a KrF excimer laser (λ = 248nm). Sheet resistance values of 700Ω/□ have been achieved with thermal annealing, whilst transparency remains >85% in the visible region. As a result of laser processing significant decreases in sheet resistance of the inkjet printed layers have been demonstrated indicating the viability of inkjet printing onto flexible substrates. The optical transmittance of the laser processed films has been shown to remain >85%. Initial measurements indicate that thermal and laser post processes reduce surface roughness.

Lattice misfit versus performance of thin film electroluminescent structures

Thin polycrystalline electroluminescent thin films (TFEL) of ZnS:Mn (phosphor) and Y2O3 (insulator) were deposited individually or as multilayers onto Si (100) substrates. Their crystallinity and the luminescent efficiency of the phosphor films were investigated at varying thermal annealing temperatures. It is shown that the luminescent quality of the phosphor layer increases up to 700 °C, whereas the electroluminescence operating intensity of TFEL devices saturates at 500 °C. The structural analysis of the insulating and phosphor layers shows that they recrystallize at annealing temperatures of, respectively, 500 and 600 °C, and that their lattice misfit doubles at processing temperatures>=500 °C. Since TFEL devices should benefit from enhanced luminescence efficiency and crystallinity at high annealing temperatures, we suggest that the lack of improvement in device performance beyond 500 °C is due to interface alterations. According to previous works, we propose that the lattice misfit increase between ...