Atomic scale control of the thickness of thin film makes atomic layer deposition highly advantageous in the preparation of high quality super-lattices. However, precisely controlling the film chemical stoichiometry is very challenging. In this study, we deposited SiOx film with different stoichiometry by plasma enhanced atomic layer deposition. After reviewing various deposition parameters like temperature, precursor pulse time, and gas flow, the silicon dioxides of stoichiometric (SiO2) and non-stoichiometric (SiO1.8 and SiO1.6) were successfully fabricated. X-ray photo-electron spectroscopy was first employed to analyze the element content and chemical bonding energy of these films. Then the morphology, structure, composition, and optical characteristics of SiOx film were systematically studied through atomic force microscope, transmission electron microscopy, X-ray reflection, and spectroscopic ellipsometry. The experimental results indicate that both the mass density and refractive index of SiO1.8 and SiO1.6 are less than SiO2 film. The energy band-gap is approved by spectroscopic ellipsometry data and X-ray photo-electron spectroscopy O 1s analysis. The results demonstrate that the energy band-gap decreases as the oxygen concentration decreases in SiOx film. After we obtained the Si-rich silicon oxide film deposition, the SiO1.6/SiO2 super-lattices was fabricated and its photoluminescence (PL) property was characterized by PL spectra. The weak PL intensity gives us greater awareness that more research is needed in order to decrease the x of SiOx film to a larger extent through further optimizing plasma-enhanced atomic layer deposition processes, and hence improve the photoluminescence properties of SiOx/SiO2 super-lattices.

Synchrotron radiation photoelectron spectroscopy combined with scanning electron microscopy ͑SEM͒ and gravimetry has been used to study GaAs ͑100͒ surfaces treated with a neutralized ͑NH 4 ͒ 2 S solution. Compared to the conventional basic ͑NH 4 ͒ 2 S solution treatment, a thick Ga sulfide layer and strong Ga-S bond were formed on the GaAs surface after dipping GaAs wafers in a neutralized ͑NH 4 ͒ 2 S solution. Gravimetric data show that the etching rate of GaAs in the neutralized ͑NH 4 ͒ 2 S solution is about 15% slower than that in the conventional ͑NH 4 ͒ 2 S solution. From SEM observation, fewer etching pits with smaller sizes were found on the neutralized ͑NH 4 ͒ 2 S-treated GaAs surface. © 1997 American Institute of Physics. ͓S0003-6951͑97͒01247-3͔Since Sandroff et al. 1 reported that dipping in a sulfide solution could significantly improve the characteristics of GaAs-based devices, ͑NH 4 ͒ 2 S has attracted much attention and been used frequently for passivating GaAs surfaces. [2][3][4][5][6][7][8][9][10] The passivation has proved effective in that, upon dipping, the surface oxide layer can be thoroughly removed and surface Ga and/or As bonds can be saturated by sulfur atoms, as photoemission data show. 2-10 It is also found that satisfactory passivation may be achieved by using a less basic ͑NH 4 ͒ 2 S x rather than the stoichiometric ͑NH 4 ͒ 2 S solution. 6,8 The basicity of the solution may play some role in the surface sulfuration process. In this letter, we report the passivation of the GaAs ͑100͒ surface using a neutralized ͑NH 4 ͒ 2 S solution instead of the basic one. The experimental results obtained show that, compared to the basic one, the neutralized ͑NH 4 ͒ 2 S solution is a moderate etchant to GaAs and that dipping in such a solution may lead to the formation of a thick passivation layer in which S bonds to Ga strongly.The major experimental technique used in the present work is synchrotron radiation photoemission spectroscopy ͑SRPES͒, which reveals the presence of more chemically shifted Ga 3d and As 3d components than those observed previously. 4 In addition, scanning electron microscopy ͑SEM͒ and gravimetry were used to monitor variations in surface morphology and weight of the sample, respectively.SRPES measurements were carried out at the National Synchrotron Radiation Laboratory, Hefei. Semi-insulating GaAs ͑100͒ single-crystal wafers used in the experiments were ultrasonically cleaned in trichloroethylene, acetone, and ethanol in sequence, etched by 5H 2 SO 4 ϩ1H 2 O 2 ϩ1H 2 O solution for 2 min, and then dipped in fresh-prepared neutralized ͑NH 4 ͒ 2 S solution for about 4 h at room temperature. The neutralized ͑NH 4 ͒ 2 S solution was prepared by dropping dilute HCl ͑about 10% v/v͒ in conventional ͑NH 4 ͒ 2 S solution (pHХ11.5) until the pH value reached 7. After being rinsed with deionized water and dried by flowing nitrogen, the samples were transferred into the SRPES chamber with a base pressure of 2ϫ10 Ϫ8 Pa. A photon energy of 90 eV was used in the measurements of the Ga 3d a...

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The ZnO-based nanogenerators (NGs) with a precisely controlled interlayer of AlN are fabricated based on atomic layer deposition technique, which was proved to possess an enhanced output signal. The microstructure and composition profiles of the prepared ZnO/AlN stack layer are well characterized first. It was found that the piezoelectric performance of ZnO/AlN stacked nanofilm NGs depends strongly on the thickness of AlN. The maximum piezoelectric open circuit output voltage of 4.0 V and output power of 2.42 µW have been achieved with an optimum 2.3 nm thick AlN interlayer. The piezoelectric output of the NGs also relates with the value and the frequency of the compressive force. The inherent mechanism for the improvement of piezoelectric performance in the stacked structure is well discussed. The findings are expected to provide a simple, inexpensive, and effective approach for enhancing the performance of ZnO-based NGs.

A capping layer for black phosphorus (BP) field-effect transistors (FETs) can provide effective isolation from the ambient air; however, this also brings inconvenience to the post-treatment for optimizing devices. We perform low-temperature hydrogenation on Al2O3 capped BP FETs. The hydrogenated BP devices exhibit a pronounced improvement of mobility from 69.6 to 107.7 cm2v−1s−1, and a dramatic decrease of subthreshold swing from 8.4 to 2.6 V/dec. Furthermore, high/low frequency capacitance–voltage measurements suggest reduced interface defects in hydrogenated BP FETs. This could be due to the passivation of interface traps at both Al2O3/BP and BP/SiO2 interfaces with hydrogen revealed by secondary ion mass spectroscopy.