Fu Zhu-Xi

Photoluminescent Properties of ZnO Films Deposited on Si Substrates

The photoluminescence of ZnO films deposited on Si substrates by reactive dc sputtering has been studied by using a synchrotron radiation (SR) light source. The excitation spectra show a strong excitation band around 195 nm related to the 390 nm emission band. Under SR vacuum ultraviolet excitation, a new emission band peaked at 290 nm was found for the first time, besides the ultraviolet emission band (390 nm) and green band (520 nm).

Effect of Ag Doping on Optical and Electrical Properties of ZnO Thin Films

ZnO thin films were prepared on p-type Si (100) substrates by the sol-gel process. The influence of Ag doping at a content of 0.002 % on the photoluminescence and current-voltage (I−V) characteristics of ZnO thin films has been investigated. It is found that Ag doping leads to a pronounced increase in the intensity of near band edge emission at 3.23 eV and a remarkable red shift of the visible broadband at room temperature. The I−V characteristics of ZnO/p-Si heterojunctions are also changed. These results could be explained by Ag substituting for Zn in Ag doped ZnO thin films.

Dependence of Photovoltaic Property of ZnO/Si Heterojunction Solar Cell on Thickness of ZnO Films

N-ZnO/p-Si heterojunctions are prepared by sputtering deposition of intrinsic ZnO films on p-Si substrates. Thicknesses of ZnO films are altered by varying the deposition time from 1 h to 3 h. The electrical properties of these structures are analysed from capacitance-voltage (C-V) and current-voltage (I-V) characteristics performed in a dark room. The results demonstrated that all the samples show strong rectifying behaviour. Photovoltaic property for the samples with different thicknesses of ZnO films are investigated by measuring open circuit voltage and short circuit current. It is found that photovoltages are kept to be almost constant of 320 mV along with the thickness while photocurrents changing a lot. The variation mechanism of the photovoltaic effect as a function of thickness of ZnO films is investigated.

Electrical and deep levels characteristics of ZnO/Si heterostructure by MOCVD deposition

ZnO films have been prepared on p-type Si substrates by metal-organic chemical vapour deposition (MOCVD) at different total gas flow rates. The current versus voltage and temperature (I – V – T) characteristics, the deep-level transient spectroscopy (DLTS) and the photoluminescence (PL) spectra of the samples were measured. DLTS shows two deep-level centres of E1 (EC-0.13±0.02eV) and E2 (EC-0.43±0.05eV) in sample 1202a, which has a ZnO/p-Si heterostructure. A deep level at EC-0.13±0.01eV was also obtained from the I – T characteristics. It was considered to be the same as E1 obtained from DLTS measurement. The emission related to this deep level center was detected by PL spectra. In addition, the energy location and the relative trap density of E1 was varied when the total gas flow rate was changed.

Photoelectric conversion characteristics of ZnO/SiC/Si heterojunctions

A series of n-ZnO/n-SiC/p-Si and n-ZnO/p-Si heterojunctions were prepared by DC sputtering. Their structural properties, I—V curves, photovoltaic effects and photo-response spectra were studied. The photoelectric conversion characteristics of n-ZnO/n-SiC/p-Si and n-ZnO/p-Si heterojunctions were investigated. It is found that the photoelectric conversion efficiency of the n-ZnO/n-SiC/p-Si heterojunction is about four times higher than that of the n-ZnO/p-Si heterojunction. The photovoltaic response spectrum indicated that the photoresponse curve of n-ZnO/n-SiC/p-Si increased more strongly than that of n-ZnO/p-Si with the wavelength increasing. It shows that the photoresponse of n-ZnO/p-Si can be enhanced when inserting a 3C-SiC layer between ZnO and Si. There is one inflexion in the photocurrent response curve of the n-ZnO/p-Si heterojunction and two inflexions in that of the n-ZnO/n-SiC/p-Si heterojunction. It is clear that the 3C-SiC plays an important role in the photoelectric conversion of the n-ZnO/n-SiC/p-Si heterojunction.

Influence of Interface Charge on Electrical Properties of ZnO/Si Heterojunction

The capacitance?voltage and current?voltage properties of the samples before and after annealing are investigated at 300?K and 195?K. It is found that the interface charge plays an important role for the heterojunction properties. After annealing, the samples exhibit typical junction properties. The heterojunction shows a built-in potential 0.62?eV consistent with the theoretical result 0.67?eV. However, the sample exhibits more complex behaviour before annealing. The experimental results can be explained by heterojunction theory when introducing interface charge, which suggests that the annealing can reduce interface charge and can improve the junction properties of the samples.

Effect of Annealing Temperature on Structural and Optical Properties of N-Doped ZnO Films

Nitrogen-doped ZnO (ZnO:N) films are prepared by thermal oxidation of sputtered Zn3N2 layers on Al2O3 substrates. The correlation between the structural and optical properties of ZnO:N films and annealing temperatures is investigated. X-ray diffraction result demonstrates that the as-sputtered Zn3N2 films are transformed into ZnO:N films after annealing above 600° C. X-ray photoelectron spectroscopy reveals that nitrogen has two chemical states in the ZnO:N films: the NO acceptor and the double donor (N2)O. Due to the No acceptor, the hole concentration in the film annealed at 700° C is predicted to be highest, which is also confirmed by Hall effect measurement. In addition, the temperature dependent photoluminescence spectra allow to calculate the nitrogen acceptor binding energy.

Structural and Luminescent Properties of ZnO Thin Films Deposited by Atmospheric Pressure Chemical Vapour Deposition

ZnO thin films were successfully deposited on Si (100) substrates by chemical vapour deposition (CVD) at atmospheric pressure (1 atm). The only solid source used here is zinc acetate, (CH3COO)2Zn, and the carrier gas is nitrogen. The sample, which was prepared at 550 degrees C during growth and then annealed in air at 900 degrees C, has only a ZnO (002) diffraction peak at 34.6 degrees with its FWHM of 0.23 degrees in the XRD pattern. The room-temperature PL spectrum shows a strong ultraviolet emission with the peak centred at 380 nm. We analysed the effects of many factors, such as the source, substrates, growth and annealing temperatures, and annealing ambience, on the structural and optical properties of our prepared ZnO films.

Effect of Al Doping on Properties of SiC Films

Undoped and Al-doped 3C-SiC films are deposited on Si(100) substrates by low-pressure chemical vapour deposition. Effects of aluminium incorporation on crystallinity, strain stress, surface morphology and growth rate of SiC films have been investigated. The x-ray diffraction patterns and rocking curves indicate that the crystallinity is improved with aluminium doping. Raman scatting patterns also demonstrate that the strain stress in SiC films is released due to the incorporation of Al ions and the increase of film thickness. Furthermore, due to the catalysis of surface reaction which is induced by trimethylaluminium, the growth rate is increased greatly and the growth process varies from three-dimensional island-growth mode to step-flow growth mode.

Effect of High Temperature Annealing on Conduction-Type ZnO Films Prepared by Direct-Current Magnetron Sputtering

We experimentally find that the ZnO thin films deposited by dc-magnetron sputtering have different conduction types after annealing at high temperature in different ambient. Hall measurements show that ZnO films annealed at 1100?C in N2 and in O2 ambient become n-type and p-type, respectively. This is due to the generation of different intrinsic defects by annealing in different ambient. X-ray photoelectron spectroscopy and photolumi-nescence measurements indicate that zinc interstitial becomes a main defects after annealing at 1100?C in N2 ambient, and these defects play an important role for n-type conductivity of ZnO. While the ZnO films annealed at 1100?C in O2 ambient, the oxygen antisite contributes ZnO films to p-type.