摘要
摘要
Ga2O3是一种很重要的宽禁带半导体材料，它有很好的热稳定性，且击穿电压高，电子漂移速度大。因此，Ga2O3成功地被应用于MESFET，MOSFET，SBD等功率器件中。另外，在紫外光电器件，半导体激光器和太阳能电池等方面，Ga2O3也是一种很有应用前景的材料。为了实现高灵敏度且波长可调的光电探测器，且发挥Ga2O3的宽禁带特性，研究者们通过掺铝成功提高了Ga2O3薄膜的禁带宽度。本征缺陷在材料的特性上起了重要作用，然而并未有人结合本征缺陷系统地从理论上研究过Al掺杂Ga2O3。另外，由于Ga2O3中本征缺陷特别是氧空位的存在，本征Ga2O3通常呈现n型，而高载流子浓度的高质量的p型Ga2O3的发展十分困难。基于以上两个方面，本文对于铝掺杂Ga2O3缺陷复合体系进行了理论研究，对于镁与氮p型掺杂氧化镓进行了理论及实验研究。主要工作及结论如下：
1.在铝掺杂氧化镓方面，本文基于密度泛函理论研究了在铝掺杂Ga2O3体系中，本征缺陷对于其电学及光学特性的影响。考虑了四种缺陷复合体系：Al Ga2O3V O(Al 掺杂Ga2O3结合氧空位缺陷), Al Ga2O3V Ga(Al掺杂Ga2O3结合镓空位缺陷), Al Ga2O3Ga i (Al掺杂Ga2O3结合镓间隙缺陷)以及Al Ga2O3O i (Al掺杂Ga2O3结合氧间隙缺陷)。计算结果表明Al掺杂本征Ga2O3会导致氧间隙缺陷的形成。并且，Al掺杂体系Al Ga2O3禁带宽度为4.975eV，略大于本征氧化镓。当氧空位存在时，禁带中出现了深施主能级，而氧
间隙并未能引起缺陷能级的存在。铝掺杂后，本征吸收带边发生轻微蓝移，当氧空位缺陷引入后，在3.69eV处出现了新的吸收峰。
2.对于Mg掺杂氧化镓进行仿真，发现引入Mg后，Ga2O3禁带中距价带顶2.13eV 处出现能级，我们预测这是Mg对于Ga2O3引入的受主能级。为了从实际上进一步探索，我们进行了相应Mg离子注入实验，探索了Mg注入Ga2O3后，薄膜的结构特性，表面形貌，电学和光学特性。离子注入后，薄膜晶粒尺寸变小，拉曼峰的变化主要发生在高频区域，可能因为Mg离子注入主要影响GaO4四面体。随着Mg注入剂量的增大，(-402)面的XRD衍射峰位左移。当注入剂量最大的时候，2θ位于45.8°处出现了MgO2的衍射峰。Ga2O3结构多晶化，结晶质量下降。退火后，各样片薄膜晶粒尺寸变大，拉曼谱趋于与原片一致，Mg1Ga2O3和Mg3Ga2O3样片(-402)面对应的XRD衍射峰增强。说明经过高温退火处理，原子获得能量迁移到正常格点位置，薄膜晶体结晶质量提高。通过对样片的I-V，C-V测试，提取出各样片的载流子浓度，发现随着Mg注入剂量增大，Ga2O3中载流子浓度逐渐降低，证明Mg注入具有补偿效应，样片倾向于半绝缘，并未能形成p型Ga2O3薄膜。而退火之后对应的样片载流子浓度降低，可能是高温退火激发了注入的Mg离子，使得补偿效应增强所致。Mg离子注入
I
西安电子科技大学硕士学位论文
实验虽然并未能得到p型的Ga2O3，但本文对于其掺杂后薄膜特性的探索有利于今后Mg掺杂Ga2O3绝缘薄膜的应用。
3.结合N掺杂氧化镓的仿真结果（N掺杂Ga2O3在距价带顶1.33eV的禁带中引入了受主能级，可以预测N是受主杂质），进一步进行相应N离子注入实验，探索N 注入Ga2O3后，薄膜的结构特性，表面形貌，电学和光学特性。离子注入后，631.9cm-1处拉曼峰下降，658.9cm-1附近拉曼峰增强，并且产生767cm-1的拉曼峰。随着注入剂量的增加，O1s，Ga3d，Ga2p处的XPS信号峰向高结合能侧移动，这可能因为形成GaN的缘故。注入剂量最大时，2θ位于35.2°和45.86°处出现了新的XRD衍射峰，其中35.2°处峰对应GaN的(101)面，45.86°处新的衍射峰对应Ga2O3(600)面，说明离子注入使得表面损伤，结构出现多晶，结晶质量下降。退火后，631.9°附近拉曼峰有恢复的趋势，然而没有形成与原片类似的拉曼谱；样片的均方根粗糙度降低，薄膜晶粒尺寸变大；两处新的XRD衍射峰消失。这说明经过高温退火处理，薄膜结晶质量提高。通过对样片的I-V，C-V测试，提取出各样片的载流子浓度，发现随着N注入剂量增大，其载流子浓度逐渐降低，证明N注入具有补偿效应，样片倾向于半绝缘，并未能形成p型Ga2O3薄膜。N离子注入实验虽然并未能得到p型的Ga2O3，但本文对于其掺杂后薄膜特性的探索有利于今后N掺杂Ga2O3绝缘薄膜的应用。
关键词：本征缺陷，禁带宽度，离子注入，载流子浓度，拉曼，结晶质量
注入
II
ABSTRACT
ABSTRACT
Ga2O3 is a wide bandgap semiconductor (~ 4.9 eV) with significant chemical and physical stabilities, which has gained widely interests in recent years. Compared with other wide bandgap semiconductor like SiC and GaN, Ga2O3has higher breakdown voltages and faster electron drift velocity. With these advantages, Ga2O3 has been successively applied for the power devices, such as MESFET, MOSFET and SBD. Besides, it is a promising candidate for use in UV optoelectronic devices, solar cells and so on.The bandgap of Ga2O3 should be tuned to realize high sensitive wavelength-tunable photodetectors. In order to exert the advantage of wide bandgap of gallium oxide effectively at the same time, bandgap tunable films by doping Al were considered. Until now, many experimental studies have been carried out to explore the electrical and optical properties of Al-doped Ga2O3.However, there are few theoretical research about Al-doped Ga2O3.As we all know, intrinsic defects play important roles on the properties of the material and even change the optical and electronic properties of the system.But the Al-doped Ga2O3 with native defects has not been discussed systematically. In addition, due to the presence of intrinsic defects, the development of high-concentration, high-quality p-type Ga2O3 is very difficult. Based on the above two aspects, we have performed systematic studies
on the Al-doped β-Ga2O3 with native defects using density functional theory and conducts an study on the p type-doped Ga2O3 doped with Mg and N. The detailed works are shown as following:
Firstly, the effects of intrinsic defects on the electronic and optical properties of Al-doped β-Ga2O3are investigated with density functional theory. Four types of defect complexes ha ve been considered: Al Ga2O3V O(Al-doped β-Ga2O3 with O vacancy), Al Ga2O3V Ga (Al-doped β-Ga2O3 with Ga vacancy), Al Ga2O3Ga i (Al-doped β-Ga2O3 with Ga interstitial) and Al Ga2O3O i (Al-doped β-Ga2O3 with O interstitial). The calculation results show that the incorporation of Al into β-Ga2O3 leads to the tendency of forming O interstitial defects. And the bandgap of Al Ga2O3is 4.975eV, which is a little larger than that of intrinsic Ga2O3.When O vacancies exist, a defect energy level is introduced to the forbidden band as a deep donor level, while no defective energy levels occur in the forbidden band with O interstitials. After Al-doped, a slightly blue-shift appears in the intrinsic absorption edge, and an additional absorption peak occurs with O vacancy located in 3.69eV.
西安电子科技大学硕士学位论文
Secondly, for the Mg-doped Ga2O3simulation, it was found that a new energy level is introduced to the forbidden band. We predict that this is an acceptor level introduced by Mg. In order to further explore,
we have carried out a corresponding Mg ion implantation experiment and explored the structural characteristics, surface morphology, electrical and optical properties of the Mg-doped Ga2O3 films. After ion implantation, the grain size of the thin film decreases, the Raman peak changes mainly occur in the high frequency region, and a new diffraction peak of MgO2 appears at 45.8°. After annealing, the grain size of each sample becomes larger, the Raman spectrum tends to recover, and the XRD diffraction peaks corresponding to the (402) plane of the Mg1Ga2O3 and Mg3Ga2O3 samples are enhanced. These results show that after annealing, the crystalline quality of the films increases. As the Mg implantation dose increases, the carrier concentration of the film gradually decreases, demonstrating that Mg implantation has a compensating effect and the sample tends to be semi-insulating. Although the Mg ion implantation experiment failed to obtain the p type Ga2O3, the exploration of the properties of the doped thin films in this paper is beneficial to the application of the Mg doped Ga2O3 insulating film in the future.
Finally, we have carried out a N ion implantation experiment and explored the structural characteristics, surface morphology, electrical and optical properties of the N-doped Ga2O3 films. After the ion implantation, Raman peak changes mainly occur in high frequency region. As the implant dose increases, the XPS signal peaks at O1s, Ga3d, and Ga2p shift toward high binding energy side, which
may be due to the formation of GaN. At the maximum implant dose, a new XRD diffraction peak of GaN appeared. Ion implantation makes the surface damaged, the structure appears polycrystalline, and the quality of the crystals decreases. After annealing, the Raman peak near 631.9° has a tendency to recover. The roughness of the samples decreases and the grain size increases. And two new XRD diffraction peaks disappear. These show that after annealing, the crystalline quality of the films is improved. As the N implant dose increases, the material carrier concentration gradually decreases, demonstrating that N implant has a compensating effect and the sample tends to be semi-insulating. Although the N ion implantation experiment failed to obtain the p type Ga2O3, the exploration of the properties of the doped thin films in this paper is beneficial to the application of the N doped Ga2O3 insulating film in the future.
Keywords: intrinsic defects, bandgap, ion Implantation, Raman, carrier concentration, crystal quality
插图索引
插图索引
图1.1Ga2O3的晶胞模型 (2)
图2.1原子力显微镜原理示意图 (9)
图2.2XRD原理图 (10)
图2.3光致发光平台机构示意图 (11)
图3.1Al掺杂1×2×2 Ga2O3超晶胞结合各本征缺陷示意图 (14)
图3.2引入缺陷后Ga2O3和Al Ga2O3体系中各原子位移图 (17)
图3.3引入缺陷后Ga2O3和Al Ga2O3体系中目标原子平均键长变化图 (18)
图3.4(a) Ga2O3 (b) Al Ga2O3 (c) Ga2O3-V O (d) Al Ga2O3V O (e) Ga2O3-O i (f) Al Ga2O3O i 的能带结构图 (19)
图3.5(a) Ga2O3 (b) Al Ga2O3 (c) Ga2O3-V O (d) Al Ga2O3V O (e) Ga2O3-O i (f) Al Ga2O3O i 的态密度图 (20)
图3.6(a) Ga2O3-V O (b) Al Ga2O3V O体系的能带图和分波态密度图 (21)
图3.7各缺陷体系的介电函数虚部图 (23)
图3.8各缺陷体系的吸收谱图 (23)
图4.1(a)本征Ga2O3(b)Mg Ga2O3的能带图 (26)
图4.2Mg-2p态密度图 (26)
图4.3Mg注入氧化镓SRIM仿真结果 (28)
图4.4(a) 退火前后各Mg注入氧化镓样片Raman测试结果(b) 退火前后各Mg注入氧化镓样片高频区Raman测试结果 (29)
图4.5退火前后各Mg注入氧化镓样片XRD扫描结果 (30)
图4.6(a)退火后的各Mg掺杂氧化镓样片XPS全谱(b)O1s峰的XPS谱
(c)Ga3d峰的XPS谱(d)Ga2p峰的XPS谱 (31)
图4.7(a) Undoped Ga2O3 (b) Undoped Ga2O3- N2 (c) Mg2Ga2O3 (d) Mg2 Ga2O3- N2表面形貌图(e) 退火前后各Mg掺杂氧化镓样片的均方根粗糙度 (32)
图4.8Mg2Ga2O3的1/C2-V，I-V与C-V曲线图 (33)
图4.9退火前后后各Mg掺杂氧化镓样片的载流子浓度 (34)
图4.10退火前后Mg掺杂氧化镓各样片的PL谱 (35)
图4.11Mg1Ga2O3样片的PL峰分解图 (35)
图5.1(a)本征Ga2O3(b)N Ga2O3的能带图 (40)
图5.2N注入SRIM仿真结果 (41)
图5.3(a)退火前后各N注入氧化镓样片Raman测试结果(b)退火前后各N注
V

版权声明：本站内容均来自互联网，仅供演示用，请勿用于商业和其他非法用途。如果侵犯了您的权益请与我们联系QQ:729038198，我们将在24小时内删除。