Ionizing radiation effect of gamma ray and neutron flux On n-ZnO/pCuGaO2 Heterojunction Diode for flexible space electronics application
Space electronics based on invisible circuitry requires both transparent n-type and p-type oxide-based semiconductor materials as active channel layers to make circuit design more flexible. However, in space, semiconductor devices are vulnerable to various effect of high energy level of radiation ca...
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| Format: | Thesis |
| Language: | English |
| Published: |
2019
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| Subjects: | |
| Online Access: | https://eprints.ums.edu.my/id/eprint/25110/1/Ionizing%20radiation%20effect%20of%20gamma%20ray%20and%20neutron%20flux.pdf |
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| Summary: | Space electronics based on invisible circuitry requires both transparent n-type and p-type oxide-based semiconductor materials as active channel layers to make circuit design more flexible. However, in space, semiconductor devices are vulnerable to various effect of high energy level of radiation causing single event upsets (SEU), damaging or altering the lattice structure. In this work, n-ZnO/pCuGaO2 was selected due to its relatively wide bandgap and a visibility transmittance up to 75%, has wide bandgap of II-VI semiconductor group (~3.3- 3.4 eV), a high electron mobility, easily fabricated under low temperature, an efficient photon emission and high conductivity. P-CuGaO2 and n-ZnO thin films were deposited by using radio frequency (RF) powered sputtering method on indium tin Oxide (ITO) with a base pressure of 9x10-3 Torr, at 300 °c deposition temperature, an Argon gas flow of 10 seem, a radio frequency power of 100 Watt and deposition time of 30 minutes. Once the deposition of the active and confining layer has been fabricated, a silver (Ag) paste was applied as the contacting layer. Structural morphology, optical and electrical properties of both n-ZnO/p-CuGaO2 thin film and heterojunction diode were investigated before and after irradiation. Fabricated samples were then irradiated at SINAGAMA and NUR II facility. The samples were irradiated using Cobalt-60, gamma-ray with a dose ranging from 10 kGy to 200 kGy and separately a neutron flux of 2xl014 n/cm2, 9.5 x1014 n/cm2 and 6.5x101s n/cm2. The structural properties reveal that p-CuGaO2 and n-ZnO films, shows the degradation of grain size after irradiation and has a lower diffractionpeak · with an increase in the Full width half maximum (FWHM). The optical properties of deposited p-CuGaO2 thin film and n-ZnO, exhibits approximately 75%and 80% respectively in the invisible region at pre-irradiation and post-irradiation due to gamma shows a decrease of optical transmittance up to 55% and 70% at 200 kGy. A decrease in band gap was also tabulated from the transmittance and shows a decrease from 3.85 eV to 3.62 eV for CuGaO2 and 3.50 eV to 3.28 eV for ZnO after exposure towards gamma irradiation. However, exposure towards neutron flux of 6.5x1015 n/cm2 only shows small significant changes with transmittance increasing to 85% and 80% for p-CuGaO2 and n-ZnO, with a band gap of 3.84 eV and 3.50 eV.As the samples were irradiated with gamma ray, the high energy particle loses its energy in small steps through the interaction with electrons in the materials causing nuclear Collison. This will then in turn create defects in the material such as the formation of color centers (Farbe center') that absorbs the signal photons which results to the degradation of the light transmission efficiency of the thin film. On the 1-V properties, the decrease in the turn-on voltage of the diode varies with increasing radiation dose for both gamma and neutron flux exposure. The maximum, turn-on-voltage of the prepared diode was shown to be 1.5 V. Exposure towards gamma, shows that the turn-on-voltage has a higher turn-on-voltage of 4.7 v at 200 kGy. However, the effect of neutron flux at 6.Sx1015 n/cm2 shows a small significant difference of 1.7 V. Results shows moderate mitigation towards irradiation, indicating that n-ZnO/p-CuGa02 thin film is capable of withstanding harsh radiation environment while still retaining its semiconductor as the changes in band gap ranges between 3 eV to 4 eV after post-irradiation |
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