Understanding and tuning of metal-insulator transition (MIT) in oxide systems is one of the interesting and active research topics of condensed matter physics. We report thickness dependent MIT in Ga-doped ZnO (Ga:ZnO) thin films grown by pulsed laser deposition technique. From the electrical transport measurements, we find that while the thinnest film (6 nm) exhibits a resistivity of 0.05 Ω-cm, lying in the insulating regime, the thickest (51 nm) has resistivity of 6.6×10-4Ω-cm which shows metallic type of conduction. Our analysis reveals that the Mott's variable range hopping (VRH) model governs the insulating behavior in the 6 nm film whereas the 2D weak localization phenomena is appropriate to explain the electron transport in the thicker Ga:ZnO films. Magnetoresistance study further confirms the presence of strong localization in 6 nm film while weak localization is observed in 20 nm and above thicker films. From the density functional calculations, it is found that due to surface reconstruction and Ga doping, strong crystalline disorder sets in very thin films to introduce localized states and thereby, restricts the donor electron mobility.

中文翻译：

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通过控制厚度实现外延 Ga 掺杂 ZnO 薄膜中的金属-绝缘体转变

理解和调整氧化物系统中的金属-绝缘体转变 (MIT) 是凝聚态物理中有趣且活跃的研究课题之一。我们报告了通过脉冲激光沉积技术生长的 Ga 掺杂 ZnO (Ga:ZnO) 薄膜中的厚度依赖性 MIT。从电传输测量中，我们发现虽然最薄的薄膜（6 nm）的电阻率为 0.05 Ω-cm，处于绝缘状态，但最厚的薄膜（51 nm）的电阻率为 6.6×10-4Ω-cm，这表明金属类型的传导。我们的分析表明，Mott 的可变范围跳跃 (VRH) 模型控制 6 nm 薄膜中的绝缘行为，而 2D 弱局部化现象适用于解释较厚 Ga:ZnO 薄膜中的电子传输。磁阻研究进一步证实了在 6 nm 薄膜中存在强局域化，而在 20 nm 及以上更厚的薄膜中观察到弱局域化。从密度泛函计算中发现，由于表面重构和 Ga 掺杂，在非常薄的薄膜中设置了强晶体无序以引入局域态，从而限制了供体电子迁移率。