Role of Ga-substitution in ZnO on defect states, carrier density, mobility and UV sensing

Gallium (Ga³⁺) doped ZnO with compositions Zn_1−xGa_xO (0 ≤ x ≤ 0.0468) is prepared using the sol–gel method. ZnO Wurtzite structure having space group P6₃mc is confirmed by using X-ray diffraction (XRD) measurement. The lesser ionic radii (0.62 Å) and higher charge (3+) of Gallium attracts more oxygen into the lattice and therefore a reduction in oxygen vacancies (V_O) is observed. Photoluminescence (PL) study reveals that defects present in ZnO lattice decreases with Ga substitution. This is also reflected in Urbach energy study. Enhancement in yellow emission in higher doped sample indicates the increases in oxygen interstitials (O_i). Conductivity increases due to rise of carrier concentration and mobility of the charge carriers. Interestingly p-type conduction is obtained in Ga-substituted ZnO samples. UV-sensing enhances with substitution too, i.e. photocurrent increases. However, the dark current plays crucial role in sensitivity. Reduction in oxygen vacancy, increase in oxygen interstitials and carrier recombination controls the recovery and response time.