n-Type nanocrystalline FeSi2/p-type Si heterojunctions were formed by using facing-target direct- current sputtering at room temperature. The J-V characteristic results revealed that the reverse leakage current is large and the response under illumination of near-infrared light is very weak. The capacitance-voltage-frequency (C-V-f) and conductance-voltage-frequency (G-V-f) measurements were carried out at room temperature in order to estimate the series resistance (Rs) by using the Nicollian-Brews method and the density of interface state (Nss) by using the Hill-Coleman method. By estimation according to the Nicollian-Brews method, the Rs value increases with decreasing f value. The Rs values at zero bias voltage were 2.07 Ω at 60 kHz and 1.54 Ω at 2 MHz, which are consistent with those calculated by using the Cheung's and Norde's methods. The obtained Rs should be attributable to the Rs existing in the ohmic contact and neutral regions, which is the current-limiting factor for junctions. The nss values calculated by using the Hill-Coleman method were 2.70 × 1014 eV-1cm-2 at 60 kHz and 1.43 × 1013 eV-1cm-2 at 2 MHz. This result revealed the presence of interface states at the hetero-interface behaving as a leakage current center and a trap center of the photo-generated carrier, which degraded the junction properties at room temperature.
Heterojunctions composed of n-type β-FeSi 2 thin films and p-type Si(111) substrates were formed by radio frequency magnetron sputtering at an Ar pressure of 2.66 ' 10 %1 Pa at a substrate temperature of 560 °C. The current density-voltage (J-V ) curves of the heterojunctions measured in the dark and under illumination at room temperature showed a large leakage current under reverse bias conditions and a weak response to nearinfrared (NIR) light irradiation. From the results of the analysis of dark forward J-V curves, the dominant carrier transport mechanisms at V : 0.15 V and V > 0.15 V were considered a recombination process and a space-charge-limited current process, respectively. Both capacitance-voltage and conductance-voltage characteristics at room temperature were measured and analyzed as a function of applied frequency ( f ) ranging from 20 kHz to 2 MHz in order to estimate the series resistance (R s ) by the Nicollian-Brews method. R s was estimated as 77.79 Ω at 20 kHz. It decreased to 14.16 Ω at 2 MHz, which is expected because the charges at the interface states cannot follow the AC signal at high f values.
Without a post-annealing procedure, the β-FeSi 2 thin films are epitaxially grown on Si(111) wafer substrates via facing-targets direct-current sputtering. During epitaxial growth, the temperature for heating of substrates is maintained at 600 C. The resultant p-type Si/n-type β-FeSi 2 heterojunctions are produced. At room temperature, a large leakage current under an applied reverse bias voltage together with a small photo-detective performance is observed from the measured dark and irradiated current density-voltage curves of the created heterojunctions. Both of the conductance-voltage (G/ ω-V) and capacitance-voltage (C-V) measurements at different frequencies (f ) in the range of 5 kHz-1 MHz are performed in the dark at room temperature. The interface state density (N ss ) and series resistance (R s ) in the created p-type Si/n-type β-FeSi 2 heterojunctions are computed and analyzed from the measured C-V-f and G/ω-V-f curves. N ss is found to be 3.48 Â 10 12 eV À1 cm À2 at 5 kHz and decreased to 4.68 Â 10 11 eV À1 cm À2 at 1 MHz. Moreover, the values of R s at zero bias are 2.21 kΩ at 5 kHz and 13.66 Ω at 1 MHz. These results review the presence of N ss and R s in the created heterojunctions, and they can be the cause to degrade the heterojunction performance.
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