Al + implanted vertical 4H-SiC p-i-n diodes: experimental and simulated forward current-voltage characteristics
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Al+ implanted vertical 4H-SiC p-i-n diodes: experimental and simulated forward current-voltage characteristics Roberta Nipoti1, Giovanna Sozzi2, Maurizio Puzzanghera2, Roberto Menozzi2 1
CNR-IMM of Bologna, via Gobetti 101, I-4038 Bologna, Italy
2
University of Parma, Dipartimento di Ingegneria dell'Informazione, Parco Area della Scienza 181/A, I-43124 Parma, Italy.
ABSTRACT The temperature dependence of the forward and reverse current voltage characteristics of circular Al+ implanted 4H-SiC p-i-n vertical diodes of various diameters, post implantation annealed at 1950 °C/5 min, have been used to obtain the thermal activation energies of the defects responsible of the generation and the recombination currents, as well as the area and the periphery current component of the current voltage characteristics. The former have values compatible with those of the traps associated to the carbon vacancy defect in 4H-SiC. The hypothesis that only these traps may justify the trend of the current voltage characteristics of the studied diodes has been tested by simulations in a Synopsys Sentaurus TCAD suite. INTRODUCTION Recently it has been shown that in epitaxial n-type 4H-SiC during very high temperature treatments (similar to those necessary for the post implantation annealing of SiC) the stationary carbon vacancy concentration (Vc) increases with the treatment temperature [1] and Vc can reach values in the decade 1014 cm-3 that are few orders of magnitudes above those in as grown low doped n-type 4H-SiC. The traps associated to the Vc defect in 4H-SiC are the Z1 and Z2 acceptors with negative-U properties, i.e. single and double acceptors [2], and the EH7 single donor. Z1 is positioned at (0.52-0.67) eV and Z2 at (0.45-0.71) eV with respect to the conduction band (CB), the double acceptor state (2-/0) laying below the single one (-/0) [2]. EH7 is positioned at 1.55 eV from CB [2]. The Z1/2 (2-/0) trap is recognized as carrier life-time killer in 4H-SiC [3]. This work is a preliminary study aimed to test the hypothesis that only the Z1(-/0), Z2(-/0), Z1/2(2-/0) and EH7 (0/+) traps may account for the main features of the measured forward current voltage (I-V) characteristics of Al+ implanted 4H-SiC p-i-n vertical diodes, post implantation annealed at 1950°C for 5min. 1950°C is the temperature showing the maximum Vc formation in 4H-SiC[1]. Such hypothesis has been tested through the simulation of the measured I-V characteristics in the Synopsys Sentaurus TCAD suite [4]. EXPERIMENTAL Vertical p-i-n diodes have been fabricated on n-type, 8° off-axis , homo epitaxial 4H-SiC wafers [5]. The n- epitaxial drift layer is 25 Pm thick with a net donor density of 3×1015 cm-3. The bulk wafer is 350 Pm thick with 0.2 Ωcm resistivity. Circular anodes of
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diameter in the 150-1000 Pm range, have been fabri
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