Determination of Surface Recombination Velocity From Current–Voltage Characteristics in SiC p-n Diodes

Surface recombination velocity on mesa sidewalls of SiC p-n diodes with various surface passivation conditions was evaluated from the device-size-dependent preexponential factor of recombination current (J_0rec). The diodes passivated by SiO₂ with postoxidation nitridation were dipped into HF to eliminate a shunt current, which is evoked by the nitrided SiO₂ layer and disturbs the analysis of the recombination current. For accurate determination of the surface recombination velocity, an effective recombination zone width was precisely derived taking account of the distribution of carrier density in the depletion layer. The surface recombination velocity of the diodes without any passivation and with the postoxidation nitridation (NO annealing at 1250 °C for 70 min) was determined as 1.2 × 10⁷ and 6.0 × 10⁵ cm/s, respectively, which indicates that the postoxidation nitridation can reduce the surface recombination by a factor of about 20. We confirmed that TCAD simulation could reproduce the current-voltage characteristics by utilizing the extracted parameters. In addition, an evaluation method was proposed to determine the surface recombination velocity from the high-current region, where diffusion current is dominant.

I. Introduction

Semiconductor devices of 4H-SiC have been intensively investigated for power-electronics applications, which considerably save electrical energy consumption [1]–[4], and the SiC power devices would be more rapidly demanded [5], [6]. SiC unipolar devices, such as MOSFETs and Schottky barrier diodes, have been matured year by year and been practically utilized for medium-voltage (<1.5 kV) applications, substituting Si power devices [7]–[11]. However, it is difficult for the SiC unipolar devices to be applied for higher voltage applications due to a high resistance of the voltage blocking layer. To overcome this issue, SiC bipolar devices, such as p-i-n diodes, bipolar junction transistors (BJTs), and insulated-gate bipolar transistors, have been under investigation, because the bipolar devices can reduce the high resistance of the voltage blocking layer owing to conductivity modulation [12]–[17].