Preparation of p-/n- type ZnO:Al thin films by RF diode sputtering for solar and optoelectronic applications

Aluminum - doped ZnO thin films (ZnO:Al) and Al - N co-doped (ZnOALN) thin films were prepared by RF diode sputtering from a ceramic target (ZnO+2 wt. % AI
₂
O
₃
) in Ar and Ar/25divide75 %N
₂
atmosphere. The ZnOAl films exhibited n-type conduction with a minimum resistivity (2times10
^-3
Omegacm), a high visible transmittance (> 82 %, including Corning glass substrate) and an optical band gap E
_g
~ 3.3 eV. The p-type doping efficiency of the nitrogen was investigated as a function of the nitrogen content in the sputtering gas. The ZnO:Al:N thin films with p-type conduction were obtained for 75 % N
₂
in the Ar/N
₂
gas. Their resistivity and the hole concentration were 21 Omegacm and 7.8times10
¹⁷
cm
^-3
respectively. The micro-Raman scattering measurements revealed N - related local vibrational modes (LVMs) at 276.44 cm
^-1
and 518.47 cm
^-1
in the spectra of the films grown with nitrogen and proved that the p-type conduction was a result of the nitrogen incorporation and formation of N
_O
acceptors. The average transmittance (74divide86%, including Corning glass substrate) and E
_g
(3.22 - 3.10 eV) depended on the N
₂
content in the sputtering gas. The p-/n-type ZnO thin films were utilized for preparing p-n heterojunction structures on (100) n-type and (111) p-type silicon substrates. Rectification was clearly observed for both structures.