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首页> 外文期刊>Physical Review, B. Condensed Matter >Control of crystal polarity in a wurtzite crystal: ZnO films grown by plasma-assisted molecular-beam epitaxy on GaN - art. no. 115331
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Control of crystal polarity in a wurtzite crystal: ZnO films grown by plasma-assisted molecular-beam epitaxy on GaN - art. no. 115331

机译：控制纤锌矿晶体中的晶体极性：通过等离子辅助分子束外延在GaN上生长的ZnO薄膜-art。没有。 115331

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ZnO/GaN heterointerfaces are engineered to control the polarity of ZnO films grown by plasma-assisted molecular beam epitaxy on Ga-polar GaN templates. The polarity of ZnO films is determined both by coaxial impact collision ion scattering spectroscopy (CAICISS) and by convergent beam electron diffraction (CBED). Polarity inversion can be achieved by inserting an interface layer with a center of symmetry, because the polarity comes from a lack of the center of symmetry. An O-polar (anion-polar) ZnO film can be grown on Ga-polar (cation-polar) GaN by inserting a Ga2O3 layer at the interface, while Zn-polar ZnO is grown on GaN without forming an interface layer. A single-crystalline monoclinic Ga2O3 layer, which has a center of symmetry, is formed by O-plasma preexposure on the Ga-polar GaN surface prior to ZnO growth, while the ZnO/GaN interface without any extra layer is formed by Zn preexposure. The orientation relationship between ZnO, Ga2O3, and GaN is determined as [2-1-10]ZnOparallel to[010](Ga2O3)parallel to[2-1-10](GaN) and (0001)(ZnO)parallel to(001)(Ga2O3)parallel to(0001)(GaN). The CAICISS results reveal the growth of an O-polar ZnO film on O-plasma-preexposed GaN, while a Zn-polar ZnO film on Zn-preexposed GaN. The origin of the observed features in polar-angle-dependent CAICISS spectra can be analyzed by considering the shadow cones of Zn and O atoms formed by incident ions and shadowing and focusing effects of scattered ions. Azimuthal-angle-dependent CAICISS spectra reveal the surfaces of both Zn- and O-polar ZnO films as mixture of c and c/2 planes with a ratio of about 50:50. The ZnO film with a Ga2O3 interface layer shows a degradation in the crystal quality as evidenced by a broadening of the x-ray rocking curves. The CBED results for the O-plasma-preexposed samples reveal Ga-polar GaN and O-polar ZnO for the O-plasma-preexposed samples, which directly confirms polarity inversion from cation to anion polar. On the other hand, Zn- polar ZnO CBED patterns are obtained from ZnO films grown on Zn- preexposed Ga-polar GaN, which indicates the same cation polarity for a ZnO/GaN interface without the formation of an interface layer. It is noted that no planar or faceted inversion domain boundaries are formed to invert the polarity (from Ga polar to O polar). This indicates that we can control the polarity by engineering interfaces. [References: 27]
机译：ZnO / GaN异质界面经设计可控制通过Ga-polar GaN模板上的等离子体辅助分子束外延生长的ZnO薄膜的极性。 ZnO薄膜的极性通过同轴碰撞碰撞离子散射光谱法（CAICISS）和会聚束电子衍射法（CBED）确定。极性反转可通过插入具有对称中心的界面层来实现，因为极性来自缺乏对称中心。通过在界面上插入Ga2O3层，可以在Ga极性（阳离子极性）GaN上生长O极性（阴离子极性）ZnO膜，而在GaN上生长Zn-极性ZnO而不形成界面层。在ZnO生长之前，通过在Ga极性GaN表面上进行O-等离子预曝光，形成具有对称中心的单晶Ga2O3单晶层，而通过Zn预曝光形成没有任何额外层的ZnO / GaN界面。 ZnO，Ga2O3和GaN之间的取向关系确定为平行于[2-1-10]（GaN）的[2-1-10] ZnO和平行于[2-1-10]（GaN）的（0001）（ZnO） 001）（Ga2O3）平行于（0001）（GaN）。 CAICISS结果显示，在预暴露O等离子体的GaN上生长O极性ZnO膜，而在预暴露Zn的GaN上生长Zn极性ZnO膜。可以通过考虑入射离子形成的Zn和O原子的阴影锥以及散射离子的阴影和聚焦效应，来分析与极角相关的CAICISS光谱中观察到的特征的起源。依赖于方位角的CAICISS光谱揭示了Zn和O极性ZnO薄膜的表面是c和c / 2平面的混合物，比例约为50:50。 X射线摇摆曲线变宽可以证明具有Ga2O3界面层的ZnO膜的晶体质量下降。 O-等离子体暴露样品的CBED结果显示，O-等离子体暴露样品的Ga-极性GaN和O-极性ZnO，直接证实了从阳离子极性转变为阴离子极性的极性。另一方面，从在预先暴露于Zn的Ga极性GaN上生长的ZnO薄膜获得Zn极性ZnO CBED图案，这表明ZnO / GaN界面具有相同的阳离子极性，而没有形成界面层。注意，没有形成平面或多面的反转域边界以反转极性（从Ga极性到O极性）。这表明我们可以通过工程接口控制极性。 [参考：27]

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