| Summary: | 博士 === 國立交通大學 === 電子物理系 === 90 === (AlxGa1-x)0.5In0.5P quaternary alloys, lattice matched to GaAs substrates, have been widely employed in space solar cells, visible wavelength laser diodes (LDs) and high-efficiency light-emitting diodes (LEDs). As the Al composition increases from 0 to 0.5, the direct bandgap (Γ) energy of the (AlxGa1-x)0.5In0.5P layer increases from 1.9eV to 2.26eV, which covers the red to yellow-green portion of visible spectrum. As generally known, deep levels in opto-electronic devices significantly reduce the efficiency. Therefore, investigation on the deep levels in AlGaInP materials is important. First, two majority carrier traps, N1 and N2, were observed in Te-doped AlGaInP alloys with activation energies of 0.165 and 0.385 eV, respectively. Both the trap concentrations were observed to be increased with elevating the Te concentration, indicating these traps as dopant-related defects. Furthermore, both dopant-related defects showed strong correlation with Al composition in AlGaInP alloys, both of which reached the maximum concentrations at around x=0.5. On the other hand, the deep levels in p-type AlGaInP alloys have also been studied, but there was no defects observed in Mg-doped AlGaInP by deep level transient spectroscopy measurement. Various V/III mole ratios were used for growing DLTS samples and a phosphorous vacancy related trap, P2, was found in the Te-doped AlInP when the V/III mole ratio is below 120. Meanwhile, the P2 concentration obviously increased with decreasing V/III mole ratio. This defect was an electron trap, with the activation energy of 0.65. Thermal-induced defects in AlInP have also been studied by annealing the samples at 400, 500, 600 and 700 ℃ for 30 mins under N2 ambient. The sample structure herein was Schottky diode due to its simple for analyzing the defects. A thermal-treatment-induced deep level, T2, was found in the AlInP layers when the annealing temperature was higher than 500℃. Meanwhile, the T2 concentration obviously increased with elevating the annealing temperature. The emission activation energy, Ea, of trap T2 deduced from the slope of the Arrhenius plot was around 0.57 eV. Both deep electron traps and hole traps created by gamma-ray irradiation in GaInP layers have been extensively studied. Three deep electron traps, GN1 GN2 and GN3, were observed, and verified as a bulk defect and two interface states, while GP1 and GP2, were identified as deep hole traps and verified as a bulk defect and a interface state. The activation energies deduced by Arrhenius plots of bulk traps GN1 and GP1 were around 0.13 and 0.29 eV.
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