Diamond Schottky barrier diodes

Abstract

Research on wide band gap semiconductors suitable for power electronic devices has spread rapidly in the last decade. The remarkable results exhibited by silicon carbide (SiC) Schottky batTier diodes (SBDs), commercially available since 2001, showed the potential of wide band gap semiconductors for replacing silicon (Si) in the range of medium to high voltage applications, where high frequency operation is required. With superior physical and electrical properties, diamond became a potential competitor to SiC soon after Element Six reported in 2002 the successful synthesis of single crystal plasma deposited diamond with high catTier mobility. This thesis discusses the remarkable properties of diamond and introduces several device structures suitable for power electronics. The calculation of several figures of merit emphasize the advantages of diamond with respect to silicon and other wide band gap semiconductors and clearly identifies the areas where its impact would be most significant. Information regarding the first synthesis of diamond, which took place back in 1954, together with data regarding the modern technological process which leads nowadays to high-quality diamond crystals suitable for electronic devices, are reviewed. Models regarding the incomplete ionization of atomic dopants and the variation of catTier mobility with doping level and temperature have been elaborated and included in numerical simulators. The study introduces the novel diamond M-i-P Schottky diode, a version of power Schottky diode which takes advantage of the extremely high intrinsic hole mobility. The structure overcomes the drawback induced by the high activation energies of acceptor dopants in diamond which yield poor hole concentration at room temperature. The complex shape of the on-state characteristic exhibited by diamond M-i-P Schottky structures is thoroughly investigated by means of experimental results, numerical simulations and theoretical considerations. The fabrication of a ramp oxide termination on a diamond device is for the first time reported in this thesis. Both experimental and simulated results show the potential of this termination structure, previously built on Si and SiC power devices. A comprehensive comparison between the ramp oxide and two other versions of the field plate termination concept, the single step and the three-step structures, has been performed, considering aspects such as electrical performance, occupied area, complexity of technological process and cost. Based on experimental results presented in this study, together with predictions made via simulations and theoretical models, it is concluded that diamond M-i-P Schottky diodes have the ability to deliver significantly higher performance compared to that of SiC SBDs if issues such as material defects, Schottky contact formation and measurement of reliable ionization coefficients are carefully addressed in the near future.