摘要
摘要
32O Ga -β是一种新型宽禁带氧化物半导体材料，禁带宽度大约为4.9eV ，具有良好的化学和热稳定性，在紫外探测器、功率器件等领域应用前景广阔。由于蓝宝石与氧化镓的晶格常数、热膨胀系数不同，外延薄膜中存在大量的点缺陷、位错等，直接影响到后期制备器件的工作效率和可靠性。本文采用在蓝宝石(0006)晶面上外延的32O Ga -β和32x -1x O )Ga Al -（β薄膜进行退火实验，研究了退火气氛、温度、时间等退火工艺参数对薄膜结晶质量、光学特性、表面组分等特性的影响。同时，在氧化镓薄膜上制备了紫外日盲探测器，对比分析了在不同气氛中退火的薄膜上制备的探测器的性能及其微观机理。共得到如下结论：过氧化锰
第一，700C 条件下，随着退火时间的增长，晶体择优取向变好，表面平整度基本不变，吸收带边持续蓝移，光学带隙变大。900C 条件下，衍射峰峰位随退火时间延长向小角度偏移，这是因为较高的退火温度引入的应力使得晶体内部发生了晶格畸变，且应力对于晶格常数的贡献大于高温衬底互扩散的贡献。而1000C 条件下，铝镓氧的衍射峰先是在6h 时向小角度移动，然后随着退火时间的增长向大角度方向移动，这是因为较高的退火温度加上较长的退火时间使得衬底Al 原子向外延膜的扩散已经充分进行。对于光学特性，随着退火时间的增加，薄膜的透过率均先增高后降低，这与薄膜表面粗糙度变化规律一致。
第二，800C 下对不同气氛中退火的氧化镓薄膜的研究发现，退火气氛对氧化镓的晶体结构影响整体上不明显，相比较而言，氮气退火效果较好。对于表面形貌，退火后，薄膜表面小晶峰大量减小，粗糙度降低，平整度明显改善。对于透射谱，氮气和空气中退火的样品光学带隙有所增加。氧气中的薄膜的吸收带边则轻微红移，这可能是因为氧气气氛给薄膜引入了较多的间隙原子，形成了点缺陷，而缺陷能级吸收较低频率的光。
第三，探测器的I-V 曲线显示，氮气气氛中退火的样品制备的器件的光电流最大，其他气氛中退火后的电流则比参考片弱，因为结晶质量较高的晶体更有利于载流子的迁移，电导更大。对于时间响应，退火处理后，探测器的上升时间和下降时间都明显减少，且氧气中退火的样品最短。这是因为氧气中退火的薄膜内部的氧空位最少，降低了薄膜表面的自由电子数目，从而降低氧原子吸附和电离对探测器时间响应的影响。因此，实际工艺流程中，应根据器件性能需求选择合适的退火气氛。
第四，铝镓氧薄膜退火研究结果发现，800C 条件下后，氮气中退火的样品结晶质量明显改善，氧气和空气中变化不明显，吸收带边无明显变化，800C 退火后表面粗糙度则有所增加。而1000C 退火后，XRD 结果表明退火对铝镓氧薄膜质量有明显
的改善作用，同时，吸收带边出现明显蓝移，薄膜均方根粗糙度则明显降低，且均以氮气中退火效果
最好。XPS分析结果显示，退火前薄膜处于缺氧状态，薄膜中Ga以Ga3+为主，同时存在Ga2+等低价镓离子。1000C 退火后氧组分明显提高，可能是气氛中氧原子进入晶格，氧空位减少所致。同时，退火后Ga3d和O1s信号峰分析表明，其结合能都有所增大，半高宽明显降低，峰强也有所增强，这说明Ga-O或者Al-O 键的键能在退火之后增加，成键质量提高，且氧气中退火的最好。对N1s信号峰的分析显示，退火之后引入了新的杂质氮原子。
关键词：氧化镓，宽禁带，退火，光电探测器
ABSTRACT
ABSTRACT
32O Ga -β is a new wide bandgap oxide semiconductor material with good chemical and thermal stability, whose bandgap is about 4.9 eV , Hence, 32O Ga -β can be widely used in ultraviolet photodetector, power devices and so on. However, lattice mismatch and thermal mismatch between substrate and epitaxial layer cause lots of point defects, dislocation and so on, which are closely related with decives ’work efficiency and reliability.
In this paper, As-grown 32O Ga -βand 32x -1x O )Ga Al -（
皮衣加工
β samples were annealed at different temperature, ambient and duration. And the effect of these parameters on crystal quality, surface morphology, optical property, surface chemical composition and chemical state were studied. In addition, solar-blind ultraviolet detectors were fabricated on 32O Ga -β films, the influence of annealing ambient on the detectors ’ performance and the micromechanism were studied. The details work are as follows.
Firstly, under the annealing temperature of 700 degree centigrade, as the duration of annealing grows, the films ’crystal preferred orientation improved. the films ’ roughness remain unchanged. the absorption edge shift towards the blue end of the spectrum.and optial bandgap increased. When annealing temperature reaches 900 degree centigrade, the diffraction peak move to small angle, This is because the stress introduced by high annealing temperature lead to lattice distortion, and its contribution to lattice is larger than interdiffusion. When annealing temperature increase up to 1000 degree centigrade, the peak diffraction peak shift towards small angle first and then shift towards large angle, this is because high temperature and annealing duration has promoted interdiffusion greatly. For optical characteristic, as the duration of annealing grows, the transmittance increased firstly and then decreased, this is in accord with the results of films ’ surface morphology.
Secondly, for the films annealed in different ambient, annealing ambient has little effect on the crystal
structure of 32O Ga -β under the annealing temperature of 800 degree centigrade, and nitrogen has the relatively better consequence. For surface morphology, surface smoothness improved. For the transmission spectrum, the absorption edge of the films annealed in nitrogen and air shift towards the blue end of the spectrum slightly. The bandgap increased as well. For the film annealed in oxygen, the absorption edge shift towards the red end of the spectrum slightly. This is because oxygen introduced interstitial atoms, and these defect level will absorb low frequency light. Thirdly, the I-V curves of photodetectors show that the detector prepared on the film
annealed in nitrogen has the maximal photocurrent. The photocurrent of samples annealed in air and oxygen is smaller than reference, because the better the crystal quality is, the easier the carriers move and the bigger the conductance is. On the contrary, deteriorated samples can scattering the carriers and result in smaller photocurrent. For the time response, the rise time and fall time both decreased after annealing. And the detector prepared on film annealed in oxygen has the shortest fall time, because the films annealed in oxygen has the least oxygen vacancy. And the number of free electrons on the film ’s surface decreased. So the effects of oxygen adsorption and ionization is weaken. Therefore, we should choose the reasonable annealing condition according to the requirem
ents of devices.
Finally, For 32x -1x O Ga Al -）（β films, under the annealing temperature of 800 degree
centigrade, the diffraction peak shift towards to small angle slightly. And the peak intensity of the film annealed in nitrogen is strongest. Other samples almostly remain unchanged. the absorption edge and bandgap almost keep unchanged. Under the annealing temperature of 1000 degree centigrade, results show that annealing has a good influence on 32x -1x O Ga Al -）（βfilms. And nitrogen is the best atmosphere for improving film ’s crystal quality. Meanwhile, the absorption edge shift towards to blue end of the spectrum and optical bandgap increased. the RMS roughness increased slightly. The results of XPS reveal that the films are oxygen deficient. The Ga in films exists in +3Ga , +2Ga , +Ga form. The amount of oxygen increased after annealed, this is because oxygen entered lattice and oxygen vacancy decreased. Meanwhile, the binding energy of Ga3d and O1s increased after annealing, the full width at half maximum deceased obviously. and the peak intensity is stronger. The results prove that the energy of Ga-O and Al-O increased and the quality of chemical bond improved. The signal peaks of N1s reveal that new nitrogen was introduced after annealing.
Keywords : Gallium oxide, wide bandgap, annealing, photodetector
插图索引
炫轮
插图索引
图1.1 氧化镓的同分异构体向β型的转化方法(a)与32O Ga -β的晶胞结构[7](b) . 1 图2.1
贝意克箱式炉(a)与管式炉(b)...................................................................... 7 图2.2
氧化镓基紫外探测器的版图(a)与结构图(b)............................................ 10 图3.1
退火温度程序曲线（以空气中在1000C 下退火1小时为例） .......... 14 图3.2
氧化镓薄膜在700C 条件下空气中退火不同时间的XRD 图谱 .......... 15 图3.3rbd-508
氧化镓薄膜700C 下在空气中退火不同时间的）（036峰位的对比 ...... 15 图3.4
饮用水过滤器氧化镓薄膜在900C 条件下空气中退火不同时间的XRD 图谱 .......... 16 图3.5
氧化镓薄膜900C 下在空气中退火不同时间的）（036峰位的对比 ...... 17 图3.6
氧化镓薄膜1000C 下在空气中退火不同时间的）（036峰位对比 ........ 18 图3.7
氧化镓薄膜1000C 条件下在空气中退火不同时间的XRD 图谱 ........ 18 图3.8
在700C 下不同退火时间的透射谱 ........................................................ 20 图3.9 在900C 下不同退火时间的透射谱 ........................................................ 20 图3.10 1000C 下不同退火时间的透射谱 .. (21)
图3.11 700C 退火后薄膜的2h ）（να~h ν曲线 (21)
铜管焊接
图3.12 900C 退火后薄膜的2h ）
（να~h ν曲线 .................................................... 22 图3.13 1000C 退火后薄膜的2h ）（να~h ν曲线 .. (22)
图3.14 700C 下不同时间退火后薄膜的表面形貌 ............................................. 24 图3.15 900C 下不同退火时间下氧化镓的表面形貌图 ..................................... 24 图3.16 1000C 下不同退火时间下的氧化镓的表面形貌 ................................... 25 图3.17 不同温度下退火的薄膜的XRD 衍射谱 .................................................. 26 图3.18 氧化镓薄膜在空气中退火不同时间的）
（036峰位的对比 ...................... 26 图3.19 不同温度下退火的薄膜的透射谱和吸收谱 (27)
图3.20 退火前后薄膜的2h ）（να~h ν曲线 (27)
图3.21 不同温度退火后薄膜的表面形貌 ............................................................. 28 图3.22 不同气氛中退火的氧化镓薄膜的XRD 图谱 .......................................... 29 图3.23 不同气氛中退火后)036(峰位的对比图 ................................................... 30 图3.24 不同气氛中退火的氧化镓薄膜的透射谱 . (31)
图3.25 不同气氛中退火后薄膜的2h ）（να~h ν曲线 (31)
图3.26 不同气氛中退火后的氧化镓薄膜的表面形貌 ......................................... 32 图3.27 不同的光照功率下，在不同气氛中退火的氧化镓薄膜上制备的探测器
的光电流对比 (33)
