RESUMO
n-Type Si/p-type B-doped ultrananocrystalline diamond heterojunction photodiodes were built using pulsed laser deposition at a heated substrate temperature of 550 °C. Following the capacitance-voltage-frequency (C-V -f) and conductance-voltage-frequency (G-V -f) plots, the series resistance (Rs) values at zero bias voltage were 154.41 Ω at 2 MHz and 1.72 kΩ at 40 kHz. Rs should be ascribed to Rs occurring in the metallic contact and the bulk resistance in the active layer. At 40 kHz, the interface state density (nss) was 1.78 x 1013 eV-1 cm-2 and dropped exponentially to 1.39 x 1012 eV-1 cm-2 at 2 MHz. An assessed nss occurring at the heterojunction interface was the cause of deterioration in the photo-detection properties. At different V values, the appearance of the real (Z') and imaginary (Z'') characteristic curves revealed single semicircles whose centers lay below the Z' axis. The magnitude of the curve was diminished with the increment of V. The particularities of Z''-Z' plots can be identified as an equivalent circuit model. The appropriate model included Rs, which was combined with the parallel circuit of resistance and constant phase element.
RESUMO
p-Type Si/intrinsic Si/n-type nanocrystalline iron disilicide heterojunctions were created by utilizing facing targets direct-current sputtering at the pressure of 1.33×10-1 Pa that investigated the photovoltaic properties. They exhibited a large leakage current and a small energy conversion efficiency of 0.62%. From using the method of Nicollian and Brews, the series resistance (Rs) values at zero bias voltage were 7.40 Ω at 2 MHz and 7.57 Ω at 50 kHz, respectively, which were in agreement with that estimated by the means of Norde. From applying the method of Hill-Coleman, the interface state density (nss) values were 3.15×1015 cm-2 eV-1 at 50 kHz and 8.93×1013 cm-2 eV-1 at 2 MHz. The obtained results revealed the presence of Rs and nss at the junction interface, which should be the potential cause of spoiled photovoltaic performance in the heterojunctions.
RESUMO
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.
