Author : Alex Molina
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (133 download)
Book Synopsis Semiconductor Surface Passivation and Metallization for Schottky Diodes by : Alex Molina
Download or read book Semiconductor Surface Passivation and Metallization for Schottky Diodes written by Alex Molina and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Research into gallium nitride (GaN) has borne fruit and holds further promise for the optoelectronics and electronics industries. Among the fields of active research is exploiting GaN for power electronics, with one example being Schottky barriers as power rectifiers. However, one challenge in implementing GaN-based technologies arises from the device processing and choices involved when fabricating metal/semiconductor contacts. Consequently, a study of metallizations to GaN based on thermodynamics with careful selection of the surface treatment and deposition techniques is of the upmost importance. The first objective of this dissertation was to understand the role of HBr in lessening the contaminants on various semiconductor surfaces. Motivated initially a need to passivate Ge nanostructures, HBr vapor was used to remove the native oxide and passivate a Ge wafer, and x-ray photoelectron spectroscopy (XPS) was used to study the surface. For exposures of at least 20 min above the 48% HBr solution, we found a clear reduction in the amount of oxide present. Interestingly, stability against reoxidation in air was greatly improved using longer exposures to HBr vapor, and XPS reveals that bromine is adsorbed onto these surfaces, suggesting that it is physically blocking H2O and O2 molecules from coming into contact and reoxidizing the Ge surface. Given its success as a surface treatment, aqueous HBr was also tested on GaN. The GaN surfaces, examined by XPS, exhibited no noticeable difference in C and O surface contaminants between HBr and HCl, which is widely used for cleaning GaN surfaces. This finding enhanced our confidence in the efficacy of using HCl for surface preparation. The main objective of this dissertation was to choose a pure transition metal, metal alloy, and compound metallization for GaN based on their thermodynamic stability against metallurgical reactions, high work functions, and conductivity. The only pure transition metal in thermodynamic equilibrium with GaN is rhenium (Re). Prior work on Re/n-GaN has demonstrated diodes with good thermal stability, but the diodes were not as high in quality as the ones produced in this dissertation, due in part to improved crystal growth technology as well as improvements in device processing in this dissertation. Re diodes were fabricated to study the effects of deposition, processing, and annealing on the electrical characteristics of the diodes. As-deposited diodes varied dramatically depending on deposition technique. Electron-beam evaporated Re/Au diodes consistently demonstrated low ideality factors (1.02-1.04) and high barrier heights (0.72-0.82 eV), whereas sputtered Re diodes had high ideality factors (1.26-1.73) and low barrier heights (0.38-0.41 eV), likely due to process-induced defects. However, a remarkable improvement was observed in their electrical characteristics when annealed at 500°C for 5 min in which the barrier height improved to 0.74 eV and the ideality factor to 1.02. Compared to baseline palladium (Pd) diodes fabricated on a similar substrate, the Re diodes were more resilient against annealing conditions that degrade their Pd counterparts. Pd diodes consistently showed degradation after a mild thermal excursion (250°C for 2 h) during dielectric deposition, where the barrier height changed from 0.99 eV to 0.92 eV and ideality factor from 1.02 to 1.13. After annealing at 600°C for 5 min (as a direct comparison to Re diodes) the Pd diodes' barrier height changed from 0.92 eV to 0.86 eV and ideality factor changed from 1.13 to 1.56, whereas the Re diodes remained stable. Stacked layers of Ni and Ga were also pursued as a metal gallide metallization given past success of nickel gallide contacts surviving high temperatures better than pure Ni contacts. However, preliminary current-voltage (I-V) characteristics found that our diodes degraded after annealing at 400°C and 600°C, which may be due to the inhomogeneity in Ga deposition, since Ga deposits with an uneven morphology. With some regions containing more Ga than others, Ni may still react in patches. This inhomogeneity across that diode resulted in low barrier heights and high ideality factors. Therefore, it was deemed beneficial to choose another contact to study. MoCxNy diodes deposited via remote plasma atomic layer deposition (PE-ALD) were also investigated as an attractive compound candidate. Not only is MoNx conductive, refractory, and thermally stable on GaN, it has a high work function and exhibits good adhesion to GaN. Films were examined by XPS, grazing incidence x-ray diffraction (GIXRD), and transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS) to determine their composition and structure. TEM reveals an abrupt interface between MoCxNy and n-GaN, and that MoCxNy adopts a cubic phase. Remarkably, XPS also shows a significant amount of carbon within the single cubic phase. It is hypothesized that our single-phase MoC0.3N0.7 film is a cubic NaCl-type structure with a lattice parameter of 0.42 nm that has C and N atoms occupying half of the sites on one sublattice. The incorporation of C in our film, and its occupation in the cubic crystal, could be playing a role in improving the electrical characteristics. The diodes demonstrated high barrier height (0.87 eV) after an anneal at 600°C for 5 min, with an ideality factor of 1.02 by I-V measurements, revealing potential for a thermally stable Schottky diode. The conclusions drawn and experiments developed augment the understanding of device fabrication, metallization, and processing for contacts to n-GaN applications for high-temperature and high-power electronics.
