范德堡方法在ZnO薄膜测试中的应用

Van der Pauw Method in the Test of ZnO Film

近年来 ,随着对宽禁带半导体材料 ,氧化锌薄膜研究的快速发展 ,对其电学性质的研究也显得尤为重要。主要介绍范德堡方法在ZnO薄膜电学性质测量中的应用 。

ZnO is a wide band gap semiconductor with 3 36 eV at room temperature. It has been studied for decades for its many applications, such as surface acoustic waveguide, transparent electrodes for some solar cells and buffer layer for epitaxy of GaN. In recent years, ZnO film attracted more attention due to its applications in photoelectric materials. It has been found to be possibly used in ultraviolet laser devices due to its ability to emit stimu lated ultraviolet photons. The shorter wavelength laser devices can provide many new applications. In order to fabricate photo electronic diodes, research on the electrical properties is now urgently needed. Using the method of Hall effect experiment, we can get some information on the semiconductor, such as the carrier concentration, conductance and transfer rate. For the sample of films, Van der Pauw method is very useful. It can be applied to measure the samples with anomaly geometry. But there were few detailed reports on the measu ring of ZnO films by using this method. Using Van der Pauw method to measure the ZnO films, the first problem is to prepare electrode, which is ohmic contact with ZnO films. Al is mostly used as ohmic electrode, but we found another Ag alloy material with lower contact resistance, which is better as ohmic electrode than Al. Second, it is stable at low temperature(77 K),but Al is not. The last, the Ag alloy electrode is much easier to prepare. Using the Ag alloy as the ohmic contact, we get the carrier concentration of the sputtered ZnO prepared on glass substrate at room temperature to be 1 04×10 17 cm -3 ; the resistivity of 2 25 Ω·cm and the transfer rate of 26 7 cm 2/V·s. We also get the temperature dependence of DC resistivity of the sputtered ZnO films. At high temperature (>280 K), σ formally obeys the following formula: σ = σ 0exp(- E a/ KT ) where σ 0 is a pre exponential factor, E a the activation energy for band conduction, and K the Boltzmanm constant. And we find the activation energy of sputtered ZnO is 0 035 eV. At lower temperature(77～280 K),the dependence is different from the normal semiconductor. It may be caused by the drift of the impurity ions in grain boundary barrier.