Characterization of SiC Implanted with B or Al Using Thermal Admittance Spectroscopy
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Characterization of SiC Implanted with B or Al Using Thermal Admittance Spectroscopy S.R. Smitha, M.A. Capanob, and A.O. Evwarayec Air Force Research Laboratory, Materials and Manufacturing Directorate, AFRL/MLPS 3005 P Street, Wright-Patterson Air Force Base, OH 45433-7707 a
University of Dayton Research Institute, 300 College Park, Dayton, OH 45469-0178 Purdue University, Department of Electrical and Computer Engineering, West Lafayette, IN 47907 c University of Dayton, Physics Department, 300 College Park, Dayton, OH 45469-2314 b
ABSTRACT We have measured the thermal activation energies of electrically active defects in 4Hand 6H-SiC implanted with either Al or B ions, using Thermal Admittance Spectroscopy. The net acceptor concentrations were monitored using room temperature low frequency CapacitanceVoltage measurements. The substrates were n/n+ epilayers. The implantations plus annealing produced p-type layers that were acceptable for characterization. The specimens were annealed in Ar at 1600 º C, after which Ni Schottky diodes were fabricated on the specimens. Annealing times were 5, 15, 30, and 60 min. In some of the specimens, a shallow level was found that did not correspond to known levels . As the annealing progressed, energy shifts were noted for some of the detected levels. In some specimens, the implanted p-type impurity and the n-type residual dopants in the substrate were simultaneously detected. Measurements of electrically active ptype species were compared to “control” specimens implanted with Ar. From this comparison, we conclude that at least one shallow donor level is introduced into the bandgap by the implantation process, and is not annealed out. The defects associated with the implantation may affect actual device performance of diodes by destabilizing the lattice occupation of the implanted dopant atoms (energy shift with annealing), and act as lifetime killers.
INTRODUCTION Ion implantation is generally accepted as the primary means of achieving selective doping in silicon carbide (SiC). This fact has motivated studies of many aspects of SiC ion implantation to gain a better understanding of this process step [1,2]. Much of the published literature regarding implantation into SiC deals with dopant activation [3], or the use of implantation within the context of device performance [4]. While these aspects are fundamental to the fabrication of SiC devices, other aspects of SiC implantation are important from either a scientific or a technical perspective. Two examples relate to the nature of electrically active defects and to the damage characteristics following ion bombardment and thermal annealing. Electrically active defects of SiC materials are of interest because they may significantly influence transport characteristics within the implanted semiconductor. Residual damage is an important parameter to investigate for many reasons. One strong reason is to grasp how irradiation-induced extended defects affect processing temperatures needed to achieve a specific ratio of dopant activatio
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