Impurity Compensation Effect Induced by Tin Valence Change in α-Ga_1.4Sn_0.6O₃ Thin Films

Corundum-structured α-phase Ga_1.4Sn_0.6O₃ thin films have been deposited on m-plane Al₂O₃(300) substrates using laser molecular beam epitaxy technology. With increasing of the oxygen partial pressure, the crystal lattice of Ga_1.4Sn_0.6O₃ films expands due to tin ions valence changes from Sn⁴⁺ to Sn²⁺. The resistivity of the film deposited under 3 × 10^-5 Pa is 3.54 × 10⁴ Ω·cm, which decreases by about 2 orders of magnitude than that fabricated under 3 × 10^-1 Pa. The mixture valence of Sn²⁺ and Sn⁴⁺ ions leads to the impurity altitude compensation effect. The deep ultraviolet photodetector based on α-phase Ga_1.4Sn_0.6O₃ thin films was fabricated. With the oxygen partial pressure reducing gradually, the dark current and the photocurrent increase, and the relaxation time constants diminish, respectively.