Formation Of nc-Si Research Articles

Formation of Si:H:Cl Films at Low Temperatures of 90–140°C by RF Plasma-Enhanced Chemical Vapor Deposition of a SiH2Cl2 and H2 Mixture

The role of chlorine in the formation of chlorinated hydrogenated silicon (Si:H:Cl) films is investigated through film depositions at low temperatures of 90–140°C by rf (13.56 MHz) plasma-enhanced chemical vapor deposition (PE-CVD) of a dichlorosilane SiH2Cl2 and H2 mixture. There exists the threshold substrate temperature of ∼110°C for phase transition from polysilane/siloxene to nanocrystalline Si (nc-Si), which is ruled by the chemical reactivity of the deposition precursor, SiHxCly (x+y<3) on the growing surface. The Si:H:Cl films deposited at substrate temperature Ts below 110°C have polysilane/siloxene structure and they show relatively strong photoluminesence in the visible region of 600–800 nm. On the other hand, most of the chlorine atoms are consumed to release the hydrogen from the growing surface at Ts above 110°C, resulting in the nc-Si formation. This difference is determined by the surface reaction during film growth.

FORMATION OF SILICON NANOCRYSTALS AND INTERFACE ISLANDS IN SYNCHROTRON-RADIATION-IRRADIATED SiO2 FILMS ON Si(100)

Nucleation of nanocrystalline Si (nc-Si) in SiO 2 films irradiated with vacuum ultraviolet and soft x-ray radiation has been investigated by using in-situ spectroscopic ellipsometry, cross-sectional transmission electron microscopy, reflectivity measurement, and reflection high-energy electron diffraction. The formation of nc-Si proceeds in the repetition of two steps: (i) conversion of SiO 2 to SiO x through the creation of Frenkel pairs and the subsequent desorption of O 2, and (ii) separation of SiO x into Si and SiO 2 domains. The average diameter of nc-Si increases from 2 to 10 nm as the irradiation temperature increases from 470°C to 610°C. Above 700°C, oxide domains are gone and solid-phase recrystallization produces Si islands terminated by the Si(100) substrate interface. At temperatures higher than 800°C, these islands collapse and an atomically flat Si(100) interface appears.

Deposition of nanocrystalline silicon mediated by ultrathin aluminum underlayers by PCVD and sputter-deposition at 500 K

Silicon layers were deposited by standard PCVD from undiluted silane or sputter-deposition, respectively, onto aluminum underlayers of 4–32 nm thickness. Above a critical thickness of the Al-layer around 8 nm, the growth of nanocrystalline silicon is observed. The intentional introduction of hydrogen into the sputter-deposited bilayers showed a weak effect on crystallite formation. In contrast, the argon pressure during Si-sputtering was found to strongly affect the formation of nc-Si. Effective growth of Si-crystallites is accompanied by a consumption of Al from the underlayer and an increased diffusion of Al into the silicon as detected by X-ray methods and concentration in-depth profiles, respectively. As found by atomic force microscopy, the typical rough surface of the Al-underlayers is preserved during the growth of the Si-overlayers. The effect of the aluminum-mediated growth is explained by a migration of Al-crystallites from the underlayer into the growing film.

Formation of Silicon Nanocrystallites by Electron Cyclotron Resonance Chemical Vapor Deposition and Ion Beam Assisted Electron Beam Deposition

AbstractNano-crystalline silicon (nc-Si) thin films were directly deposited by electron cyclotron resonance chemical vapor deposition (ECR-CVD) and ion beam assisted electron beam deposition (IBAED) method. In the sample deposited by ECR-CVD, the room temperature photoluminescence originated from the nc-Si and the silicon-hydrogen bond were appeared. It was confirmed that the size of the nc-Si could be controlled up to about 3 nm with the low substrate temperature during the deposition process and then the hydrogen atoms play a very important role in the formation of the nc-Si. The IBAED method was also found to an useful technique for nc-Si formation by the control of ion beam power.

The effect of hydrogen species on the electronic properties of nc-Si:H prepared in a triode PECVD system

The effect of hydrogen species on the microstructures and the electronic properties of nanometer sized crystalline silicon (nc-Si:H) prepared in a triode plasma-enhanced chemical vapor deposition (PECVD) system with a hydrogen-diluted silane plasma were investigated. It has been found that for a given set of deposition parameters there is a threshold value of dilution ratio ( H 2 H 2 + SiH 4 ) for the formation of nc-Si:H, which suggests that a minimum concentration of hydrogen atoms should be provided at the growing surface during the deposition processes. The electronic properties of nc-Si:H were changed when the H 2 dilution ratio was greater than 94%. The dark-conductivity, σ d, increased from 10 −10 to 10 −3 S/cm, although the photo-conductivity, σ ph, changed by only one order of magnitude. In addition, the drift mobility, μ d, increased from 0.8 to 16 cm 2/V · s. The dependence of the electronic properties on the hydrogen content and structural configurations in nc-Si:H is briefly discussed.