Deep Level Defects in He-implanted n-6H-SiC Studied by Deep Level Transient Spectroscopy
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Deep Level Defects in He-implanted n-6H-SiC Studied by Deep Level Transient Spectroscopy X. D. Chen, C. C. Ling,* S. Fung, C. D. Beling, and H. S. Wu Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. China G. Brauer, W. Anwand, and W. Skorupa Institut für Ionenstrahlphysik und Materialforschung, Forschungszentrum Rossendorf, Postfach 510119, D-01314 Dresden, Germany ABSTRACT Deep level transient spectroscopy (DLTS) was used to study deep level defects in He-implanted n-type 6H-SiC samples. Low dose He-implantation (fluence ~2×1011 ions/cm2) has been employed to keep the as-implanted sample conductive so that studying the introduction and the thermal evolution of the defects becomes feasible. A strong broad DLTS peak at 275K-375K (called signal B) and another deep level at EC-0.50eV were observed in the as-implanted sample. The intensity of the peak B was observed to linearly proportional to the logarithm of the filling pulse width, which is a signature for electron capture into a defect related to dislocation. After annealing at 500oC, the intensity of peak was significantly reduced and the remained signal has properties identical to the well known Z1/Z2 deep defects, although it is uncertain whether the Z1/Z2 exist in the as-implanted sample or it is the annealing product of the dislocation-related defect. The E1/E2 defect (EC-0.3/0.4eV) was not presence in the as-implanted sample, but was observed after the 300oC annealing. INTRODUCTION Silicon carbide (SiC) is a wide band-gap semiconductor material having unique physical and electronic properties for fabricating high-temperature, high-power, and high-frequency electronic devices [1]. Ion-implantation is an important technique for the selective doping of SiC because of the extremely small diffusion constants of the dopant impurities in SiC. Defects are usually induced by the ion implantation or the post-implantation annealing processes and some of these defects do not anneal out at very high temperatures [2-4]. Ion implantation or particle irradiation induced deep level defects in SiC have been extensively studied by capacitance transient techniques such as deep level transient spectroscopy (DLTS) [2-11]. Deep levels at EC-0.6/0.7eV (termed Z1/Z2) are generated either by electron irradiation or by ion implantation, and the concentration of these centers is reduced by annealing below 1000oC. Another pair of important deep levels EC-0.3/0.4eV are usually referred to E1/E2 and the concentration of these centers is strongly reduced (the DLTS signal of E1/E2 is below the detection limit) by annealing at 1200-1400oC [2-11]. E1/E2 are the dominant peaks in the DLTS spectra of the as-electron-irradiated 6H-SiC samples [4-8]. For the cases of deuterium implanted [4], He implanted [3,6,9], and neutron irradiated [10] n-type 6H-SiC, E1/E2 are not the peaks having the highest intensities. However their intensities increase with increasing annealing temperature before they start annealing out [3,4,10]. The less prominent peaks labeled
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