Modification of the junction parameters via Al doping in Ag/CdS:Al thin-film Schottky diodes for microwave sensors

Abstract

In this article, it is investigated the effect of Al doping in the junction parameters of Ag/CdS:Al thin-film Schottky diodes and their electrical response to microwave irradiation. Nanocrystalline CdS:Al thin-films with thicknesses between 109 and 173 nm were prepared by chemical bath deposition and, subsequently, Ag thin-films with an average thickness of 102 nm were grown on the CdS:Al using dc sputtering. The structural, chemical, morphological and optical properties of CdS:Al and Ag films were characterized by x-ray diffraction (XRD), scanning electron microscope, atomic force microscope, energy-dispersive x-ray spectroscopy and UV-Vis spectrophotometer, respectively. Current-voltage (I − V) characteristics of Ag/CdS:Al diodes, with different Al content, were obtained at room temperature in dark conditions. XRD studies shows that CdS:Al and Ag thin-films have an hexagonal and cubic structure, respectively. Crystallite sizes decreases with Al content for CdS:Al films and were found to be in the 15–40 nm range. A decrease in the intensity of the XRD main peak of CdS:Al films is observed, caused by the inclusion of amorphous Al2O3 on the CdS film. It was found that band gap of CdS:Al films increases with increasing Al content, from 2.28 eV to 2.40 eV. Based on the I − V characteristics of the diodes, their barrier height ϕ 0, ideality factor n, and series resistance R s were calculated, and it was found that these values are modified by increasing Al content in CdS films, in the ranges: ϕ 0: 0.7037–0.8426 eV; n: 3.485–4.213; R s : 0.54–9.86 MΩ. Besides, it was stated that Al doping changes the average surface roughness and the energies of the charge neutrality levels of CdS:Al films. The effects of physical properties of the films on the junction parameters of the diodes were also discussed. Finally, I − V characteristics of the Ag/CdS:Al diodes were studied under X-band microwave irradiation at room temperature in dark conditions. For a specific Al doping value, the current density across the diode during irradiation was found to be lower (0.87–11.6 mA cm−2) than unirradiated diode (1.14–15.6 mA cm−2), when the bias voltage was higher than certain value (3 V), due to an increasing temperature of the diode and the presence of Al2O3 on the CdS:Al film. This last result could be useful in a potential X-band thin-film microwave sensor.

Aluminum-doped cadmium sulfide homojunction photoelectrode with optimal film quality and water-splitting performance

“…34,35 Furthermore, due to aluminum having a smaller ionic radius than cadmium, the doping of Al 3+ in the CdS crystal lattice was expected to exhibit a diffraction pattern shift towards a greater angle. 33,36 Elemental doping commonly leads to a diffraction intensity decrease due to the decay in crystal quality, especially when there are large radius differences between the dopant and intrinsic ions. [37][38][39] Thus, to confirm the consequences of aluminum doping, characteristic XRD peaks of CdS with and without Al doping (Fig.…”

“…Among various dopants, Al is an attractive candidate due to its low synthesis cost while preserving the original lattice structure after doping. 22,33 Hence, the modification of the original CdS by constructing a homojunction with Al-doped CdS demonstrates higher suitability and feasibility.…”

Comparison of electrical characteristics of Schottky junctions based on CdS nanowires and thin film

“…CdS can be natively n-doped and the carrier density even reaches 1.6×10 18 cm −3 [4]. CdS has been widely used in sensors [5,6], photodetectors [7], light emitting diodes [8], logic circuits [9], photocatalyst for water splitting [1] as fuel cells which are applied for electrical vehicles. In addition, CdS was recognized to be the most effective heterojunction partner of II-VI solar cells and has been widely applied into these II-VI solar cells such as CdTe [10,11], CZTS [12] and Sb 2 Se 3 solar cells [13].…”

Bias voltage effect on impedance, modulus and dielectric spectroscopies of HfO2-interlayered Si-based Schottky diodes at room temperature

“…Investigating electronic infrastructures including but not limited to structural, mechanical, thermal, optical, electrical and dielectric characteristics of semiconductor-based electronic and optoelectronic devices can help improve their performance. By virtue of their ability to conduct current in one direction but not another, Schottky diodes are the basis of most semiconductor-based devices and so they were extensively researched [1][2][3][4][5][6][7][8][9][10].…”