Min Hong Kim

Changes in the growth mode of low temperature GaN buffer layers with nitrogen plasma nitridation of sapphire substrates

Low temperature GaN buffer layers were grown by remote plasma enhanced metalorganic chemical vapor deposition on various pretreated sapphire substrates. The effects of the initial nitridation of sapphire substrates by rf nitrogen plasma on the subsequent growth mode and the crystallinity of the GaN buffer layers were studied. GaN buffer layers on non-nitridated sapphire substrates showed a three-dimensional island growth mode with rough surfaces and misoriented islands. On the other hand, those grown on nitridated sapphire substrates showed an enhanced two-dimensional growth mode with near-equilibrium truncated hexagonal pyramids. The structural quality of the low temperature GaN buffer layer improved significantly with nitrogen plasma nitridation.

HIGHLY (200)-ORIENTED PT FILMS ON SIO2/SI SUBSTRATES BY SEED SELECTION THROUGH AMORPHIZATION AND CONTROLLED GRAIN GROWTH

Highly (200)-oriented Pt films on SiO 2 /Si substrates were successfully prepared by a combination of a dc magnetron sputtering using Ar/O 2 gas mixtures and subsequent controlled annealing. The intensity ratio of (200) to (111) planes ( I 200 / I 111 ) was over 200. The (200)-oriented Pt microcrystallites were less susceptible to amorphization due to their lower strain energy with oxygen incorporation than (111)-oriented ones. The controlled grain growth from the selected (200)-oriented seed microcrystallites during subsequent annealing provided a kinetic pathway where grain growth of the seed microcrystallites was predominant, while suppressing the nucleation of surface energy-driven, (111)-oriented seed microcrystallites and subsequent (111) preferred orientation.

Effects of hydrogen on carbon incorporation in GaN grown by remote plasma-enhanced metal-organic chemical vapor deposition

The effects of hydrogen on carbon incorporation in GaN layers grown by remote plasma-enhanced metal-organic chemical vapor deposition were investigated. Gas-phase decomposition of TEGa was enhanced at high RF power and reactor pressure conditions. With increase in hydrogen fractions in the downstream plasma, optical emission intensity of CN abruptly decreased. It is suggested that active hydrogen species may scavenge the carbon-containing species in the gas phase, resulting in reduced carbon incorporation in GaN layers measured by 10 K photoluminescence and secondary-ion mass spectroscopy.

Characterization of Platinum films Deposited by a Two-Step Magnetron Sputtering on SiO2/Si Substrates

In this study, defect-free Pt films with good adhesion were deposited on SiO 2 /Si substrates by a two-step magnetron sputtering. This method consists of the first sputtering step using Ar/O 2 gas mixture and the second step using Ar. After two-step deposition, an annealing process was followed at 600-1,000 °C in ambient atmosphere. In the first step, oxygen containing Pt films were deposited. Oxygen incorporated in the Pt films completely diffused out during the high temperature annealing. After the annealing process, the film became dense without catastrophic failures such as hillock, pinhole or buckling. Adhesion strength of films produced by this process was good enough to pass a tape test. It is believed that the good adhesion and the observed microstructural evolution are related to the oxygen in Pt films introduced during the first sputtering step. Adhesion, microstructural evolution and the role of oxygen in Pt films are briefly discussed.

Stress of Platinum Thin Films Deposited by Dc Magnetron Sputtering Using Argon/Oxygen Gas Mixture

Pt thin films were deposited by a DC magnetron sputtering with Ar/O 2 gas mixtures. Due to the oxygen incorporation into the Pt films, deposition rate and resistivity of as-deposited Pt thin films increased with oxygen fraction in the sputtering gas. No peaks from crystalline Pt oxides were observed by x-ray diffraction (XRD) and excessive oxygen incorporation into Pt lead to an amorphous Pt oxide formation. More oxygen could be incorporated in the Pt thin films deposited at lower temperatures and at higher total pressures. Incorporated oxygen was completely removed after an annealing at 800 °C for an hour in air ambient, as the resistivity of the Pt thin films recovered their bulk resistivity values. Tensile stress of the Pt films decreased with oxygen incorporation, and approached a saturation level at high resistivity of the films, presumably due to the formation of amorphous Pt oxides.