Silicon vacancy related defect in 4H and 6H SiC E. So ¨ rman, N. T. Son, W. M. Chen, O. Kordina, C. Hallin, and E. Janze ´ n Department of Physics and Measurement Technology, Linko ¨ping University, S-581 83 Linko ¨ping, Sweden Received 18 August 1999 We report on an irradiation-induced photoluminescence PL band in 4H and 6H SiC and the corresponding optically detected magnetic resonance ODMR signals from this band. The deep PL band has the same number of no-phonon lines as there are inequivalent sites in the respective polytype. These lines are at 1352 and 1438 meV in the case of 4H and at 1366, 1398, and 1433 meV in the case of 6H. The intensity of the PL lines is reduced after a short anneal at 750 °C. ODMR measurements with above-band-gap excitation show that two spin-triplet ( S =1) states with a weak axial character are detected via each PL line in these bands. One of these two triplet states can be selectively excited with the excitation energy of the corresponding PL line. These triplet signals can therefore be detected separately and only then can the well documented and charac- teristic hyperfine interaction of the silicon vacancy in SiC be resolved. Considering the correlation between the irradiation dose and the signal strength, the well established annealing temperature and the characteristic hyperfine pattern, we suggest that this PL band is related to the isolated silicon vacancy in 4H and 6H SiC. The spin state ( S =1) implies a charge state of the vacancy with an even number of electrons. By combining the knowledge from complementary electron-spin resonance measurements and theoretical calculations we hold the neutral charge state for the strongest candidate. I. INTRODUCTION SiC is a very promising semiconductor for devices that have to work under extreme conditions. Material properties, such as a wide band gap, good thermal conductivity, a rela- tively high mobility, and high breakdown voltage, make it appropriate for many demanding applications. SiC is the classical example of polytypism, i.e., the material can crys- tallize in many different but closely related crystal structures. The unit cells of the 4H and 6H polytypes contains 4 * 2 =8 and 6 * 2 =12 atoms, respectively. The various atomic sites in such large unit cells have different configurations of their neighbors. The nearest neighbors are always tetra- hedally oriented but the next-nearest neighbors can either be in a cubic k or a hexagonal h configuration. In 4H SiC there is one site of each type h and k while in 6H SiC there are one hexagonal and two cubic sites h, k 1 and k 2 . The two cubic sites differ in the third shell of neighbors. This paper will dwell on a primary defect in SiC that in this case has been produced by high-energy particle bom- bardment. If the energy of these particles is high enough, the atoms in the lattice can actually be pushed out of their places. The primary defects created in this way are generally vacancies and interstitials, but in a binary compound like SiC also the antisites can be formed. There is a reason why a good knowledge about primary defects is especially impor- tant for SiC. The poor diffusivity of dopants in SiC makes ion implantation a more attractive doping method. The bom- bardment of the material with heavy ions creates a lot of defects in the material. In contrast to silicon these primary defects in SiC seem to be stable at room temperature 1–4 and some secondary defects produced during a post-irradiation thermal annealing are stable at least up to 2000 °C, 5 i.e., they are virtually impossible to get rid of. This group of defects are therefore not only of a great scientific but also of great technological interest, since they have to be dealt with in any device process that involves ion implantation. The primary defects are of course also fundamentally in- teresting. At quite an early stage in semiconductor science late 1960s and early 1970s electron-spin resonance ESR measurements revealed some of the fascinating microscopic properties of the vacancy in silicon. Less is still known about the vacancy in diamond, but the properties of the negative charge state has been thoroughly analyzed by ESR. The re- sults from silicon and diamond are in one respect strikingly different. While the different charge states of the vacancy in silicon exhibit a strong lattice relaxation, i.e., a dominating Jahn-Teller effect, the vacancy in diamond has the high-spin ground-state characteristic for a dominating spin-spin inter- action. The extreme relaxation in silicon even results in a reversing of the expected ordering of the different charge states in the band gap. It is therefore not strange that these two fundamental point defects have served as interesting model cases in the development of defect theories. 6 Since SiC in a way is a mixture of the two, it is now interesting if some of the properties of its vacancies can be investigated. Despite all the results reported from investigations of pri- mary defects in SiC by methods like ESR, photolumines- cence PL and deep-level transient spectroscopy DLTS, the knowledge about them is far from as developed as sili- con. Some experimental knowledge about the carbon and silicon vacancy has, however, been gained. In this paper we will mainly refer back to the extensive ESR investigations on 3C, 1,4 6H, 3,4 and 4H Ref. 7 SiC, of what is now accepted to be the ESR signal from the negatively charged silicon va- cancy. The deep PL band, that we here will claim to be related to the silicon vacancy, can be observed from as- grown Lely crystals and was thoroughly investigated already during the 1970s. The characteristics of the band was then reported for the 6H, 8,9 15R, 8,9 and 33R Ref. 10 polytype. Historical remark: It was then usually referred to as the abc band. The most thorough work is the PL study by Hagen PHYSICAL REVIEW B 15 JANUARY 2000-II VOLUME 61, NUMBER 4 PRB 61 0163-1829/2000/614/26138/$15.00 2613 ©2000 The American Physical Society