论文标题
朝向光滑（010）β-GA2O3胶片同型通过等离子体辅助分子束外延生长：底物的影响和金属与氧气的磁通量比
Towards smooth (010) beta-Ga2O3 films homoepitaxially grown by plasma assisted molecular beam epitaxy: The impact of substrate offcut and metal-to-oxygen flux ratio
论文作者
论文摘要
光滑的界面和表面对基于薄膜及其异质结构的大多数（Opto）电子设备都是有益的。例如，（010）beta-ga2o3/（alxga1-x）2O3异质结构中的（010）beta-ga2O3/（alxga1-x）的界面更平滑，其粗糙度由GA2O3层的粗糙度统治，可以通过减少界面粗糙度散射来启用更高的迁移率2DEG。为此，我们在实验上证明了沿[001]方向的底物偏外允许在金属富含金属的条件下（010） - 荷马甲基在（010） - homoepitaxy中获得光滑的beta-ga2O3层。在高底物温度（TG = 900°C）下，在分子束外延中施加介导的金属 - 交换催化（MEXCAT），我们比较了（010）面向底物的层形态与不同的无明显外壳的形态。层粗糙度通常由（i）（110）和（-110） - 法统治为沿[001]方向的伸长特征（RMS <0.5 nm），以及（ii）沟槽（5-10 nm深）正交到[001]。我们表明，沿[001]方向几乎仅定向的一个无意的底物几乎仅定向，抑制了这些沟渠，从而形成了光滑的形态，其粗糙度仅由小平面（即rms 0.2 nm）确定。由于我们发现MBE在有和没有Mexcat的MBE生长的层中的相式形态，因此我们提出（010） - 荷马近代的一般增长机制是由岛屿生长统治的，其结合导致沟渠形成。在[001]方向上的底物的存在可以允许在阶跃边缘的阶梯流生长或岛成核，从而阻止了沟槽的形成。此外，我们提供了实验证据，证明表面扩散长度的减小或成核密度的增加，金属与氧的通量比降低。根据我们的结果，我们可以将步骤束排除在MEXCAT期间的沟槽形成的原因以及im依的表面活性剂效应。
Smooth interfaces and surfaces are beneficial for most (opto)electronic devices based on thin films and their heterostructures. For example, smoother interfaces in (010) beta-Ga2O3/(AlxGa1-x)2O3 heterostructures, whose roughness is ruled by that of the Ga2O3 layer, can enable higher mobility 2DEGs by reducing interface roughness scattering. To this end we experimentally prove that a substrate offcut along the [001] direction allows to obtain smooth beta-Ga2O3 layers in (010)-homoepitaxy under metal-rich conditions. Applying In-mediated metal-exchange catalysis (MEXCAT) in molecular beam epitaxy at high substrate temperatures (Tg = 900 °C) we compare the morphology of layers grown on (010)-oriented substrates with different unintentional offcuts. The layer roughness is generally ruled by (i) (110) and (-110)-facets visible as elongated features along the [001] direction (rms < 0.5 nm), and (ii) trenches (5-10 nm deep) orthogonal to [001]. We show that an unintentional substrate offcut of only 0.1° almost oriented along the [001] direction suppresses these trenches resulting in a smooth morphology with a roughness exclusively determined by the facets, i.e., rms 0.2 nm. Since we found the facet-and-trench morphology in layers grown by MBE with and without MEXCAT, we propose that the general growth mechanism for (010)-homoepitaxy is ruled by island growth whose coalescence results in the formation of the trenches. The presence of a substrate offcut in the [001] direction can allow for step-flow growth or island nucleation at the step edges, which prevents the formation of trenches. Moreover, we give experimental evidence for a decreasing surface diffusion length or increasing nucleation density with decreasing metal-to-oxygen flux ratio. Based on our results we can rule-out step bunching as cause of the trench formation as well as a surfactant-effect of indium during MEXCAT.
