【作者】 李洋；

【导师】 叶志镇；

【作者基本信息】 浙江大学 ， 材料物理与化学， 2014， 博士

【摘要】 氧化锌(ZnO)是Ⅱ-Ⅵ族宽禁带的直接带隙化合物半导体材料,禁带宽度为3.37eV,激子束缚能60meV,是制备发光二极管和半导体激光器的一种有潜力的材料。由于ZnO通常沿着c轴方向生长,具有很强的自发极化和压电极化效应,在这个方向制备的量子阱有很强的内建电场,导致制备出的光电器件发光效率较低,发光峰红移。通过沿着垂直与c轴方向也就是非极性方向生长薄膜可以消除内建电场的影响。因此,我们开展非极性薄膜的生长、合金化和多量子阱研究,并采用IA族元素Na作为p型掺杂剂,开展了Na掺杂的非极性ZnO研究,为实现ZnO基光电器件应用探索出一条新的道路。本论文的研究工作主要包括以下内容：1.利用脉冲激光沉积技术在m面蓝宝石衬底上外延m面ZnO薄膜,系统的研究了生长温度、沉积压强对薄膜的影响。结果表明得到的ZnO薄膜都是沿着非极性m面方向生长的,不含有极性和半极性成分,在较高的温度和较低的压强下制备的薄膜晶体质量比较好。在r面蓝宝石上外延出a面ZnO薄膜,薄膜的摇摆曲线半高宽仅有0.47°,表面粗糙度1.7nm,比m面ZnO薄膜有更好的晶体质量。2.采用PLD方法在r面蓝宝石上制备了Na掺杂的非极性a面ZnO薄膜,实现了非极性a面ZnO薄膜的p型转变。研究了Na含量、生长温度和沉积压强对电学性能的影响。得到的p型薄膜最佳的电学性能为：电阻率102Ωcm,空穴迁移率1.41cm2/Ⅴ、s,载流子浓度5.19×1016cm-3。制备出a面取向的ZnO同质p-n结,I-V特性曲线有一定的整流效应,验证了薄膜的p型导电行为。3.制备出较好晶体质量的非极性ZnMgO和非极性ZnCdO薄膜,实现了非极性ZnO薄膜的带隙调节。研究了生长温度和压强对非极性ZnMgO薄膜的晶体质量和性能的影响。在550℃,1Pa下制备的非极性ZnMgO薄膜具有最好的晶体质量,摇摆曲线半高宽为0.53℃,AFM测试得到的表面粗糙度仅为1.54nm。Hall测试得到薄膜的电阻率为1.51Ωcm,载流子迁移率7.74cm2/Vs,载流子浓度1.88×1018cm-3,呈n型导电。通过改变沉积压强,我们可以引入13%的Cd而不出现分相,但此时是以极性取向占主导,可以引入7.2%的Cd而薄膜仍然保持单一的a面非极性取向,实现禁带宽度从3.30到3.01eV内变化。4.在r面蓝宝石上制备了一系列不同阱宽的10周期ZnMgO/ZnO多量子阱,阱宽从2.2到5.6nm范围内变化。XRD测试表明量子阱沿着a面(1120)方向生长,具有单一的非极性择优取向。截面TEM测试表明量子阱有很好的周期性以及陡峭的界面。观察到了不同阱宽量子阱在低温和室温下的量子限域效应。研究了量子阱中的激子局域化效应、激子束缚能和温度淬灭效应。在c面蓝宝石上我们采用相同的方法制备了一系列与a面多量子阱相同阱宽的c面多量子阱,发现在我们所设计的阱宽范围内,非极性多量子阱没有出现发光峰的红移,极性多量子阱在阱宽大于5nm后出现了明显的红移现象,也即量子限域斯塔克效应,同时非极性多量子阱比极性多量子阱有更高的电子-空穴限制效率,这对光电器件的应用有非常重要的意义。更多还原

【Abstract】 Zinc Oxide (ZnO), as a novel II-VI compound semiconductor with direct band gap of3.37eV and large excition binding energy of60meV, has been considered one of the most promising materials for short wavelength optoeletronic devices such as light-emitting diodes (LEDs) and laser diodes (LDs). However, with polar c-axis as the natural growth direction, ZnO suffers build-in electric fields along [0001] direction due to strong spontaneous and piezoelectric polarization, which will cause a decrease in the internal quantum efficiency of LEDs. The way to remove the build-in electric fields is to grow ZnO film along the direction perpendicular to the c-axis, called "non-polar" ZnO film. In this work, we performed systematic study of growth and properties of non-poplar ZnO films, alloys and multiple quantum wells (MQWs). We investigate the growth and characterization of Na-doped non-poplar ZnO films in attempt to obtain p-type non-poplar ZnO films. The main work included:1. Non-polar m-plane ZnO films were deposited on m-plane sapphire substrates by pulsed laser deposition. The effects of growth temperature and oxygen pressure on the structural, electrical and optical properties were systematic studied. All films we prepared were grown along m-plane direction without any polar and semipolar components. We also prepared a-plane ZnO films on r-plane sapphire substrates. The full width at half maximum (FWHM) and surface roughness results were0.47℃and1.7mm respectively, indicating better crysatal quality than the m-plane ZnO film grown on m-plane sapphire substrate.2. Non-polar Na-doped ZnO films were deposited on r-plane sapphire substrates by pulsed laser deposition, and the p-type conduction non-polar ZnO films were obtained. The effects of growth temperature and oxygen pressure and Na doping concentration on the electrical properties of the films were systematic investigated. The minimum resistivity was102Ωcm, with hole mobililty of1.41cm2/Vs and hole concentration of5.19x1016cm-3, We prepared ZnO-based p-n homojunction grown along a-plane direction. The obvious rectify effect of the p-n homojunction detected by I-V curve confirms the p-type conductivity of the Na-doped non-polar a-plane ZnO film.3. The band gap modulation of non-polar ZnO film was achieved by preparing high quality non-polar ZnMgO and ZnCdO films. The effects of growth temperature and oxygen pressure on the structural and properties of the non-polar ZnMgO films were investigated. The minimum FWHM of0.53°and surface roughness of1.54nm for the non-polar ZnMgO films was obtained at550℃and1Pa, corresponding to the resistivity was1.51Ωcm, with electron mobililty of7.74cm2/Vs and carrier concentration of1.88x1018cm-3. By changing the oxygen pressure, the maximum Cd content of13%in the non-polar ZnCdO film can be achieved without any second phases and the band gap can be modulated from3.01to3.30eV. The film absorbed13%Cd will mainly grow along [0001] direction. By introducing7.2%Cd, the film was unique non-polar a-plane direction.4. A series of10-period ZnO/ZnMgO multiple quantum wells (MQWs) with well widths varying from2.2to5.6nm have been grown on r-plane sapphire substrates by pulsed laser deposition. XRD reveal the MQWs grow along a-plane (1120) direction. A good periodic structure with clear interfaces was observed by transmission electron microscopy (TEM). The systematic blueshift for the emission energy in the MQWs behavior was observed at room and low temperature. The polar ZnO/ZnMgO MQWs fabricated on c-plane sapphire substrates with the same well width were also discussed. Low temperature photoluminescence (PL) is investigated to reveal that the non-polar MQWs exhibit confinement but no indication of quantum confined Stark (QCS) effect when well width is larger than5nm, contrary to what is observed in polar MQWs, and the non-polar MQWs have higher injection effect.更多还原