Single crystals of SiC and their application to blue LEDs

Abstract

Silicon carbide (SIC) has been widely used as an abrasive and fireproof brick because it has mechanical hardness and chemical and thermal stability. Therefore, production processes of polycrystalline SiC, called the Acheson method, were established in 1892 [1]. On the other hand, SiC is also one of the IV-IV compound semiconductor materials, and has a long history of study in the field of semiconductors : Light emission caused by the current injection in SiC was observed in the 1950s for the first time [2]. From the 1960s to the 1970s many groups of researchers in the world focused attention on the potential of SiC and made great efforts to develop SiC material and its applications [3,4,5]. In spite of these great efforts, SiC was not widely applied to semiconductor devices. One of the main reasons why SiC devices were not then commercialized was that no production method of bulky SiC single crystals used for substrates of semiconductor devices had been established. Recently, however, great progress has been made in the fabrication technology of large-size SiC single-crystal ingots [6,7,8] and in epitaxial growth technology [9,10,11,12,13,14,15]. Therefore, optoelectronic and electronic devices using SiC have been produced. SiC has a wide forbidden gap (>~2.2 eV) among the semiconductor materials and both electrical conduction types, i.e., p-type and n-type conduction, of SiC can be easily obtained. Therefore SiC has application potential for light emitting diodes with short wavelength and high-power and high-temperature electronic devices. Crystallographically, silicon and carbon atoms of SiC link with each other due to strong tetrahedral covalent bonds (bond covalency is ~88 %), and SiC has the most closely packed structures in the direction of in cubic type and in c~-SiC. Many varieties of stacking orders of an elemental pair of Si and C layers in the most densely packed direction affords SiC many kinds of periodic structures, i.e., polytypes [16]. Typical SiC polytypes and their properties are tabulated in Table 1. A denotes a pair of silicon and carbon layers in the most densely packed direction, and B and C, which also represent a pair of them, have a position different from A. The