【作者】 李杨超；

【导师】 严辉；

【作者基本信息】 北京工业大学 ， 材料科学与工程， 2010， 硕士

【摘要】 透明氧化物半导体(TOS)是一种在可见光区域具有良好的透光性,并且导电性优异的光电材料,由于具备这两个特性,被广泛应用于电子工业领域。根据导电特性的不同分为n型与p型两类。目前n型TOS已经被广泛应用,而p型TOS相对缺乏。本文根据价带化学修饰理论,以p型铜铁矿结构的CuCrO2薄膜为研究对象,采用磁控溅射技术制备CuCrO2薄膜,摸索出薄膜制备工艺,通过二价离子受主掺杂改善薄膜的导电性,研究了厚度对CuCrO2:Mg(9mol%)薄膜透明导电性的影响,制备出p-CuCrO2:Mg(9mol%)/n-Si p-n结,具体归纳起来可以概括为以下几个部分。1.本文摸索CuCrO2薄膜的最佳制备工艺。通过对衬底温度的调制,500℃时获得最高室温电导率为27.1 S·cm-1的薄膜,在可见光区的透过率为15%-20%。由于750℃以内沉积的CuCrO2薄膜可见光透过率很低,通过调节异位退火温度成功制备了透过率与导电性良好的CuCrO2薄膜。薄膜透过率随退火温度升高而增大,电导率则随退火温度升高而降低。900℃时,综合性能最好,平均可见光达到50-60%;电导率为1.7×10-2 S·cm-1。变化溅射功率,随着溅射功率的增加,薄膜可见光透过率降低,电导率提高。100W溅射的薄膜综合透明导电性能最优,室温电导率为0.075 S·cm-1,可见光透过率为50%-60%。改变氧分压来调节薄膜中的氧浓度,在氧分压下沉积的薄膜电导率显著降低,透过率为10%-15%,900℃退火后,薄膜的透过率提高到60%-70%,但是薄膜不导电,没有氧分压的薄膜,室温电导率降低到1.5×10-3 S·cm-1。最佳溅射参数定为衬底温度为500℃,溅射功率为100W,氧分压为0%,溅射完成进行900℃异位退火。2.在CuCrO2薄膜制备工艺优化基础上,制备出结晶性较好的CuCrO2:Zn,CuCrO2:Mg薄膜,薄膜的平均可见光透过率在30%-50%之间。所有薄膜在200K以上均符合半导体热激活导电机制,对于所有掺杂系列的薄膜而言,当Mg掺杂量为0.09时,薄膜具有最好的导电性,室温电导率为0.062 S·cm-1,比CuCrO2的样品提高了400倍,且Hall测试表明,该样品为p型半导体。3.研究厚度对CuCrO2:Mg(9mol%)薄膜性能影响,随着厚度增加,薄膜晶粒尺寸增大,压应力减小,使得空穴载流子浓度与迁移率增加,电导率提高,但薄膜的可见光透过率降低。当厚度为310nm时,薄膜具有较好的综合透明导电性。4.从器件角度考虑,本文制备出p-CuCrO2:Mg(9mol%)/n-Si p-n结,室温下样品呈现出明显的整流特性,开启电压为1V。粗略计算电压为5V的正向电流与反向电流的比值,正反电流比值约为8.2。根据p-n+单边突变结理论进行了拟合,发现界面态效应和串联电阻效应是影响该异质结整流特性的重要因素。更多还原

【Abstract】 Transparent Semiconductor Oxides(TOS) have the feature of optical transparency in the visible region and controllable electrical conductivity, and they are widely used as transparent electrode for solar cells, liquid crystal display, light emitting diodes in electronic industry. However, the application of TOS has been restricted to n-type semiconductor, the lack of p-type TOS has limited their applications. Based on the theory called the chemical modulation of the valence band(CMVB), we selected delafossite structure CuCrO2 as the subject to investigate. We prepared the CuCrO2 films by radio frequency magnetron sputtering technique. The main results we achieved are as following:1. The optimized parameters have been obtained successfully to deposited CuCrO2 films. The substrate temperature has been investigated. The maximum conductivity of CuCrO2 film is 27.1 S·cm-1 when the substrate temperature reaches at 500℃. The transmittance of CuCrO2 film is about 10%-15% in the visible light range. Since the transparency of deposited CuCrO2 films is very low, CuCrO2 films were annealed under high pure nitrogen atomosphere. The average transmittance increases with the increase of annealing temperature, but the conductivity decreased with the increasing of annealing temperature. The optimum properties for CuCrO2 films are obtained by annealing at 900℃. Moreover, the sputtering power influences the properties of CuCrO2 films. It is founded that the optical transmittance of the films decreases, but the conductivity of the films enhances when the sputtering power increases. The CuCrO2 films have optimum properties of transparent conductivity at 100W. Furthermore, by adjusting oxygen partial pressure on the properties of the films were studied. The conductivity of the films decreases notably when sputtering at oxygen partial pressure. The transmittance is 10%-15% in the visible range. After annealing at 900℃,the transmittance of the films increases to 60%-70% for the films deposited at oxygen partial pressure, but the films are not conductive. The conductivity of the films at 0% oxygen partial pressure is 1.5×10-3 Scm-1. Considering the optimum sputtering parameter, the substrates temperature is 500℃, the sputtering power is 100W, the partial oxygen pressure is 0%, and the annealing temperature is about 900℃.2. Zn, Mg doped CuCrO2 with delafossite structure were successfully prepared by radio frequency magnetron sputtering technique. The transmittance is about 30%-50% in the visible light range. The temperature dependence of conductivity can be described by the thermal activation theory when the temperature is above 200K. At the room temperature, the maximum electrical conductivity for all doped CuCrO2 film is 0.062 S·cm-1 for 9mol% Mg doped CuCrO2 which is 400 times higher than that of undoped sample. Hall effects measurements prove that the sample is p-type semiconductor.3. The thickness effect on the structure, optical and electrical properties of the 9mol% Mg doped CuCrO2 thin films were investigated. The grain size increases as the film thickness grows, while the compressive strain increases as the film thickness decreases. The average transmittance of the films decreases as film thickness grows in the visible range. The electrical conductivity decreases monotonously as the film thickness decreases mainly because of hole concentration and mobility declining. The hole concentration decreases when the lattice compressive strain enhances. The carrier mobility declining as the grain size becomes larger because of the stronger grain boundary scattering effect.4. As for the device applications, p-CuCrO2:Mg(9mol%)/n-Si p-n junction has been prepared on low resistance Si substrate. Based on the linear I-V characterization of Ni-Si-Ni, Ni-CuCrO2:Mg(9mol%)-Ni, the I-V characterization shows that the junction has the rectifying property with the cut-in voltage of 1V. The ratio of the forward current to the reverse current reached 8.2 at the bias voltage of 5V. Using the theory of p-n+ one-sided step junction to simulate I-V curves, it is found that the effects of the interfacial states and junction resistance should not be neglected to analyze the rectifying property of the heterojunctions.更多还原