Diode Parameters and Equivalent Electrical Circuit Model of n-Type Silicon/B-Doped p-Type Ultrananocrystalline Diamond Heterojunctions Manufactured Through Coaxial Arc Plasma Deposition.

Coaxial arc plasma deposition (CAPD) was employed to manufacture n-type silicon/boron-doped p-type ultrananocrystalline diamond heterojunctions. Measurement and analysis of their dark current density-voltage curve were carried out at room temperature in order to calculate the requisite junction parameters using the Cheung and Norde approaches. For the calculation based on the Cheung approach, the series resistance (Rs), ideality factor (n) and barrier height (Φb) were 4.58 kΩ, 2.82 and 0.75 eV, respectively. The values of Rs and Φb were in agreement with those calculated using the Norde approach. Their characteristics for alternative current impedance at different frequency values were measured and analyzed as a function of the voltage (V) values ranging from 0 V to 0.5 V. Appearance of the real (Z') and imaginary (Z″) characteristics for all V values presented single semicircles. The centers of the semicircular curves were below the Z' axis and the diameter of the semicircles decreased with increments of the V value. The proper equivalent electrical circuit model for the manufactured heterojunction behavior was comprised of Rs combined with the parallel circuit of resistance and constant phase element.

Influence of an Annealing Temperature in a Vacuum Atmosphere on the Physical Properties of Indium Tin Oxide Nanorod Films.

In the present study, indium tin oxide (ITO) nanorod films were produced by usage of ion-assisted electron-beam evaporation with a glancing angle deposition technique. The as-produced ITO nanorod films were annealed in the temperature range of 100-500 °C for two hours in a vacuum atmosphere. The as-produced ITO nanorod films exhibited (222) and (611) preferred orientations from the X-ray diffraction pattern. After vacuum annealing at 500 °C, the ITO nanorod films demonstrated many preferred orientations and the improvement of film crystallinity. The sheet resistance of the as-produced ITO nanorod films was 11.92 Ω/ and was found to be 13.63 Ω/ by annealing at 500 °C. The as-produced and annealed ITO nanorod films had a rod diameter of around 80 nm and transmittance in a visible zone of around 90%. The root mean square roughness of the as-produced ITO nanorod film's surface was 5.49 nm, which increased to 13.77 nm at an annealing temperature of 500 °C. The contact angle of the as-produced ITO nanorod films was 110.9° and increased to 116.5° after annealing at 500 °C.

Wettability, Surface Morphology and Structural Properties of ß-FeSi2 Films Manufactured Through Usage of Radio-Frequency Magnetron Sputtering.

In this research, ß-FeSi2 thin films were manufactured onto Si(111) wafer substrates through the usage of radio-frequency magnetron sputtering (RFMS) method at 2.66 × 10-1 Pa of sputtering pressure. The substrate temperatures were varied at 500 °C, 560 °C, and 600 °C. The Raman lines of the ß-FeSi2 fabricated at 500 °C revealed the peaks at the positions of ~174 cm-1, ~189 cm-1, ~199 cm-1, ~243 cm-1, ~278 cm-1, and ~334 cm-1. For the higher substrate temperatures of 560 °C and 600 °C, the Raman peaks of ~189 cm-1, ~243 cm-1, and ~278 cm-1 were shifted toward higher Raman positions. The surface view of the films was observed with several grains over the ß-FeSi2 film surface at all substrate temperatures. The average grain size of the films for the samples deposited at 500 °C and 560 °C was in the range of 28 to 30 nm, where the size was enlarged to 36 nm at 600 °C of substrate temperature. The root mean square roughness were 10.19 nm, 10.84 nm, and 13.67 nm for the ß-FeSi2 film surface prepared at the substrate temperatures of 500 °C, 560 °C, and 600 °C, respectively. The contact angle (CA) values were 99.25°, 99.80°, and 102.00° for the created samples at 500 °C, 560 °C, and 600 °C, respectively. As the acquired CA values, all ß-FeSi2 samples exhibited a hydrophobic property with CA in the range of 90° to 150°. Consequently, the produced ß-FeSi2 film surface employing the RFMS method indicated a potential to be employed in a hydrophobic coating application.

Light Detection and Carrier Transportation Mechanism in p-Type Si/n-Type Nanocrystalline FeSi2 Heterojunctions Produced via Radio-Frequency Magnetron Sputtering.

In the current research, p-type Si/n-type nanocrystalline FeSi2 heterojunctions were fabricated at room temperature with an argon pressure of 2.66×10-1 Pa by means of the utilization of a radiofrequency magnetron sputtering technique. These heterojunctions were studied for the carrier transportation mechanism and near-infrared (NIR) light detection at various temperatures ranging from 300 K down to 150 K. At 300 K, the fabricated heterojunctions displayed a typical rectifying action together with substantial leakage current. At 150 K, the leakage current was clearly reduced by greater than four orders of magnitude. The value of the ideality factor (n) at 300 K was computed to be 1.87 and this was nearly constant under temperatures ranging from 300 down to 260 K. This implies that a recombination process was predominant. At temperatures lower than 250 K, the value of n was found to be more than 2. These results demonstrated that the carrier transportation mechanism was governed by a tunnelling process. A weak response for the irradiation of NIR light was observed at 300 K. At 150 K, the ratio of the photocurrent to the dark current evidently increased by more than two orders of magnitude. The detectivity at 150 K was 4.84×1010 cm Hz1/2 W-1 at zero bias voltage, which was clearly improved as compared to that at 300 K.

Temperature Dependence of Alternating Current Impedance in n-Type Si/B-Doped p-Type Ultrananocrystalline Diamond Heterojunctions Produced Through Pulsed Laser Deposition.

In the present research, heterojunctions comprised of n-type Si wafer substrates and B-doped p-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite films were produced successfully by using pulsed laser deposition. Their alternating current impedance characteristics, under various frequencies, were measured and studied as a function of temperature in the range 200 to 400 K. Both the real (Z') and imaginary (Z″) parts of the complex impedance were temperature dependent. It was apparent that the Z″-Z' curve for all temperatures exhibited single semicircles. The center of these semicircles was below the Z' axis. With temperature increment, the diameter of the semicircles decreased. The characteristics of the semicircular curve indicated that the parallel resistance (Rp) and constant phase element (CPE) in parallel combination with the series resistance (Rs) should be appropriate for the equivalent electrical circuit model for the produced heterojunctions. Through simulation, the value of Rs at 200 K was found to be 5.04×10³ Ω, and fell to 252.05 Ω at 400 K. Also, the value of Rp was 1.34×107 Ω at 200 K and decreased to 3.37×105 Ω at 400 K. Moreover, the value of CPE at 200 K was 95.91×10-12 F with a deviation from the standard (n) value of 0.90 and rose slightly to 115.60×10-12 F with an n value of 0.98 at 400 K.

Extraction of J-V, G/ω-V-f and C-V-f Characteristics for p-Type Silicon/Intrinsic Ultrananocrystalline Diamond/n-Type Nanocrystalline Iron Disilicide Heterojunction Photodiodes.

The production of p-type silicon/intrinsic ultrananocrystalline diamond/n-type nanocrystalline iron disilicide heterojunction devices was conducted via coaxial arc plasma deposition and pulsed laser deposition. The results of current density-voltage (J-V) curves justified a large leakage current along with minimal response under illumination. A recombination process controls the mechanism for carrier portage in the zone of V ≤ 0.16 V, while a space-charge-limited current process governs the carrier portage mechanism in the circumstance of V value beyond 0.16 V. Frequency (f) dependent conductance (G/ω)-V and capacitance (C)-V curves were measured to extract the series resistance (Rs) and density of the interface state (nss). On the basis of extraction in the manner of Nicollian-Brews, the value of Rs rose with f abatement. With zero bias voltage applied, the value of Rs was 189.84 Ω at 2 MHz and rose to 715.10 Ω at 20 kHz. The acquired Rs may be attributable to the occurrence of Rs in the neutral zones as well as Ohmic contact. The values for nss, which were extracted in the manner of Hill-Coleman, were 1.23×1011 eV-1 cm-2 at 2 MHz and 6.51×1012 eV-1 cm-2 at 20 kHz. This result was an indicator of the occurrence of interface states at the zone of the junction interface performing as a source of leakage current and a trap center for the carriers originated by light.

Influence of Annealing Temperature on Mechanical and Wetting Properties of ß-FeSi2 Films Built Using Facing-Targets Direct-Current Sputtering.

In this research, ß-FeSi2 films were formed on Si(111) wafer substrates via the utilization of facingtargets direct-current sputtering (FTDCS). The sputtering pressure was set at 1.33×10-1 Pa and the substrate temperature was maintained at 600 °C. After formation, the as-formed ß-FeSi2 films were transferred to the annealing system and annealed for two hours in a vacuum at 200, 400, and 600 °C. The peaks of the Raman line were located at positions of 194 and 247 cm-1, which affirmed the formation of the ß phase for the as-produced FeSi2 films. These peak positions were not changed significantly by annealing. FESEM imagery of the as-formed ß-FeSi2 films exhibits a large amount of crystallite with an average grain size of 114.11 nm, including many grain boundaries and a porous area. After annealing, the porosity of the film surface was diminished and grain size was expanded. The rms roughness of the as-formed ß-FeSi2 films was 2.02 nm, which changed slightly after annealing. The average contact angle between the water droplet and as-formed ß-FeSi2 film surface was found to be 93.25°. This result showed that the surface of the unannealed ß-FeSi2 films was hydrophobic. The average contact angle value decreased to 82.15° at an annealing temperature of 600 °C. The hardness of the ß-FeSi2 film surface was 37.55 GPa and 64.88 GPa in cases of non-annealing and annealing temperatures of 600 °C, respectively.

C-V-f, G-V-f and Z″-Z' Characteristics of n-Type Si/B-Doped p-Type Ultrananocrystalline Diamond Heterojunctions Formed via Pulsed Laser Deposition.

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.

Effect of Annealing on Surface Morphology and Wettability of NC-FeSi2 Films Produced via Facing-Target Direct-Current Sputtering.

Nanocrystalline iron disilicide (NC-FeSi2) films were created at room temperature by facing-target direct current sputtering. The NC-FeSi2 films were annealed at different temperatures of 300 °C, 600 °C, and 900 °C under high vacuum for 2 hours. XRD results of the as-created NC-FeSi2 films after annealing at 300 °C showed a broad peak at 2 ranging from 40° to 50°. NC-FeSi2 films annealed at 600 and 900 °C consisted of several preferred orientations with improved crystallinity. Peaks of Raman lines for unannealed and annealed NC-FeSi2 films were observed at approximately 176 and 232 cm-1, respectively. Based on FESEM micrographs in plane view, unannealed NC-FeSi2 films were composed of many small uniform crystallites with diameters of 5-7 nm. At an annealing temperature of 300 °C the small uniform crystallites merged and formed small nanocrystalline clusters, while at annealing temperatures higher than 300 °C they grouped together as large clusters. An AFM of unannealed NC-FeSi2 films showed a very smooth surface with a root mean square roughness of 0.81 nm which increased by annealing. Unannealed NC-FeSi2 film surface exhibited an average contact angle of 100.1°, which was hydrophobic. At an annealing temperature of 300 °C, the film surface exhibited the highest contact angle of 106.2°. Average contact angles decreased at annealing temperatures higher than 300 °C.

Study of Annealing Influence on Basic Properties of Indium Tin Oxide Nanorod Films Deposited Using Glancing Angle Ion-Assisted Electron Beam Evaporation.

Indium tin oxide (ITO) nanorod films were deposited onto glass slides and Si wafers using ionassisted electron beam evaporation with a glancing angle deposition technique. The annealing influence on the basic properties of the as-deposited ITO nanorod films was studied in the range of 100-500 °C for two hours in air. The crystallinity of the ITO nanorod films was enhanced with the increasing annealing temperature, and the average transmission of the as-deposited ITO nanorod films in the visible range was 90%. This value did not change significantly after the annealing process. The optical bandgap of the as-deposited ITO nanorod films was 3.94 eV and increased slightly after annealing. The sheet resistance of the as-deposited ITO nanorod films was 12.9 Ω/ and increased to 57.8 Ω/ at an annealing temperature of 500 °C. The as-deposited ITO nanorod films showed nanorod structures with average diameters of 79 nm, which changed slightly with the annealing temperature. The root mean square roughness of the as-deposited ITO nanorod films was 7.9 nm and changed slightly with annealing. The as-deposited ITO nanorod films had an average contact angle of 110.9°, which decreased to 64.2° at an annealing temperature of 500 °C. The experimental results showed that varying the annealing temperature influenced the structural, electrical and wettability properties of the ITO nanorod films while the optical properties and surface morphology were almost unaffected.

Photovoltaic Properties and Series Resistance of p-Type Si/Intrinsic Si/n-Type Nanocrystalline FeSi2 Heterojunctions Created by Utilizing Facing-Targets Direct-Current Sputtering.

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.

Diode Parameters of Heterojunctions Comprising p-Type Ultrananocrystalline Diamond Films and n-Type Si Substrates.

In the current research, heterojunctions comprising p-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films and n-type Si substrates were formed via pulsed laser deposition. To extract their junction parameters via thermionic emission (TE) theory and Norde model, the measurement of dark current density-voltage curves was carried out under various temperatures ranging from 300 to 60 K. Through TE theory, the ideality factor values at 300 K and 60 K were 2.70 and 8.66, respectively. This justified that a heavy recombination process occurs at the junction interface in addition to another tunneling process at 300 K. The tunneling process is predominant at low temperatures. The barrier height values were 0.78 eV and 0.18 eV at 300 K and 60 K, respectively. The values for series resistance (Rs) calculated via Norde model at 300 K and 60 K were 275.24 Ω and 78.66 kΩ, respectively. The increment of Rs at low temperatures was likely due to the decrease of carrier concentration in the B-doped UNCD/a-C:H films when temperature was decreased.