GaAs衬底上等离子体增强原子层沉积GaN薄膜*

Plasma-enhanced atomic layer deposition of GaN thin films on GaAs substrate*

摘要:

采用等离子体增强原子层沉积(PEALD)技术在斜切的砷化镓(GaAs)衬底上低温沉积了氮化镓(GaN)薄膜，对生长过程、表面机制以及界面特性等进行分析，得到GaN在215~270℃的温度窗口内GPC(growth-per-cycle)为0.82?/cycle，并从表面反应动力学和热力学方面对GPC的变化进行了分析。研究发现，生长的GaN薄膜为多晶，具有六方纤锌矿结构，且出现(103)结晶取向。在GaN/GaAs界面处观察到约1nm厚的非晶层，可能与生长前衬底表面活性位点的限制和前驱体的空间位阻效应有关。更为有意思的是，在沉积的GaN薄膜中，所有的N皆与Ga以Ga-N键结合生成GaN，但是存在少部分Ga形成了Ga-O键和Ga-Ga键。这种沉积时的成键方式，可能与GaN薄膜中存在的缺陷和杂质有关。

Abstract:

Polycrystalline gallium nitride (GaN) thin films were deposited at low temperatures on GaAs (001) substrates via plasma-enhanced atomic layer deposition (PEALD). The growth process, surface mechanism and interface characteristics were investigated. The results showed that the PEALD temperature window was 215~270℃, and the average growth rate of GaN thin films was 0.82?/cycle. The GPC analysis was performed in terms of kinetic energy barriers and thermodynamics. X-ray diffraction (XRD) patterns indicate that the GaN thin films are polycrystalline with hexagonal wurtzite structure and have a tendency to form (103) preferential orientation. With High-resolution transmission electron microscopy (HRTEM), the atomic steps on the mitered substrate surface and the presence of an amorphous layer of about 1 nm at the GaN/GaAs interface are easily observed. This may be related to the surface concentration of active sites and the steric effect of the adsorbed precursor fragments. Most interestingly, X-ray photoelectron spectroscopy (XPS) analysis shown that all N elements combine with Ga elements to form GaN by Ga-N bond, but a small part of Ga formed Ga-Ga bonds and Ga-O bonds. This bonding method during deposition may be related to the defects and impurities in the GaN thin films.