Verma K C, Goyal Navdeep, Kotnala R K
Ubiquitous Analytical Techniques Division, CSIR-Central Scientific Instruments Organisation, Chandigarh 160030, India.
Department of Physics, Panjab University, Chandigarh 160014, India.
Phys Chem Chem Phys. 2019 Jun 21;21(23):12540-12554. doi: 10.1039/c9cp02285f. Epub 2019 May 31.
The induction of charge and spin in diluted magnetic semiconductor ZnO is explored for spintronic devices and its wide direct band gap (3.37 eV) and large exciton binding energy (60 meV) exhibit potential in UV photodetectors. We reported the ferromagnetic and optical properties of pure ZnO, ZnNdO and ZnSmO thin films. These thin films were synthesized by a metallo-organic decomposition method and annealed at 500 °C for 7 h. Rietveld refinement of the XRD data results in a wurtzite ZnO structure with Nd, Sm doping. The dopants and nanoparticle size are responsible for wurtzite structural deformation, inducing lattice strain effect, which may influence the band gap energy and high-T ferromagnetism of ZnO. The average size of ZnO nanoparticles with Nd, Sm doping is 10 nm, confirmed with atomic force microscopy. The Raman spectra confirm the wurtzite structure of ZnO with crystalline quality and lattice defect formation with dopant Nd, Sm ions. A near-band-edge emission due to band gap energy is evaluated with photoluminescence spectra, which also involved multiple visible emissions due to oxygen vacancies. The oxygen vacancies-mediated magnetic interactions impart room temperature ferromagnetism in pure ZnO which is enhanced with Nd, Sm doping. The electron paramagnetic resonance spectra revealed the effects of defects and unpaired electrons responsible for observed room temperature ferromagnetism. The zero field cooling and field cooling magnetic measurements include antiferromagnetic interactions without any spin-glass formation. The observed ferromagnetism also correlates with first principle calculations reported for Nd, Sm-doped ZnO and suggests long-range ferromagnetic ordering attributed to defect carriers. The Nd, Sm doping into ZnO thin films significantly enhances absorption in the UV region and suggests its usability for UV detectors. Under UV irradiation (λ = 325 nm), the value of photocurrent in Nd, Sm:ZnO thin films is highly enhanced for possible use in UV sensors.
研究了稀磁半导体ZnO中电荷和自旋的诱导，用于自旋电子器件，其宽的直接带隙（3.37 eV）和大的激子结合能（60 meV）在紫外光探测器中显示出潜力。我们报道了纯ZnO、ZnNdO和ZnSmO薄膜的铁磁和光学性质。这些薄膜通过金属有机分解法合成，并在500°C下退火7小时。对XRD数据进行Rietveld精修，得到了Nd、Sm掺杂的纤锌矿ZnO结构。掺杂剂和纳米颗粒尺寸导致纤锌矿结构变形，引发晶格应变效应，这可能会影响ZnO的带隙能量和高温铁磁性。用原子力显微镜证实，Nd、Sm掺杂的ZnO纳米颗粒的平均尺寸为10 nm。拉曼光谱证实了ZnO的纤锌矿结构以及掺杂剂Nd、Sm离子形成的晶体质量和晶格缺陷。用光致发光光谱评估了由于带隙能量引起的近带边发射，其中还涉及由于氧空位导致的多个可见发射。氧空位介导的磁相互作用赋予纯ZnO室温铁磁性，Nd、Sm掺杂增强了这种铁磁性。电子顺磁共振光谱揭示了导致观察到的室温铁磁性的缺陷和未成对电子的影响。零场冷却和场冷却磁测量包括反铁磁相互作用，没有任何自旋玻璃形成。观察到的铁磁性也与报道的Nd、Sm掺杂ZnO的第一性原理计算相关，并表明归因于缺陷载流子的长程铁磁有序。Nd、Sm掺杂到ZnO薄膜中显著增强了紫外区域的吸收，并表明其可用于紫外探测器。在紫外照射（λ = 325 nm）下，Nd、Sm:ZnO薄膜中的光电流值大幅增强，有可能用于紫外传感器。
