Numerical and Experimental Characterization of 4H-SiC Schottky Diodes ISDRS 2003 Xiaohu Zhang, N.Goldsman, J.B.Bernstein, J.M.McGarrity and S. Powell Dept. of Electrical and Computer Engineering University of Maryland, College Park, MD 20742 Xiaohu@email@example.com
Introduction • 4H-SiC appears to be the structure that seems especially promising for the development of Schottky Diodes: • Wide bandgap (3.26eV) • High critical electric field (2.2×106V) • Thermal conductivity (3.2-3.8W/cm·K) • Saturated electron drift velocity (2.0×107cm/sec).
Introduction • A methodology was developed to extract key physical parameters for 4H-SiC Schottky diode operation including: • Temperature dependent mobility • Mobility versus position and doping • Schottky barrier height versus temperature • Device performance dependence on geometry and • doping
Methodology • Combined simulation and experimental methods to extract the key parameters. • Simulations were achieved by developing a drift-diffusion based CAD tool tailored for SiC Schottky diode analysis • Experiments involved measuring current-voltage characteristics under different controlled external temperatures. • Coordinated use of simulation and experiment facilitated the parameter extractions.
Schottky contact Metal Epitaxial n Drift Layer Epitaxial n+ Layer Device Structure The schematic cross section of the Simulated SiC Schottky diode
Simulation and Physical Models A.Drift-diffusion model B. Intrinsic Carriers and Band Gap Narrowing C. Mobility Modeling
Results The experiment (dot curve) and simulation results (solid curve) of the forward current-voltage (IV) characteristics of the Ti/4H-SiC Schottky diode under four different temperatures show a very good agreement.
Results The simulation result shows a much more accurate result than the analytical analysis
Mobility A T-2.4 variation of 4H-SiC mobility was obtained. Mobility variation from n+ epilayer to n- drift epilayer under different temperature Average mobility for different doping density under different temperature
Barrier Height Simulation results indicate that the barrier height displays negative temperature dependence.
Device improvement Better IV characteristic of 4H-SiC Schottky diodes can be shown in this simulation program by changing the length and doping density in two epilayers. It shows clearly that the current can be increased more than five times by changing the length of the n-drift epilayer from 4µm to 1µm
Device improvement The doping density of n-epilayer changing from 1×1015 cm-3 to 1×1018 cm-3 The doping density of n+ epilayer Changing from 1×1015 cm-3to 1×1018 cm-3
Summary and Conclusion • High temperature4H-SiC Schottky Barrier Diode measurements were performed • A 4H-SiC Schottky diode device simulator was developed • Simulations and experiments were performed in conjunction to extract key diode parameters. • Results show mobility values ranging from 1000 to 200cm2/Vsec temperatures ranging from 273 to 573K for doping of 1015/cm3
Summary and Conclusion • Results show mobility values ranging from 250 to 50cm2/Vsec temperatures ranging from 273 to 573K for doping of 1018/cm3 • Schottky barrier height ranged from 1.14 to 0.91eV for temperatures ranging from 298 to 423K • Shorter drift regions give rise to larger diode forward currents.