Surface treatments toward obtaining clean GaN(0001) from commercial hydride vapor phase epitaxy and metal-organic chemical vapor deposition substrates in ultrahigh vacuum
Surface treatments toward obtaining clean GaN(0001) from commercial hydride vapor phase epitaxy and metal-organic chemical vapor deposition substrates in ultrahigh vacuum
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DOI：
10.1016/j.apsusc.2010.03.001
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发表时间：
2010-05-01
影响因子：
6.7
通讯作者：
Daimon, Hiroshi
中科院分区：
文献类型：
--
作者：
Hattori, Azusa N.;Endo, Katsuyoshi;Daimon, Hiroshi
我们研究了在四种不同类型的硅片上清洗GaN（0 0 0 1）表面的工艺：两种类型是氢化物气相外延（HVPE）独立衬底，两种类型是在这些HVPE衬底上生长的金属有机化学气相沉积（MOCVD）薄膜，通过退火和/或在超高真空中氩离子溅射制备。我们通过原位低能电子衍射（LEED）、反射高能电子衍射（RHEED）、扫描隧道显微镜（STM）和俄格电子能谱，以及非原位温度程序解吸、x射线光电子能谱、x射线衍射和二次离子质谱对表面进行了观察。对于HVPE样品，我们在优化的三步退火条件下（200℃12 h + 400℃1 h + 500℃5 min）获得了相对清洁的表面，没有溅射，之后表面氧化物和碳化物的污染减少到退火前的20%左右。通过LEED和RHEED获得清晰的GaN(0 0 0 1)1 x 1模式。STM图像显示10 nm大小的平坦梯田和0.5 nm高度的台阶。在更高的温度（550℃）下退火hpe - gan样品后，形成了具有面的三维（3D）岛，并且由于样品中含有氢作为杂质，氮以氨的形式解吸，表面化学量被分解。Ar+溅射能有效去除表面污染，但后镀不能恢复表面粗糙度，反而会促进表面三维岛屿的形成。对于MOCVD/HVPE同外延样品，表面被氢终止，引入样品显示出清晰的1 × 1结构。在500-600℃退火后，表面氢被去除，部分出现3 × 3的重构结构，但1 × 1结构占主导地位。我们总结了相同处理下样品的结构差异，并阐明了晶体质量（如位错、氢杂质浓度和GaN膜中残留的反应物分子）对表面结构的影响。(C) 2010 Elsevier B.V.版权所有
We studied processes of cleaning GaN(0 0 0 1) surfaces on four different types of wafers: two types were hydride vapor phase epitaxy (HVPE) free-standing substrates and two types were metal-organic chemical vapor deposition(MOCVD) films grown on these HVPE substrates and prepared by annealing and/or Ar ion sputtering in ultra high vacuum. We observed the surfaces through treatments using in situ low-energy electron diffraction (LEED), reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM), and Auger electron spectroscopy, and also using ex situ temperature programmed desorption, X-ray photoelectron spectroscopy, X-ray diffraction, and secondary ion mass spectrometry. For HVPE samples, we obtained relatively clean surfaces under optimized three-step annealing conditions (200 degrees C for 12 h + 400 degrees C for 1 h + 500 degrees C for 5 min) without sputtering, after which the surface contamination of oxide and carbide was reduced to similar to 20% of that before annealing. Clear GaN(0 0 0 1)1 x 1 patterns were obtained by LEED and RHEED. STM images showed flat terraces of similar to 10 nm size and steps of similar to 0.5 nm height. Upon annealing the HVPE-GaN samples at a much higher temperature (> 550 degrees C), three-dimensional (3D) islands with facets were formed and the surface stoichiometry was broken down with the desorption of nitrogen in the form of ammonia, since the samples include hydrogen as an impurity. Ar+ sputtering was effective for removing surface contamination, however, postannealing could not recover the surface roughness but promoted the formation of 3D islands on the surface. For MOCVD/HVPE homoepitaxial samples, the surfaces are terminated by hydrogen and the as-introduced samples showed a clear 1 x 1 structure. Upon annealing at 500-600 degrees C, the surface hydrogen was removed and a 3 x 3 reconstruction structure partially appeared, although a 1 x 1 structure was dominant. We summarize the structure differences among the samples under the same treatment and clarify the effect of crystal quality, such as dislocations, the concentration of hydrogen impurities, and the residual reactant molecules in GaN films, on the surface structure. (C) 2010 Elsevier B.V. All rights reserved.