Development of Diamond Schottky Barrier Diode

Diamond, which has excellent physical properties, is attractive for use in industrial applications. Because diamond is rated the highest for hardness and heat conductivity among all known materials, it is widely used for products such as abrasive grains, cutting tools, and heatsinks. Diamond also exhibits excellent transparency even in the ultraviolet range and can be applied to optical tools. Because diamond is composed of carbon atoms, it has a high biological affinity and is used in dental drills and surgical knives. Since carbon is a group element in the periodic table just like Si and Ge, diamond can be used as a semiconductor. SiC and GaN that are recently being studied extensively as wide band-gap semiconductors have band gaps of 3.1 eV and 3.5 eV, respectively, while diamond has a wider band gap of 5.5 eV. Various figures-of-merit (FOM) have been proposed by E. O. Johnson,(1) B. J. Baliga(2) and A. Q. Huang(3) as evaluation indices of power device materials defined based on physical properties such as carrier mobility, breakdown voltage and thermal conductivity. In the case of Baliga’s FOM, the values for Si and SiC are 1 and 630, respectively, while that for diamond is as high as 44000, which means that diamond is a much more suitable material for high power devices than conventional semiconductor materials. As the technologies for growing and doping diamond substrates have been increasingly developed in recent years, many researchers developed diamond electronic devices. Since the earlier study of diamond Schottky barrier diode (SBD) by H. Shiomi et al.(4) (Sumitomo Electric Industries, Ltd.), diamond SBD has been developed by D. J. Twitchen(5), T. Teraji(6), and S. J. Rashid (7). After the success in n-type diamond doping, S. Koizumi et al.(8) had succeeded in developing a pn diode. The research groups led by H. Kawarada(8) and M. Kasu(10) developed the diamond MISFET and MES respectively using non-doped, hydrogen terminated diamond and achieved a cut-off frequency as high as 28 GHz. These devices were developed as high–frequency, high-power telecommunication devices. On the other hand, the National Institute of Advanced Industrial Science and Technology (AIST) has begun its research on diamond high power switching devices since 2004. In 2005, Sumitomo Electric started a collaborative research on diamond SBD with AIST. Because the SBD structure is the most simple structure among various power devices, Sumitomo Electric selected SBD as the most suitable device in terms of providing feedback to the diamond crystallinity evaluation process. In this paper, the authors explain about the diamond SBD developed in the collaborative research and also about the possibility of developing a device featuring both energy saving and high power density .