Papers by Keyword: Carbon Vacancy

Abstract: The carbon vacancy (V_C) is a lifetime-killer defect that hinders the correct functionality of 4H-SiC bipolar devices. Until now, different methods based on carbon interstitial injection, have been proposed, in order to reduce its concentration. However, if on one hand these methods effectively reduce the V_C concentration in the epilayer, on the other they cannot prevent the re-generation of V_C occurring during the manufacture of a p-i-n diode, e.g., p+ implantation and activation. In the following contribution, we employ PIII of B for the formation of the anode for a p-i-n diode. We show that by PIII, it is possible to simultaneously form a p⁺n junction with a low concentration of V_C in the drift layer.

Abstract: Experimental data indicate that carbon vacancies incorporated in active regions of SiC devices are important electrical defects, responsible for device limiting effects such as carrier lifetime reduction. For field-effect transistors that include a 4H-SiC/SiO2 interface, such as at the gate, the oxidation pro- cess is understood to introduce native defects to the SiC, including injection of carbon self-interstitials and vacancies, that diffuse into the active layer and interact with other defects and impurities. It is therefore important to understand the migration behaviour of primary native defects such as VC in the vicinity of 4H-SiC/SiO2 interfaces. We report here the results of a density-functional theory investi- gation into the diffusion of the carbon vacancy in such a region. We conclude that the migration of VC is significantly hindered in the immediate vicinity of the interface, with the energy of diffusion barrier being approximately 15% greater than the corresponding diffusion in bulk 4H-SiC.

Abstract: We electrically characterized 4H-SiC n-type epilayers, oxidized in dry ambient in the 1200<T<1300 °C temperature range, for 75-600 min. Consistently with the literature, our results show the reduction of the concentration of the carbon vacancy concentration and of the D-center. Oxidation times equal or longer than 75 min, lead to the formation of two new electrically active levels in the upper part of the band gap and to four new electrically active levels in the lower part.

Abstract: In recent times, 3C-SiC is gaining more and more interest in terms of applications for optoelectronics and quantum computing. Cubic SiC exhibits a number of luminescent defects in the near infrared originating from deep electronic levels. Temperature dependent photoluminescence measurements were conducted on n-type and p-type 3C-SiC in order to investigate the formation of dopant related point defects as well as intrinsic point defects and defect complexes. The results indicate a number of V_Si, V_C and V_CC_Si related defects which might be suitable candidates for future optoelectronic applications.

Abstract: The diffusion of the carbon vacancy (V_C) in n-type 4H-SiC has been studied using Deep Level Transient Spectroscopy (DLTS). Samples grown along two different crystallographic planes, (0001) or c-cut and (11-20) or a-cut, have been utilized. The samples were implanted with 4.0 MeV C ions to generate V_C’s and subsequently annealed at temperatures between 200 and 1500 °C. Following each annealing stage, concentration versus depth profiles of the V_C were obtained. The V_C is essentially immobile in both the c-cut and a-cut samples up to at least 1200 °C. The 1400 °C annealing stage, however, resulted in considerable migration, predominantly along the a-direction. Using half the difference in the Full Width at Half Maximum (FWHM) of the initial and diffused concentration profiles as a measure of the diffusion length, we deduced the diffusivity of the V_C at 1400 °C to be approximately (3.8±1.1)×10^-14 cm²/s along the c-axis and (4.1±1.2)×10^-13 cm²/s along the a-axis, indicating a substantial anisotropy for the V_C diffusion in 4H-SiC.

Abstract: The carbon vacancy (V_C) is a major limiting-defect of minority carrier lifetime in n-type 4H-SiC epitaxial layers and it is readily formed during high temperature processing. In this study, a kinetics model is put forward to address the thermodynamic equilibration of V_C, elucidating the possible atomistic mechanisms that control the V_C equilibration under C-rich conditions. Frenkel pair generation, injection of carbon interstitials (C_i’s) from the C-rich surface, followed by recombination with V_C’s, and diffusion of V_C’s towards the surface appear to be the major mechanisms involved. The modelling results show a close agreement with experimental deep-level transient spectroscopy (DLTS) depth profiles of V_C after annealing at different temperatures.

Abstract: We present a study of electrically active radiation-induced defects formed in 4H-SiC epitaxial layers following irradiation with fast neutrons, as well as 600 keV H⁺ and 2 MeV He⁺⁺ ion implantations. We also look at electron emission energies and mechanisms of the carbon vacancy in 4H-SiC by means of first-principles modelling. Combining the relative stability of carbon vacancies at different sites with the relative amplitude of the observed Laplace-DLTS peaks, we were able to connect Z₁ and Z₂ to emissions from double negatively charged carbon vacancies located at the h- and k-sites, respectively.

Abstract: We address the key factors limiting charge carrier lifetime in 4H-SiC epilayers by demonstrating a viable method for eliminating carbon vacancy (V_C) related Z_1/2 lifetime killer sites and by introducing a novel approach in depth-resolved characterization of the carrier lifetimes across the epitaxial layer, which allows monitoring the efficacy of the proposed defect reduction scheme also exposing surface and interface recombination effects. We show that a moderate-temperature annealing conducted at 1500 °C for 6 hours under C-rich thermodynamic equilibrium conditions in effect eliminates carbon vacancies in epilayers to the levels below the detection limit (10¹¹ cm^-3) of DLTS measurements. The efficient reduction of V_C-related Z_1/2 sites upon thermal treatment is further proven by a significant increase of the minority carrier lifetime from 0.3µs to 1 µs, the upper limit apparently set by epilayer thickness dependent lifetime. Equally important is the extensive range of defect elimination as evidenced by consistently enhanced lifetime throughout entire 40 μm-thick epilayer, thus suggesting immediate practical implication as a lifetime control method suitable for variable thickness 4H-SiC epilayers.

Abstract: The carbon vacancy (V_C) is a major point defect in high-purity 4H-SiC epitaxial layers limiting the minority charge carrier lifetime. In layers grown by chemical vapor deposition techniques, the V_C concentration is typically in the range of 10¹² cm^-3 and after device processing at temperatures approaching 2000 °C, it can be enhanced by several orders of magnitude. In the present contribution, we show that the cooling rate after high-temperature processing has a profound influence on the resulting V_C concentration where a slow rate promotes elimination of V_C. Further, isochronal annealing of as-grown and as-oxidized epi-layers protected by a carbon-cap was undertaken between 800 °C and 1600 °C. The results reveal that thermodynamic equilibrium of V_C is established rather rapidly at moderate temperatures, reaching a V_C concentration of only a few times 10¹¹ cm^-3 after 40 min at 1500 °C. Hence, the concept of eliminating V_C’s by annealing at moderate temperatures under C-rich equilibrium conditions shows great promise and enables re-annealing of high-temperature processed wafers, in contrast to the procedures commonly used today to eliminate V_C. In-diffusion of carbon interstitials and out-diffusion of V_C’s are discussed as the kinetics processes establishing the thermodynamic equilibrium

Abstract: The carbon vacancy (V_C) is the major charge carrier lifetime limiting-defect in 4H-SiC epitaxial layers and it is readily formed during elevated heat treatments. Here we describe two ways for controlling the V_C concentration in 4H-SiC epi-layer using different annealing procedures. One set of samples was subjected to high temperature processing at 1950 °C for 3 min, but then different cooling rates were applied. A significant reduction of the V_C concentration was demonstrated by the slow cooling rate. In addition, elimination of the V_C’s was also established by annealing a sample, containing high V_C concentration, at 1500 °C for a sufficiently long time. Both procedures clearly demonstrate the need for maintaining thermodynamic equilibrium during cooling.