In this thesis, we grew undoped GaN and Si-doped GaN films on sapphire by metal organic chemical vapor deposition (MOCVD) system. For the purpose to investigate the influences of undoped GaN films, we modulated H2 gas flow rate and nitridation time in the undoped GaN growth conditions. The ramping rate, Si2H6 flow rate and undoped GaN film thickness were varied to study the influences on Si-doped GaN films. When H2 gas flow rate was increased, it led to carbon pollution reduced and improved films quality. Too long or too short nitridation time would change film qulity seriously. In the Si-doped GaN films growth, the films quality become worse when the ramping rate was too quick or too slow. The relationship between the carrier concentration of Si-doped GaN films and Si2H6 flow rate was linear. The electron mobility of Si-doped films will not increase apparently until Si2H6 flow rate up to 7.19nmol/min . Undoped GaN film which was pregrown before Si-doped GaN could improve the crystal quality of Si-doped GaN films, and it will influence the optical properties of Si-doped GaN film, such as PL spectra.

Bochum, Univ., Diss., 2005. / Computerdatei im Fernzugriff.

Bochum, University, Diss., 2005.

In this study, the characteristics of atomic layer deposited TiO2 films on silicon substrate were investigated. The physical and chemical properties were measured and surveyed. And an Al/ALD-TiO2/Si MOS structure was used for the electrical characterizations. For the electrical property improvements, we investigated the atomic layer deposited TiO2 films by the post-anneal treatments in nitrogen and oxygen ambient. Furthermore, the TiO2 films were passivated by fluorine ions to decrease the leakage current density that came from the liquid phase deposited SiO2 stacks. After the post-annealing and fluorine ions passivation treatments, the dielectric constant of atomic layer deposited TiO2 film was maintained and the leakage current density was improved.

Self-organized GaN nanostructures have been accomplished with lattice-(mis)matched using MOCVD. A lattice mismatched system (i.e. GaN nanostructure/ AlN) was utilized with S-K mode mechanism, whereas, metallic droplet method (i.e. Vapor-Liquid-Solid method) was employed in the lattice matched system (i.e. GaN nanostructure / AlGaN). The nanostructure size is adjustable by changing growth parameters (height: 2 ~ 15nm and diameter: 10 ~ 100nm). It has been found that the photon emission energy is tunable relative to the nanostructure size, and smaller nanostructures have larger photon energy. However, a numerical modeling was performed to investigate the relationship between quantum confinement (and/or piezoelectric polarization) and the dot size. For dot height < 4.1nm, the confinement effect is larger than the piezoelectric effect, otherwise the piezoelectric effect is more dominant. In addition, GaN nanostructures grown on Al0.15Ga0.85N have smaller lattice mismatch (less than 0.5%) than the GaN nanostructures grown on AlN. Therefore, the quantum confinement in a GaN/Al0.15Ga0.85N system is more dominant in determining photon emission energy than in a GaN/AlN system. The nanostructure advantages of quantum confinement and high thermal stability have been studied for the achievement of room temperature ferromagnetism using TM (transition metal; Mn or Fe). The transition metal (Mn or Fe) enhances nucleation of islands, resulting in size and density improvements. The magnetization measurements revealed magnetic properties of ferromagnetic nanostructure. Especially, room temperature ferromagnetism was observed in GaFeN nanostructures, which can contribute to ferromagnetic semiconductors operating above room temperature.

As the electronic device scale down, replacing conventional SiO2 with high dielectric constant material is very important. Due to its have high dielectric constant (£`// = 170, £`¡æ = 90), high refractive index (~2.5) and high chemical stability. TiO2 is a promising candidate for fabricating thin dielectrics in dynamic random access memory (DRAM) storage capacitors and as gate dielectrics of metal-oxide-semiconductor field effect transistor (MOSFET) without the problem of conventional SiO2 thickness scaling down in ULSI processes because of its high dielectric constant. TiO2 thin films deposited on p-type (100) Si substrate were investigated by a cold wall horizontal MOCVD system using Ti(i-OC3H7)4, N2O as precursors in the deposition temperature range from 400 ¢J to 650 ¢J. XRD results indicate that the structures of TiO2 films are polycrystalline and mixture of anatase and rutile phases coexist in the film at the deposition temperature of 650 ¢J. Electrical properties are strongly influenced by deposition temperature. The electrical properties of as-deposited TiO2 films can be improved by annealing treatment. The TiO2 film at the deposition temperature of 650 ¢J has the highest dielectric constant of 100.3 and at the deposition temperature of 550 oC has the lowest leakage current density of 2.07¡Ñ10-7 A/cm2 under the applied electric field of 5 MV/cm after annealing for 20 minutes at 750 ¢J in O2 ambient. In order to obtain the better electrical properties of TiO2 films on Si substrate, LPD-SiO2 thin films were deposited on the polycrystalline MOCVD-TiO2 films. The minimum equivalent oxide thickness of LPD-SiO2/post-annealed TiO2 film is 51.13

The materials based on GaN have successfully developed on short-wavelength laser diodes (LDs), light-emitting diodes (LEDs) and ultraviolet photodetector. In this study, GaN epitaxial layers have been successfully grown on sapphire substrates. We used several methods including the growth temperature and time of amorphous nucleation layer before growing epilayer and the growth temperature of GaN epilayer to study it. From the results of the photoluminescence (PL) measured at 77K, the X-Ray diffraction measurement, SEM cross sectional views to realize the characteristic and we get a better qualities of GaN epilayers after using the foregoing methods. In this study, the re-crystallization of the amorphous nucleation layer would occur while temperature re-rise to high temperature, and the phenomenon have different crystallinity under the different growth conditions of nucleation layer, which influence the quality and morphology of GaN epilayers seriously. According to the results of the experiments, we study the mechanisms of yellows luminescence and donor-acceptor pair.

Using a numerical method to simulate the Metal-Organic Chemical Vapor Deposition (MOCVD). A study of the GaN films were growth on sapphire substrates, and a new design method which The position of carrier gas inlets and outlets, the gas in inlets by a showerhead reactor, the modified susceptor. The purpose of this research is to maintain deposited GaN film thickness variation range by controlling those parameters which may affect the deposition.

Scaling down of DRAM¡¦s dimensions is a continuous trend since its inception. Therefore, the high dielectric constant material is necessary because the application of conventional SiO2 will reach its physical limits. Due to TiO2 have high dielectric constant (£`// = 170, £`¡æ = 90), high refractive index (~2.5) and high chemical stability, it is a promising candidate for fabricating thin dielectrics in DRAM storage capacitors and as gate dielectrics of MOSFET without the problem of conventional SiO2 thickness scaling down in ULSI processes. TiO2 thin films grown on p-type (100) Si substrate are investigated by a cold wall horizontal MOCVD system using Ti(i-OC3H7)4, N2O as precursors at the growth temperature which ranges from 400 oC to 650 oC. The dielectric constant of poly-crystalline titanium oxide (TiO2) films grown on silicon (Si) by metal organic chemical vapor deposition (MOCVD) is high. The leakage current is also high, which is dominated by the film defect and the grain boundary. The electrical characteristics are also strongly associated with growth temperature. After oxygen annealing, the leakage current is improved due to the reduction of the oxygen vacancy of TiO2 film. However, the electrical characteristics can be further improved by the postmetallization annealing treatment especially under the negative electric field. Post-metallization annealing (PMA) is an effective method in MOS technology to reduce the effective charge density and the interface state density. The mechanism of PMA is to use the reaction between the aluminum contact and hydroxyl groups existed on oxide surface to form active hydrogen and diffuse through the oxide to passivate the oxide traps. Therefore, MOCVD-TiO2/Si films which treated by O2-annealing and PMA with high dielectric constant and low leakage current can be obtained. The leakage current can reach 3.44¡Ñ10^-6 A/cm2 under a negative electric field of 5 MV/cm. The hysteresis loop shift voltage and the interface state densities are 5 mV and 1.17 ¡Ñ 10^11 cm−2 eV^−1, respectively.

The dielectric constant of poly-crystalline titanium oxide (TiO2) films grown on silicon (Si) by metal organic chemical vapor deposition (MOCVD) is high. The leakage current is also high, which is dominated by the grain boundary and lower barrier height. Silicon oxide (SiO2) film is used as an interfacial layer for the structure of MOCVD-TiO2/SiO2/Si. The leakage current is much improved due to the high quality and high barrier height of SiO2/Si, but the total capacitance is lost due to the series of low-dielectric constant SiO2 films and amorphous low dielectric constant of TiO2 film grown on SiO2. Liquid-phase-deposited SiO2 is used as a cap layer for the structure of LPD-SiO2/MOCVD-TiO2/Si, the high dielectric constant of MOCVD-TiO2/Si is preserved. The leakage current is much improved due to the high barrier height SiO2 and the passivation of the dangling bonds of the grain boundary of poly-crystalline MOCVD-TiO2 films by the F from LPD-SiO2 films. Therefore, high dielectric constant and low leakage current LPD-SiO2/MOCVD-TiO2/Si films were obtained. Therefore, MOSFET with LPD-SiO2/MOCVD-TiO2 gate oxide can have lower off state leakage current, smaller subthreshold swing, higher transconductance, and higher field effect mobility. On the other hand, LPD-SiO2/MOCVD-TiO2 film on (NH4)2Sx-treated InP not only can lower leakage current but can lower interface state density. The leakage current densities are 1.37¡Ñ10-7 A/cm2 and 1.45¡Ñ10-7A/cm2 under positive and negative electric fields at 1.5 MV/cm, respectively. The lowest interface state density is 4.7¡Ñ1011 cm-2eV-1 in the band gap. Moreover, the dielectric constant can reach 61.2. Therefore, LPD-SiO2/MOCVD-TiO2 structure is a high dielectric constant and low leakage current film.