Divya Somvanshi

Sol-Gel-Based Highly Sensitive Pd/n-ZnO Thin Film/n-Si Schottky Ultraviolet Photodiodes

High-performance ultraviolet (UV) Schottky photodiodes obtained by growing Pd Schottky contacts on the sol-gel-derived n-ZnO thin films deposited on n-Si substrates have been reported in this paper. The current-voltage (I-V) measurements of the as-fabricated Schottky photodiodes show an excellent room temperature contrast ratio (i.e., the ratio of the current under UV illumination to the dark current) of ~5.332 × 103 and responsivity (i.e., the parameter characterizing the sensitivity of the device to the UV light) of ~8.39 A/W at -5 V reverse bias voltage, respectively; when the device is illuminated by an UV source of ~650 μW output power at ~ 365 nm. The measured room temperature contrast ratio and responsivity are believed to be the highest among the reported values in the literature for ZnO thin film-based Schottky photodiodes using sol-gel method.

Mean Barrier Height and Richardson Constant for Pd/ZnO Thin Film-Based Schottky Diodes Grown on n-Si Substrates by Thermal Evaporation Method

This letter reports the temperature-dependent electrical parameters of Pd/n-ZnO thin film-based Schottky diodes grown on n-Si substrates by thermal evaporation method. The parameters have been investigated by considering a Gaussian distributed barrier height across the Pd/n-ZnO interface with a standard deviation σ₀ around a mean barrier height qφB,m. As compared with the reported results, the estimated values of the Richardson constant (~19.54Acm^-2K^-2) and mean barrier height (~1.41 eV) are much closer to their theoretically predicted values of 32Acm^-2K^-2 (for m_e*=0.27 m0) and 1.42 eV (for work function of Pd = 5.12 eV and electron affinity of ZnO = 3.7 eV), respectively.

Analysis of Temperature-Dependent Electrical Characteristics of n-ZnO Nanowires (NWs)/p-Si Heterojunction Diodes

This paper presents the electrical characteristics of n-zinc oxide (ZnO) nanowires (NWs)/p-Si (100) heterojunction diodes fabricated by the oxidation of thermally deposited metallic Zn on Al:ZnO-coated p-Si 〈1 0 0〉 substrates. The electrical parameters of the n-ZnO NWs/p-Si diodes have been estimated by using the room temperature capacitance-voltage (C-V) and temperature-dependent current-voltage (I-V) characteristics of the heterojunction. The carrier concentration of the ZnO NW film and the barrier height of the diode estimated from the C-V characteristics at room temperature are 1.54 × 10 15 cm -3 and 0.75 eV, respectively. The thermionic emission model was used to analyze the temperature-dependent measured I-V characteristics to estimate the parameters of the diode. The estimated values of the barrier height and ideality factor at room temperature were 0.715 eV and 2.13, respectively. The spatial barrier inhomogeneity was included in the aforementioned analysis by assuming a Gaussian distribution for the barrier height at the n-ZnO NWs/p-Si heterojunction. The Richardson constant A* of ZnO was found to be increased from a relatively low value of 9.75 ×10 - 8 A ·cm - 2 ·K - 2 to a more realistic value of 49A ·cm - 2 ·K - 2 after incorporating the barrier inhomogeneity phenomenon in the aforementioned analysis.

Ultraviolet Detection Properties of p-Si/n-TiO 2 Heterojunction Photodiodes Grown by Electron-Beam Evaporation and Sol–Gel Methods: A Comparative Study

This paper reports a comparative study of the ultraviolet (UV) detection properties of n-TiO2/p-Si heterojunction devices fabricated using two different deposition techniques namely the electron-beam evaporation (EBE) and sol-gel (SG) methods. A systematic study has also been carried out to investigate the structural, electrical, and optical properties of the as deposited TiO2 thin films on p-Si substrates by the EBE and SG methods. The electrical parameters of both the n-TiO2/p-Si heterojunction photodiodes have been measured and compared under dark and UV illumination conditions. The SG based n-TiO2/p-Si heterojunction photodiodes are observed with an excellent contrast ratio of ~83911 at -5.2 V bias voltage, which is ~6445 times higher than the EBE-based device. The measured responsivities of the EBE and SG based devices are ~0.69 and ~1.25 A/W at a bias voltage of -10 V (Popt = 650 μW and λ = 365 nm), respectively. Thus, the n-TiO2/p-Si heterojunction diodes with SG derived TiO2 films are considered to be a better choice over the EBE-based n-TiO2/p-Si diodes for UV detection applications.

Pd/ZnO Nanoparticles Based Schottky Ultraviolet Photodiodes Grown on Sn-Coated n-Si Substrates by Thermal Evaporation Method

This paper reports the ultraviolet (UV) detection characteristics of Pd/ZnO nanoparticles (NPs) based Schottky diodes grown on Sn coated n-Si substrates by thermal evaporation method. The measured current-voltage characteristics of the Pd/ZnO NPs/Sn/n-Si diodes under both the dark and UV illumination at wavelength of 365 nm have been presented for the applied bias voltage varying from -3 to 3 V. The as-fabricated photodiodes show a high-contrast ratio (i.e., the photocurrent to dark current ratio) of ~541.34, an excellent quantum efficiency of ~68%, a reasonably good responsivity of ~0.20 A/W at 365 nm, and -3 V reverse bias voltage at room temperature.

Effect of ZnO Seed Layer on the Electrical Characteristics of Pd/ZnO Thin-Film-Based Schottky Contacts Grown on n-Si Substrates

The electrical characteristics of Pd/ZnO thin-film Schottky contacts grown on n-Si substrates with and without using a ZnO seed layer by simple thermal evaporation method have been investigated. The structural, morphological, and optical properties of the ZnO thin films were investigated using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and photoluminescence (PL) measurements. The Schottky devices with ZnO seed layer exhibits superior diode characteristics (with excellent rectification ratio of ~2.5 × 103, barrier height = 0.81 eV, and ideality factor = 1.46 at room temperature to those without using ZnO seed layer. This is attributed to the reduction of native defects states from the ZnO thin film surface caused by ZnO seed layer as evidenced by the room-temperature PL measurement. Thus, the use of ZnO seed layer on the n-Si substrates maybe treated as an effective approach for fabricating Pd/ZnO thin-film-based Schottky diodes on n-Si substrates for electronic and optoelectronic applications.

Effects of Sn and Zn Seed Layers on the Electrical Characteristics of Pd/ZnO Thin-Film Schottky Diodes Grown on n-Si Substrates

The effects of Sn and Zn seed layers on the rectifying characteristics of Pd/ZnO thin-film Schottky diodes fabricated on n-Si substrates by the thermal evaporation method have been investigated in this letter. The field emission scanning electron microscopy images show the changes in the surface morphology of the ZnO thin film from nanocrystalline to nanoparticle, and nanocrystalline to nanowires structures when the substrates for film deposition are changed from the bare n-Si to Sn seed layer-coated n-Si and from bare n-Si to Zn seed layer-coated n-Si substrates, respectively. Furthermore, a dramatic enhancement in the rectification ratio of Pd/ZnO Schottky diodes is observed from a nominal value of 1.13 × 102 at ±2 V (for the device grown on the bare n-Si substrates) to a large value of 8.85 × 102 for the device grown on Sn seed layer coated n-Si substrates and to a value of 7.564 × 103 for the Zn seed layer coated device. The effects of the seed layers on the series resistance, ideality factor, and barrier height of the Pd/ZnO thin-film Schottky devices are also investigated for the first time in this letter.

Electrical Characterization of n-ZnO Nanowires/p-Si based Heterojunction Diodes

We report electrical characteristics of n-ZnO NWs/p-Si based heterojunctions diode fabricated by oxidation of thermally deposited metallic Zn on Al:ZnO coated p-Si substrates. The surface morphology of ZnO NWs has been investigated by atomic force microscopy (AFM). The carrier donor concentration of the ZnO NW films and barrier height of the heterojunction diode estimated from the C–V characteristics are 1.54 × 1015 cm−3 and 0.75 eV respectively. The estimated values of the barrier height and ideality factor from room temperature I–V characteristic are 0.73 eV and 2.13 respectively. As obtained value of barrier height from C–V characteristic is a bit higher then I–V characteristic, indicates presence of barrier inhomogeneity at the n-ZnONWs/p-Si interfaces. Furthermore, the value of series resistance \( \left( {{\text{R}}_{\text{s}} } \right) \) has also been determined from forward bias I–V characteristics using Chueng’s function

Catalyst free growth of ZnO nanorods by thermal evaporation method

In this work, we report catalyst free growth of ZnO nanorods on n-Si substrate by a low cost thermal evaporation method. The surface morphology, chemical composition and crystalline structure of ZnO nanorods have been determined by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) spectroscopy respectively. It is found that, the as –deposited ZnO seed layer reduces lattice mismatching between ZnO and Si from 40.3 to 0.28%, therefore enhances the subsequent growth and crystalline quality of ZnO nanorods on Si substrate. The present methodology is simple, cost effective and highly applicable for synthesis of ZnO nanorods for optoelectronics applications.

Fabrication and Characterization of ZnO Nanowires by Thermal Oxidation Method

Fabrication of ZnO nanowires (NWs) by thermal oxidation method has been studied in this work. The ZnO NWs have been grown by oxidation of Zn metal foil under oxygen environment for two typical oxidation durations. We have investigated the behavior of the as-grown ZnO NWs with the change in oxidation duration at particular temperature. The changes in surface morphology and chemical composition with the variation of oxidation duration have been analyzed by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) respectively. From EDS spectra, it is confirmed that Zn metal has completely oxidized into ZnO for higher oxidation duration. In this work, the optimized duration of oxidation for growth of ZnO NWs is found to be ~60 minutes at particular temperature of 600oC. The present method provides a possible mechanism for the growth of ZnO NWs on the p-Si substrates.