| dc.description.abstract | ABSTRACT
In this dissertation we investigated the performances of metal- semiconductor contacts in different materials and their applications for optoelectronic devices.
For the study of thin Pt film deposited on p-Si substrate, which usually formed PtSi film as a kind of silicide, it can be used to fabricate the Schottky Barrier Diode (SBD) and performed as infrared focal plane array sensors used widely in the detection wavelength range of 3~5 mm. The electrical Schottky barrier height of 0.186 eV was obtained. It was observed that the grain size and the film thickness have negligible effect on the electrical barrier height. However, the quantum efficiency of the SBDs is strongly dependent on the film thickness. The quantum efficiency of the designed Schottky barrier detectors with PtSi film thickness of about 80Å at its peak value exceeded 1%. We concluded the positive quantum efficiency dependence on the film thickness is referred to the enhancement of elastic phonon scattering and the decrease of the quantum efficiency is deduced from the inelastic scattering, like hole/hole scattering, imperfection scattering and impurity scattering during the hot hole transporting to the PtSi/Si interface.
For the study of the InGaP Schottky contact with Ti/Pt/Au metals, thermal reliability and characterization of contacts were investigated. The best Schottky properties with a barrier height of 1.01 eV and ideality factor of 1.24 are obtained from the InGaP Schottky diodes treated with the diluted HCl solution. However, we found that the diluted NH4OH is more suitable chemical solution for the treatment of the InGaP surface in fabrication process. No significant change was found for samples annealed up to 450 ℃ but a drastic degradation was observed in samples annealed at 500℃ in the thermal reliability experiment. We deduce that the degradation was caused by the interdiffusion and penetration of metals into the semiconductor from Auger electron spectroscopy analysis.
Further, the ohmic contact properties of metals contacts with low and high band-gap semiconductor were examined. In the comparison of ohmic performance of Ti/Ni/Au and Ti/Pt/Au on InAs/graded/InGaAs/GaAs layers, good nonalloyed specific contact resistance was 1.0 x 10-6 and 3.0 x 10-6 W cm2 for Ti/Pt/Au and Ti/Ni/Au metallization systems, respectively. However, the thermal stability can be achieved at least up to 350℃ for Ti/Pt/Au metallization system, while the Ti/Ni/Au metallization can only thermally stabilize at 250℃. The degradation of the specific contact resistance at high annealing temperature is attributed to the induced decomposition of InAs and graded InGaAs layers from Rutherford backscattering spectroscopy spectra and the Auger electron spectroscopy depth profile.
For the ohmic contacts study of metal contacts on GaN, ultra-low specific contact resistivity of 9.8 x 10-6 W cm2 and 8 x 10-6 W cm2 were obtained using Nd/Al metallization with CTA of 250℃ for 5 min and RTA of 600℃ for 30 s. Surface morphology was smooth in the temperature range from 550 to 650℃ for rapid thermal annealing observed using atomic force microscopy. From Auger electron spectroscopy depth profiling analysis, the degradation of contact characteristics was due to the oxidation of Nd metal.
Finally we investigate the chemical solution treatment and post-annealing to eliminate the reactive-ion etching damage on GaN surface. By using KOH and H3PO4: H2O chemical solution treatments, the ohmic resistance of GaN LEDs can be improved by the removal of native oxide. Using thermal annealing above 700℃, the reverse breakdown performance of the GaN LEDs can be improved by restoration of the ion-induced damage. Nevertheless, at a temperature higher than 1000℃, both the forward and reverse current-voltage characteristics of the GaN LEDs are degraded because of the decomposition of GaN and the loss of nitrogen. | en_US |