新型SnO2基超宽禁带合金半导体设计、禁戒跃迁解除与日盲紫外光探测器探索

Ultra-wide band gap semiconductors become a hot issue in the semiconductor field, due to their great potential applications in deep ultraviolet photoelectric device. Typical wide band gap semiconductor SnO2 has applied widely as transparent conductive electrodes, gas sensors and so on. However, the dipole forbidden transition of SnO2 restricts it as active layer in photoelectric devices. In this proposal, we propose to induce the unfilled d shell of Zr or Hf to hybrid with the p orbital of O in SnO2 and change the symmetry of the valence band maximum to break the dipole forbidden transition. Meanwhile, it makes the band gap wider. We can achieve the ultra-wide band gap of Zr(Hf)-SnO2 semiconductor alloy with direct transition and apply them as deep ultraviolet photo detectors. In this project, we will employ the first-principles calculations with the cluster expansion method theoretically to investigate the mechanism of removing the forbidden-transition by p-d hybridization and the effect of controlling the intrinsic defect by inducing Zr or Hf. And then, we will grow the Zr(Hf)-SnO2 epitaxial films by pulsed laser deposition method and study the crystal structures, solubility limitation, optical and electrical properties, and the performances of deep UV detectors to discover the mechanism of adjusting the electronic band and removing the forbidden-transition by Zr or Hf. It will guide the band engineering of SnO2 and its application as solar blind UV detectors in theory and in technology.

超宽禁带半导体因其在深紫外光电器件等领域的广泛潜在应用而成为半导体材料领域的研究热点之一。典型宽禁带半导体SnO2基材料已广泛用于透明导电电极和气体探测等领域，但其禁戒跃迁却限制了其在光电有源器件中的应用。本项目提出通过引入Zr或Hf的未满d轨道与SnO2的O 2p轨道进行杂化，改变价带顶的对称性从而消除禁戒跃迁；同时利用Zr、Hf氧化物拓宽合金带隙，获得直接跃迁的超宽禁带Zr或Hf掺杂SnO2合金，并探讨其在深紫外光电器件上的应用。本项目将在第一性原理对p-d杂化消除禁戒跃迁机制及Zr、Hf对合金本征缺陷调控作用等理论研究基础上，采用脉冲激光沉积生长Zr(Hf)-SnO2外延薄膜，深入研究合金晶体结构、固溶度极限、能隙宽度与光电特性，以及模型光电器件特性参数等, 揭示Zr（Hf）掺杂对合金能带调控规律及禁戒跃迁解除机制，为SnO2能带工程及其在日盲紫外光探测器应用提供理论依据和技术基础。

宽禁带半导体常用于日盲紫外光探测和功率电子器件。虽然SnO2具有3.6 eV的本征带隙，但是由于其具有强烈的持续光电导效应、禁戒跃迁的限制，以及低于UVC波段的光学带隙，限制了其在日盲紫外光探测领域的应用。同时由于其p型掺杂困难且难以与金属形成肖特基结，限制了其在功率电子器件领域的应用。. 本项目通过在SnO2外延薄膜中掺杂Zr、Hf元素，成功地将合金半导体的光学带隙拓展至4.5 eV以上，部分解除了禁戒跃迁的限制，同时又极大降低了氧空位，消除了持续光电导现象，实现了高性能的日盲紫外光探测。本项目实现了高含量Zr、Hf掺杂SnO2，确定了Zr与Hf在SnO2中的固溶度。揭示出Zr、Hf掺杂对SnO2带隙的影响机制为O的2p轨道与掺杂元素的d轨道相互作用推高了导带，从而实现带隙的拓宽。阐明了Zr、Hf的d轨道与Sn的s轨道共同构成导带底从而解除禁戒跃迁的微观机制。同时发现了Zr、Hf掺杂对SnO2中氧空位的抑制机制为Zr-O（Hf-O）键强于Sn-O键，从而锚定了O原子，极大降低了O空位的浓度，从而降低了背景载流子浓度。Zr、Hf的掺入也使得O空位的缺陷能级变得更深，从而在受到光激发后也不会与导带共振，是消除持续光电导效应的微观机制。对Zr、Hf掺杂SnO2的n型与p型掺杂进行了探索研究，实现了紫外导电外延薄膜，发明了两步法实现对SnO2的p型掺杂。构造出高性能的SnO2同质pn结紫外光探测器，实现了对紫外光的自驱动探测和0.5 ms的高响应速度。研制出高耐压的SnO2二极管，实现了高达116 V的反向击穿电压。揭示出SnO2难以与金属形成肖特基结的主要原因是SnO2表面O空位形成能小于0，能自发形成O空位，从而形成高浓度的表面电荷积累层降低了势垒高度。低价元素的表面掺杂实现了SnO2肖特基结的可靠制备。. 本项目的研究成果对于深入开发SnO2光电器件具有非常重要的意义。带隙调控机制、禁戒跃迁接触机制、O空位抑制机制、p型掺杂方法等微观机制和方法对于研究其他半导体材料具有借鉴意义。有望使得SnO2在日盲紫外光探测与功率电子器件领域得到广泛应用。