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Electrical Properties of ZnS / silicon nanoporous pillar array heterostructure

Author: JiaHeShun
Tutor: LiXinJian
School: Zhengzhou University
Course: Condensed Matter Physics
Keywords: ZnS/Si nanoporous pillar array heterojunction composite system electric transport mechanism space-charge-limited current field emission
CLC: TB383.1
Type: Master's thesis
Year: 2009
Downloads: 22
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Abstract

Since 1980s, the emergence and development of nanotechnology have dramatically changed the ways of human life and thinking. Especially, the request, which is on the question of energy production technology to a smaller, more sophisticated, higher-level development, is made the scientific research and production technology of nano-composite materials to be hot nowadays. Among them, the researches of integrated devices and their common lattice mismatch problem have been a very important topic. The surface physical properties study of heterojunction will be a very important aspect.In this paper, liquid phase chemical reactions were used to prepare ZnS/Si-NPA heterojunction devices. The reaction on the morphology of heterojunction devices, electric transport, and field emission properties was discussed. The electric transport mechanism of ZnS and Si-NPA heterojunction surface and field emission mechanism on ZnS surface have also been studied. The main points in this paper are as follows:1. The preparation and representation of ZnS/Si-NPABy scanning electron microscopy (SEM), X-ray diffraction (XRD) to determine the morphology of the samples as well as the composition, it can be seen: (a)A layer of dense continuous ZnS nano-crystal film was deposited at the surface of Si-NPA through the liquid phase reaction, and then the composition of the selective growth of ZnS/Si-NPA heterojunction system was generated; (b)With the concentration of reaction solution to increase, nano-ZnS formation also increased; (c)The growth of nano-ZnS with the select-position on the Silicon Pillars increased with the increase of surface porosity; (d)Suitable annealing temperature was conducive to generate a better crystallization of ZnS nanoparticles on the substrate. By changing the reagents and methods, the same types of selective growth of ZnS/Si-NPA heterojunction composite system were also formed.2. Heterojunction electric transport mechanism Because the good ohmic contacts between ITO/ZnS, Si-NPA/Si, Si/Ag were shown, the electric transport mechanism of heterojunction between ZnS and Si-NPA can be well studied by testing the current-voltage characteristics. Heterojunction semiconductor device performanced characteristics of the rectifier; fitting ideal diode factors which are greater than one, such a departure was mainly caused by two reasons: the existence of ohmic contacts between the metal and semiconductor; the lattice mismatch between ZnS and Si-NPA.The impact study of different concentration and temperature on heterojunction device was showed that the heterojunction electric transport mechanism between ZnS and Si-NPA can be analyzed using space-charge-limited current model, and the characteristic temperature of trap distribution Tc was 1384K.3. Analysis of field emission propertiesThe field emission properties of different concentrations were tested. The turn-on field strength was lower with the increase of sediment concentration, and all of them had a small turn-on field. The reasons included: (a) The electron transmission capacity on a separate taper silicon surface was less than that of surface microstructure commixing ZnS and Si-NPA after the deposition of ZnS, and with the increase in the thickness of ZnS deposition on the sample surface the electron transport capacity was enhanced; (b) The work function of ZnS is less than Si; (c) On samples surface with the rules of the fairly uniform and mutual separation heterojunction structure array, you can eliminate part of the shielding effect of the negative impact, which is also conducive to have a small turn-on field.Two consecutive analysis of field emission factor was discussed. This deviation with the theoretical formula had two causes: (a) the effects of equivalent resistance of electron injection and transport; (b) the impact of physical morphology with the presence of high voltage intensity in the emission process. In the experimental process, the sample was exhibited spark if electric field strength overhead, meanwhile the top of the pillars might be spalling, and some were melt to be a flat silicon melt reactor at the bottom of the porous silicon. The spark eventually led to the electron breakdown and short circuit; even more, in the process of spark ZnS oxidation phenomenon would appear.

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