GaN钝化层在GaInP异质界面上的光电子能谱研究与能带对齐
Photoemission study and band alignment of GaN passivation layers on GaInP heterointerface
AI总结：
本研究通过X射线和紫外光电子能谱分析了GaInP上GaN钝化层的能带对齐，发现其能显著减少表面态并提高PEC器件稳定性。
摘要：
基于III-V族半导体的光电化学（PEC）器件展现出最高的太阳能转电能或太阳能转燃料效率。由于其可调的晶格常数、电子能带结构和优异的光学性质，GaInP是用于集成和直接太阳能燃料生产的PEC中相关顶部光吸收层或电荷选择性接触层。为了增强其表面抵抗导致分解的化学腐蚀的稳定性，我们沉积了GaN保护和钝化层。n掺杂的GaInP(100)外延层通过金属有机化学气相沉积在GaAs(100)衬底上生长。随后，通过原子层沉积在氧化的GaInP表面上生长了1-20 nm的薄GaN薄膜。我们通过X射线和紫外光电子能谱研究了这些多结异质结构的能带对齐。由于光电子的发射深度有限，我们通过一系列独立的测量来确定能带对齐，在这些测量中，我们要么改变GaInP(100)的表面终止，要么改变在GaInP(100)缓冲层上生长的GaN薄膜厚度。在用众所周知的富磷(2x2)/c(4x2)重构制备的n-GaInP(100)表面上，我们发现了0.34 eV的向上表面能带弯曲（BB），以及由于现有表面态导致的费米能级钉扎。氧化后，表面态被部分钝化，导致BB降至0.12 eV，且GaInP与氧化物能带之间的价带偏移（VBO）为2.0 eV。在GaInP(100)缓冲层和GaN钝化层之间，我们确定了1.8 eV的VBO。发现的相应导带偏移为-0.2 eV，相当小。因此，我们评估认为应用GaN钝化层是一项极具前景的技术步骤，不仅能减少表面态，还能提高光电化学器件表面的稳定性。
英文摘要：
III-V semiconductor-based photoelectrochemical (PEC) devices show the highest solar-to-electricity or solar-to-fuel conversion efficiencies. GaInP is a relevant top photoabsorber layer or a charge-selective contact in PEC for integrated and direct solar fuel production, due to its tunable lattice constant, electronic band structure, and favorable optical properties. To enhance the stability of its surface against chemical corrosion which leads to decomposition, we deposit a GaN protection and passivation layer. The n-doped GaInP(100) epitaxial layers were grown by metalorganic chemical vapor deposition on top of GaAs(100) substrate. Subsequently, thin 1-20 nm GaN films were grown on top of the oxidized GaInP surfaces by atomic layer deposition. We studied the band alignment of these multi-junction heterostructures by X-ray and ultraviolet photoelectron spectroscopy. Due to the limited emission depth of photoelectrons, we determined the band alignment by a series of separate measurements in which we either modified the GaInP(100) surface termination or the film thickness of the grown GaN on GaInP(100) buffer layers. On n-GaInP(100) surfaces prepared with the well-known phosphorus-rich (2x2)/c(4x2) reconstruction we found up-ward surface band bending (BB) of 0.34 eV, and Fermi level pinning due to the present surface states. Upon oxidation, the surface states are partially passivated resulting in a reduction of BB to 0.12 eV and a valence band offset (VBO) between GaInP and oxide bands of 2.0 eV. Between the GaInP(100) buffer layer and the GaN passivation layer, we identified a VBO of 1.8 eV. The corresponding conduction band offset of -0.2 eV is found to be rather small. Therefore, we evaluate the application of the GaN passivation layer as a promising technological step not only to reduce surface states but also to increase the stability of the surfaces of photoelectrochemical devices.
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