Study On Field Effect Properties Of CdS Nanoribbons Doped With Phosphorus And Indium

CdS is one of the most importantⅡ-Ⅵgroup materials with a band-gap of 2.42eV at room temperature, which has attracted much more interests because of its special characteristics and potential applications. Study of CdS nanoribbons focus on its synthesis and structure, especially the properties of the light emission diodes (LED), sensors and field-effect-transistors (FET). The doping, one of methods to improve the properties of materials, is useful for investigating characteristics and applications of CdS nanoribbons. Recently, doping-effect of some dopants, such as Co,Mn,Fe,Hg and Cl and so on, has been reported. However, few researches have been reported on phosphorus doped CdS so far. Although indium doped CdS has been investigated, the electric transports of CdS nanoribbons are still worth of studying further.In this dissertation, indium-doped and different doping levels phosphorus-doped CdS nanoribbons have been synthesized by thermally evaporating using indium grain and red phosphorus powder as dopant sources. The alteration of lattice constants caused by dopant has also been studied. Moreover, the properties of FETs based on the as-prepared CdS nanoribbons have been studied too. The results are following:1. Indium or phosphorus doped CdS nanoribbons have been synthesized by co-thermal evaporation. The size of as-synthesized CdS nanoribbons can be realized by analysis of morphology. For the indium doped CdS nanoribbons, they have length of 50~90μm and width of 1.5~3.5μm with thickness of 20~50nm. For the heavily phosphorus doped CdS nanoribbons, they have length of 180~400μm and width of 4~6μm with thickness of 80~110nm. For the lightly phosphorus doped CdS nanoribbons, they have length of 60~140μm and width of 2~4μm with thickness of 30~60nm.2. Analysis of component and structure shows that the indium and phosphorus substitute the Cd and S in the crystal structure, respectively. The distance of closed crystal planes increase, which can be ascribed that radius of the dopant is larger than that of substituted elements. When the indium is doped into the CdS, the a lattice parameter increases from 4.129 ? to 4.317 ? and the c lattice parameter increases from 6.707 ? to 7.146 ?. When the doping level of phosphorus alter from lightly to heavily, the a lattice parameter increases from 4.126 ? to 0.4.132 ? and the c lattice parameter increases from 6.692 ? to 6.717 ?.3. For the nanodevices based on single as-doped CdS nanoribbon, the contact between the nanoribbon and the electrodes is ohmic. The concentration of carriers and conductance of as-doped CdS nanoribbon increase obviously, some nanoribbons have three orders of magnitude increases. Analysis of the Vg-dependent Ids versus Vds curves reveals that the conductance increases with the increase of Vg, therefore the nanoribbons doped by indium and phosphorus are n-type semiconductors, which can be attributed to the a mass of electrons by self-compensation effects. The hydrogen, part of the carrier gas, may enhance this effect.4. The conductance of single indium or phosphorus doped CdS nanoribbons is high, and the on/off ratio is low relatively. However, they still have high electronic mobility respectively. For the heavily phosphorus doped CdS nanoribbons, the electronic mobility is about 175cm2/Vs. For the indium doped CdS namoribbons, the electronic mobility is about 325cm2/Vs, which is close to that of bulk CdS single-crystal (340cm2/Vs).In conclusion, the indium and phosphorus doped effects to crystal structures and properties of the CdS nanoribbons electric transports have been discussed in this dissertation, which could provide references for studying the field-effect properties and applications of CdS nanoribbons.