Papers by Keyword: OCVD

Abstract: The free electron lifetime is a key factor in determining the performance of a dye-sensitized solar cells (DSCs). Open-circuit voltage-decay (OCVD) suggested by Zaban is a useful technique to provide continuous reading of the electron lifetime as a function of device’s open-circuit voltage (Voc), but the data processing has never been studied in order to get high accuracy electron lifetime value from the high resolution decaying voltage data. In this manuscript, we introduce the variable rank differential smoothing (VRDS) technique in the electron lifetime data processing. We find it can lessen data loss and give highly accurate electron lifetime value in the range of Voc decaying. We also get the effective recombination order values based on the VRDS technique, which indicate different potential processes due the two different values. These results show the detail kinetics information and microscopic device physic characteristics, which are very important to understand the device working mechanism and meaningful for realizing higher performance solar cells.

Abstract: The reverse and forward currents of Al⁺ ion implanted 4H-SiC p⁺-i-n diodes have been compared for identically processed devices except for the implanted Al concentration in the emitter, 6×10¹⁹ cm^-3 against 2×10²⁰ cm^-3, and the post implantation annealing treatment, 1600°C/30 min and 1650°C/25 min against 1950°C/5min. The diodes’ ambipolar carrier lifetime, as obtained by open circuit voltage decay measurements, has been compared too. The devices with lower annealing temperature show lower leakage currents and higher ambipolar carrier lifetime; they also show lower current in ohmic conduction.

Abstract: We performed deep level transient spectroscopy (DLTS), in capacitance, constant-capacitance and current mode, on 5 MeV proton irradiated 4H-SiC p⁺-i-n diodes. The study has revealed the presence of several majority and minority traps, ranging in the 0.4-1.6 eV below the conduction band edge and in the 0.4-1.5 eV above the valence band edge. We present a comparison of the results obtained with the three modes and discuss the nature of the detected traps, in the light of previous results found in the literature. At last, the impact of the irradiation on the minority carrier lifetime is evaluated by electrical measurements.

Abstract: In this contribution, we report on the electrical characterization of point defects in 4H-SiC p⁺in diodes. Ten electrically active levels have been detected in the base region of the devices, by employing Deep Level Transient Spectroscopy (DLTS) and Minority Carrier Transient Spectroscopy (MCTS). Of these ten levels, six are majority carrier traps, in the 0.1-1.7 eV energy range below the conduction band edge, and four were minority carrier traps located in the 0.13-0.4 eV energy range above the valence band edge. We found that, during DLTS measurements, both majority and minority carrier traps can be detected and we explain this by considering the behavior of the quasi-Fermi levels. At last, we studied the impact of proton irradiation on the minority charge carrier lifetime.

Abstract: In this paper we report on the effect of temperature and injection level on the effective lifetime of non-equilibrium charge carriers in p-base of 4H-SiC PiN diodes. Studies were carried out on 1kV drift step recovery diodes (DSRDs) with p⁺-p^--n⁺. The lifetime of non-equilibrium charge carriers in 4H-SiC p⁺-p^--n⁺ structures increases by an average of 6 times from 250ns to 1.4μs with the increase of the samples temperature from 300K to 673K. However, increase of the injection level in the drift region from 2.3·10¹⁶cm^-3 to 5.9·10¹⁶cm^-3 does not affect the lifetime indicating that Shockley-Read-Hall recombination processes are dominating.

Abstract: Sharp avalanche breakdown voltages of 12.9 kV are measured on PiN rectifiers fabricated on 100 µm thick, 3 x 10¹⁴ cm-3 doped n- epilayers grown on n+ 4H-SiC substrates. This equates to a record high 129 V/µm for a > 10 kV device. Optimized epilayer, device design and processing of the SiC PiN rectifiers result in a > 60% blocking yield at 10 kV, ultra-low on-state voltage drop and differential on-resistance of 3.75 V and 3.3 mΩ-cm² at 100 A/cm² respectively. Open circuit voltage decay (OCVD) measured carrier lifetimes in the range of 2-4 µs are obtained at room temperature, which increase to a record high 14 µs at 225 °C. Excellent stability of the forward bias characteristics within 10 mV is observed for a long-term forward biasing of the PiN rectifiers at 100 A/cm2. A PiN rectifier module consisting of five parallel large area 6.4 mm x 6.4 mm 10 kV PiN rectifiers is connected as a free-wheeling diode with a Si IGBT and 1100 V/100 A switching transients are recorded. Data on the current sharing capability of the PiN rectifiers is also presented.

Abstract: This paper reports on the influence of temperature on the electrical carrier lifetime of a 3.3 kV 4H-SiC PiN diode processed with a new generation of SiC material. The Open Circuit Voltage Decay (OCVD) is used to evaluate ambipolar lifetime evolution versus temperature. The paper presents a description of the setup, electrical measurements and extraction fittings. The ambipolar lifetime is found to rise from 600 ns at 30 °C to 3.5 μs at 150 °C.

Abstract: Lifetime measurements are performed on 4H-SiC pin power diodes (6.5 kV). The lifetime values in the base range from 1.1 s to 2.1 s; these values demonstrate the high quality of the 4H-SiC epilayer and the optimized device processing. The observed lifetimes are correlated with deep defect centers detected by deep level transient spectroscopy. The role of the Z1/2-center as a lifetime killer is discussed.