Optoelectronic properties of phosphorus doped p-type ZnO films grown by dual ion beam sputtering

Abstract

We report highly conductive and stable p-type phosphorus doped ZnO (PZO) thin films fabricated by dual ion beam sputtering and subsequent thermal annealing. Hall measurements established that the annealed PZO films were p-type, which were also confirmed by typical diode-like rectifying current-voltage (I-V) characteristics of the p-PZO/n-Si heterojunction. The maximum hole concentration was evaluated to be 8.62 × 1019 cm−3 with a resistivity of 0.066 Ω cm and a mobility of 1.08 cm2/V s at room temperature. The stability of the p-type conduction was verified by Hall measurement performed again after one year of thin film fabrication resulting in a hole concentration of 3.77 × 1019 cm−3. Spectroscopic ellipsometry was employed to determine the complex dielectric function (ε=ε1+iε2) of p-type PZO films in the 1.2–6.4 eV energy range by a parameterized semiconductor oscillator model. Room temperature excitonic features were identified and the critical point energy was determined by second order derivative of imaginary part of dielectric function. The line shape analysis of ε resulted in a red shift of the energy positions of the critical point with an increase in hole concentration.