Diamond Schottky barrier diodes

• Main Author: Brezeanu, Mihai
• Published: University of Cambridge 2008
• Subjects: 621.3
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.541832

Research on wide band gap semiconductors suitable for power electronicdevices has spread rapidly in the last decade. The remarkable results exhibited bysilicon carbide (SiC) Schottky batTier diodes (SBDs), commercially available since2001, showed the potential of wide band gap semiconductors for replacing silicon (Si)in the range of medium to high voltage applications, where high frequency operationis required. With superior physical and electrical properties, diamond became apotential competitor to SiC soon after Element Six reported in 2002 the successfulsynthesis of single crystal plasma deposited diamond with high catTier mobility. This thesis discusses the remarkable properties of diamond and introducesseveral device structures suitable for power electronics. The calculation of severalfigures of merit emphasize the advantages of diamond with respect to silicon andother wide band gap semiconductors and clearly identifies the areas where its impactwould be most significant. Information regarding the first synthesis of diamond,which took place back in 1954, together with data regarding the modern technologicalprocess which leads nowadays to high-quality diamond crystals suitable for electronicdevices, are reviewed. Models regarding the incomplete ionization of atomic dopantsand the variation of catTier mobility with doping level and temperature have beenelaborated and included in numerical simulators. The study introduces the novel diamond M-i-P Schottky diode, a version ofpower Schottky diode which takes advantage of the extremely high intrinsic holemobility. The structure overcomes the drawback induced by the high activationenergies of acceptor dopants in diamond which yield poor hole concentration at roomtemperature. The complex shape of the on-state characteristic exhibited by diamondM-i-P Schottky structures is thoroughly investigated by means of experimentalresults, numerical simulations and theoretical considerations. The fabrication of a ramp oxide termination on a diamond device is for thefirst time reported in this thesis. Both experimental and simulated results show thepotential of this termination structure, previously built on Si and SiC power devices. A comprehensive comparison between the ramp oxide and two other versions of thefield plate termination concept, the single step and the three-step structures, has beenperformed, considering aspects such as electrical performance, occupied area,complexity of technological process and cost. Based on experimental results presented in this study, together withpredictions made via simulations and theoretical models, it is concluded that diamondM-i-P Schottky diodes have the ability to deliver significantly higher performancecompared to that of SiC SBDs if issues such as material defects, Schottky contactformation and measurement of reliable ionization coefficients are carefully addressedin the near future.