Diamond Schottky barrier diodes

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

Diamond semiconductor technology for RF device applications

This paper presents a comprehensive review of diamond electronics from the RF perspective. Our aim was to find and present the potential, limitations and current status of diamond semiconductor devices as well as to investigate its suitability for RF device applications. While doing this, we briefly analysed the physics and chemistry of CVD diamond process for a better understanding of the reasons for the technological challenges of diamond material. This leads to Figure of Merit definitions which forms the basis for a technology choice in an RF device/system (such as transceiver or receiver) structure. Based on our literature survey, we concluded that, despite the technological challenges and few mentioned examples, diamond can seriously be considered as a base material for RF electronics, especially RF power circuits, where the important parameters are high speed, high power density, efficient thermal management and low signal loss in high power/frequencies. Simulation and experimental results are highly regarded for the surface acoustic wave (SAW) and field emission (FE) devices which already occupies space in the RF market and are likely to replace their conventional counterparts. Field effect transistors (FETs) are the most promising active devices and extremely high power densities are extracted (up to 30 W/mm). By the surface channel FET approach 81 GHz operation is developed. Bipolar devices are also promising if the deep doping problem can be solved for operation at room temperature. Pressure, thermal, chemical and acceleration sensors have already been demonstrated using micromachining/MEMS approach, but need more experimental results to better exploit thermal, physical/chemical and electronic properties of diamond

Silicon carbide, a semiconductor for space power electronics

After many years of promise as a high temperature semiconductor, silicon carbide (SiC) is finally emerging as a useful electronic material. Recent significant progress that has led to this emergence has been in the areas of crystal growth and device fabrication technology. High quality single-crystal SiC wafers, up to 25 mm in diameter, can now be produced routinely from boules grown by a high temperature (2700 K) sublimation process. Device fabrication processes, including chemical vapor deposition (CVD), in situ doping during CVD, reactive ion etching, oxidation, metallization, etc. have been used to fabricate p-n junction diodes and MOSFETs. The diode was operated to 870 K and the MOSFET to 770 K

Silicon carbide, a high temperature semiconductor

Electronic applications are described that would benefit from the availability of high temperature semiconductor devices. Potential materials for these devices are compared and the problems of each are discussed. Recent progress in developing silicon carbide as a high temperature semiconductor is described