Isochronal annealing on n-type 4H-SiC epitaxial schottky barriers and investigation of defect levels by deep level transient spectroscopy

Abstract

Schottky barriers were fabricated on 50 μm thick n-type 4H-SiC epitaxial layers. The effective doping concentration was calculated from high frequency (1 MHz) capacitance-voltage (C-V) measurements and was found to be ~ 9×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . Using a thermionic emission model, an effective barrier height of 1.22 eV and an ideality factor of 1.6 were calculated from the room temperature forward current-voltage (I-V) characteristics. The barrier height was also calculated from the C-V measurements and was found to be slightly higher compared to that obtained from I-V measurements, which suggests a spatial variation of surface barrier height across the device surface area. Capacitance mode deep level transient spectroscopy (DLTS) in the temperature range 80 to 800 K revealed the presence of four electron traps located in the energy range of 0.17 - 1.6 eV below the conduction band edge (E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ). Three deep level defects at E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> -0.67 eV (Z×), E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> -1.04 eV (EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> ), and E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> -1.67 eV (EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6/7</sub> ) are detected along with one shallow level defects at Ec-0.17 eV (Ti(c)). The capture cross-sections and defect densities were studied systematically through DLTS measurements before and after isochronal annealing in the temperature range of 100 - 800 K. Among different defects, Z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">½</sub> and EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6/7</sub> are found to be very stable in the entire isochronal annealing range. The defects' parameters are evaluated and correlated with previous studies.