Effect of aluminum addition on the optical, morphology and electrical behavior of spin coated zinc oxide thin films

Abstract

Aluminum-doped ZnO thin films of high optical transmittance (∼ 84-100%) and low resistivity (∼ 2.3x10-2 Ωcm) have been prepared on glass substrate by the spin coating and subsequent annealing at 500°C for 1h in air or vacuum. Effect of aluminum doping and annealing environment on morphology, optical transmittance and electrical resistivity of ZnO thin films has been studied with possible application as a transparent electrode in photovoltaic. The changes occurring due to aluminum addition include reduction in grain size, root mean square roughness, peak-valley separation, and sheet resistance with improvement in the optical transmittance to 84-100% in the visible range. The origin of low electrical resistivity lies in increase in i) electron concentration following aluminum doping (being trivalent), formation of oxygen vacancies due to vacuum annealing, filling of cation site with additional zinc at solution stage itself and ii) carrier mobility

Effect of zinc addition and vacuum annealing time on the properties of spin-coated low-cost transparent conducting 1 at% Ga–ZnO thin films

“…The precursor sol described as (Zn–O–CH 2 –CH 2 –NH 2 ) upon casting a thin film and pre-heating at 400 °C for 10 min in air decomposes to ZnO [10]. The formation of oxide involves nucleation and growth processes.…”

“…Its optical bandgap ( E g ) and defect-induced band tailing parameter (Δ E u = {d[ln( α )]/d[ h υ ]} −1 ) have been obtained from ( α h υ ) 2 versus h υ or Tauc plot and ln( α ) versus h υ plot [10, 60], respectively (figures 4(c) and (d); table 1). While ZnO thin films after annealing for a short duration (i.e.…”

“…While ZnO thin films after annealing for a short duration (i.e. 15 min) display high optical transmittance of ∼90% due to low surface roughness [10], those subjected to prolonged treatment of 60 min exhibit poor transmittance, high surface roughness and a large Urbach width (Δ E u ) of ∼94 meV (notice increased bandgap tailing in figure 4(d)). The decrease in transmittance can be attributed to additional scattering resulting from the increased surface roughness of films.…”

“…Further, doped ZnO thin films have been realized by a number of sophisticated techniques such as atomic layer deposition, sputtering, chemical vapor deposition and pulsed laser deposition on different substrates (glass, quartz, Si-wafer and sapphire) with optical transmittance of ∼70–95% and electrical resistivity of ∼10 −1 –10 −4 Ω cm [6–9]. Sol-based spin coating has nowadays become attractive because of its simplicity, safety and low cost [10, 11]. …”

Effect of precursor solvent on the opto-electrical properties of spin coated transparent conducting ZnO: Ga thin films

“…In presence of alcoholic solvents, zinc acetate dihydrate transforms to zinc mono-acetate positively charge [CH 3 eCOeOeZn] þ species which, in turn, react with the monoethano-lamine stabilizer to produce a transparent sol having a network of ZneOeCH 2 eCH 2 eNH 2 connected by carbon [10,58]. For dissolution of an ionic precursor, the solvent owes its superiority to (i) polarity, (ii) high dielectric constant, and/or (iii) presence of eOH groups The values of dielectric constant of methanol, 4.…”