The effect of Al dopant concentration on ZnO surface roughness and optical properties

Abstract : In this report we investigated the roughness, absorbance and band gap variation of ZnO in different at% Al concentrations. The ZnO semiconductors containing different Al dopant concentrations are prepared by sol-gel spin coting method on glass substrates. To define absorbance peak and also band gap width, UV-Visible spectrometry is used. Forasmuch as roughness is an important factor in optoelectronic devices, atomic force microscopy (AFM) images are taken. Although the surface is gotten smoother in low doping, the roughness is increased by adding more dopant. The band gap is also decreased by adding dopant and absorbance peak shifts in higher wavelength. Keywords: ZnO; roughness; Aluminium doping; band gap; sol-gel Introduction Recently most researches in material sciences have been concentrating on semiconductor materials with wide band gap [1]. Novel properties of ZnO such as direct band-gap of 3.37 eV, large binding energy of 60 meV at room temperature, radiation hardness, easy nanostructure fabrication, etching ability with wet chemicals and biocompatibility, make it a good choice for optoelectronic devices such as low threshold blue/UV lasers, solar cells, LEDs, sensors, display devices and photo-detectors [2-4]. Doping is a useful way for changing properties of ZnO. Various dopants such as In, Ga and Al have been used. Among those materials, doping with Al as a substitutional element can result in interesting structural, optical and electrical properties [5]. Different methods have used for preparation of ZnO and ZnO:Al thin films such as Chemical Vapor Deposition (CVD) [6], Pulsed Laser Deposition (PLD) [7], RF magnetron sputtering [8], spray pyrolysis [9-10], Physical Vapor Deposition [11] and sol-gel [12-13]. Among them sol-gel method is particularly provided ZnO colloids and films in a simple, low-cost and highly controlled way [14]. Sol–gel hydrothermal, dip coating and spin coating techniques have been utilized in the fabrication of ZnO. The properties of the ZnO films correlate with the preparation conditions and parameters [1]. Since roughness is an important parameter that influences on efficiency and contact resistance, it modifies the performance of optoelectronic devices [15-16]. In this research, it investigated the effect of ZnO doping concentration with Al dopant on the surface roughness. UV region for any sols