Pulsed breakdown of 4 H -SiC Schottky diodes terminated with a boron-implanted p-n junction
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Pulsed Breakdown of 4H-SiC Schottky Diodes Terminated with a Boron-Implanted p–n Junction P. A. Ivanov^, I. V. Grekhov, A. S. Potapov, and T. P. Samsonova Ioffe Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia ^e-mail: [email protected] Submitted November 12, 2007; accepted for publication November 26, 2007
Abstract—Pulsed reverse current–voltage characteristics have been measured in the breakdown region for 1-kV 4H-SiC Schottky diodes terminated with a boron-implanted p–n junction. It was shown that the dynamic breakdown voltage of the diodes increases as the pulses become shorter. Owing to the homogeneous avalanche formation at the edge of the guard p–n junction and to the high differential resistance in the breakdown region, the diodes sustain without degradation a pulsed reverse voltage substantially exceeding the static breakdown threshold. Characteristic features of the pulsed breakdown are considered in relation to the specific properties of the boron-implanted guard p–n junction. PACS numbers: 73.30.+y, 73.40.Cg, 73.40.Lq, 85.30.Kk DOI: 10.1134/S1063782608070178
1. INTRODUCTION The formation of guard rings for 4H-SiC Schottky diodes by boron implantation has been examined previously [1–5]. In particular, we studied in [5] 4H-SiC diodes in which the maximum static reverse voltage of ~910 V is limited by the quasi-uniform avalanche breakdown of the planar p–n junction in its cylindrical edge part (Fig. 1). In this paper, we report the results of further studies of the breakdown in these 4H-SiC Schottky diodes. In particular, dynamic current–voltage (I–V) characteristics were first measured in the breakdown mode with microsecond pulses of varied width. It was found that the dynamic breakdown voltage noticeably increases as the pulses become shorter. In addition, the diodes demonstrated a good stability against reverse pulsed overloading: they sustained voltages of at least 1600 V, which exceeds the static breakdown threshold by nearly a factor of 2. The observed characteristic features of the pulsed breakdown are qualitatively explained in terms of the specific properties of the boron-implanted p–n junction in 4H-SiC.
found in [5] from the results of capacitance–voltage measurements, was ~1.7 µm. Pulsed measurements were performed using the circuit shown in Fig. 2b. The circuit operates as follows.
2. EXPERIMENTAL The diodes under study (Fig. 2a) were fabricated on the basis of commercial epitaxial n–n+ 4H-SiC structures: the donor concentration in the base n-layer was ND = (2–3) × 1015 cm–3 at the thickness of this layer d = 12–13 µm. The diode fabrication technology was described in detail in [5]. The total dose of introduced boron atoms in the p-type region of the guard p–n junction was 9 × 1013 cm–2. The degree of electrical activation of the acceptors introduced can be estimated at ~5%. The depth at which the guard p–n junction lies, 858
200 µA/div 100 V/div
(‡)
EL (b) Fig. 1. (a) I–V characteristic of a 4H-SiC Schottky diod
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