ZnO薄膜的掺杂特性

Characteristics of Nitrogen Doped ZnO Film

通过MOCVD方法生长的ZnO薄膜一般为富锌生长,呈n型电导,要想得到高阻或低阻p-ZnO薄膜需要对其进行掺杂施主或受主杂质。主要研究在生长过程中通过NH_3对ZnO薄膜进行氮掺杂的情况,利用优化生长条件,即生长温度为610℃,Ar气(携带DEZn)流量为4 sccm,O_2流量为120 sccm,N_2流量为600 sccm,得到在NH_3流量为80 sccm时生长样品的结晶质量最高,在掺杂薄膜中NH_3流量高于或低于80 sccm时,样品的表面形貌都将变差,只有在80 sccm时表面粗糙度最低晶粒最小,表明该流量下获得的样品表面较光滑致密。所以80 sccmNH_3流量为在R面蓝宝石上生长<110>取向ZnO薄膜的最佳掺杂流量。Hall测量结果表明,NH_3流量为50 sccm的样品电导呈弱p型,电阻率为102Ω·cm,空穴载流子浓度为+1.69×10^(16)cm^(-3),迁移率为3.6cm^2·V^(-1)·s^(-1);当NH_3流量增加时样品的电导呈n型,电阻率最高达10~8Ω·cm,我们认为与进入ZnO薄膜的H的量有关,并对其变化机理进行了详细的分析。

ZnO is a direct wide-band gap semiconductor with WZ crystal structure. Due to the low growth tempera- ture and high exciton binding energy (60 meV) at room temperature, it is an ideal semiconductor material with blue light enission. As the development of semiconductor growth technology, high quality ZnO can be obtained, and the research in ZnO attracts much more attention again. In this paper, high quality ZnO thin films on sapphire substrate have been obtained by MOCVD system designed by ourselves. At the same time, the properties of annealed and doped ZnO films have been investigated in details, and good results have been achieved. According to the principle of MOCVD and in order to solve the problem in ZnO growth process, new-type plasma enhanced MOCVD system has been designed and fabricated. The precursors (DEZn and O_2) has been introduced into the reactor by two gas lines, respectively. And the precursors arrive to the surface of sapphire sub- strate by two separated special injectors. The substrate holder can be rotated at high speed and is uniformly heated by a special resistive heater. In order to balance the thermal flow, N_2 is introduced into the reactor uniformly from the upside of the reactor. All above design can reduced the pre-reaction of DEZn and O_2 during the ZnO growth and uniform ZnO films may be grown by this MOCVD system. Furthermore, the plasma generator has been added to the MOCVD system in order to improve doping efficiency during ZnO growth process and to obtain high resistivity or p-type ZnO films. High quality ZnO films have been firsly grown on sapphire substrate in optimized growth condition by MOCVD. At the same time, the doping properties of NH_3 in ZnO film grown on R-plane sapphire were also firstly investigated. After optimized the growth conditions, only〈110〉oriented ZnO film were obtained under NH_3 flux of 80 sccm. Furthermore, the FWHM of ZnO (110) XRD peak is only 0.50°. The AFM images sbow that the surface of the film is the most smooth. Up or low the flux, the surface will become rough and the crystal quality also de- creases. The Hall measurements show that the sample grown under NH_3 flux Of 50 sccm is low p-type conductor with the resisitivity 102Ω·cm, hole concentration + 1.69×10^(16)cm^(-3) and mobility 3.6cm^2·V^(-1)·s^(-1). The XPS spec- tra show that nitrogen and zinc atom forms N—Zn bond under NH_3 flux of 50 sccm. As the flux increase, some hy- drogen atom is introduced into ZnO film, and the conductivity change into n-type. The sample resistivity is up to 10~8Ω·cm under NH_3 flux of 80 sccm.