RF预处理对ZnO/Si生长的影响

Effect on Radio Freqency Plasma Pretreatment on ZnO/Si Thin Films

氧化锌是一种Ⅱ-Ⅵ族直接带隙的宽禁带半导体材料，其室温下的禁带宽度3．36eV，由于其具有紫外发光的特性，近来受到研究者的广泛关注。由于ZnO在高效率光散发设备和其它光学方面有应用前景，所以要进行高质量的ZnO薄膜制备的研究。由于晶格失配，ZnO／Si的异质结质量不高，现在主要应用过渡层或表面处理的方法进行改善。本文用MOCVD设备生长ZnO／Si薄膜，所用载气为N2，反应源为CO2和DEZ，衬底为Si（111）单晶外延片。除了对衬底进行常规的化学清洗以外，在生长前进行Ar RF的预处理，是氩离子对硅表面进行一定的破坏，处理能量从0-110W进行了梯度变化，再以同样的生长条件进行原位生长。对于样品我们分别作了XRD、PL、AFM测量，发现Ar RF预处理对薄膜结晶有很大影响，未作处理的样品一般呈多晶态，而处理后的样品在一定能量范围内晶格取向有显著提高，但随预处理能量达到一定限值后取向性被破坏，XRD测试图如1、2、3。预处理对于发光也有很大的影响，在一定能量范围内发光强度只随处理能量加大缓慢衰减，但在高能量状态下，发光明显减弱，峰位也随之变化。可见氩离子轰击硅表面形成了缺陷，这些缺陷在生长中顺延在ZnO部分，并且这些缺陷是发光淬灭中心，随能量的增加而增加。PL测试图如4。通过AFM分析样品的粗糙度，发现预处理对表面粗糙度有减低的作用，随着处理能量的增加，表面粗糙度下降。

ZnO is a Ⅱ-Ⅵ compound semiconductor material with a wide direct band gap of 3.36eV at room temperature. Recently,it has attracted great attention due to its ultraviolet luminescence. For the use of ZnO in high-efficiency light emitting devices and other optical applications ,high quality single crystal ZnO films are required. But it is difficult to get high quality ZnO films on the Si substrates because of the large lattice mismatch. Using the buffer layer or substrate pretreatment is a way to get high quality ZnO films. ZnO films have been deposited on Si （ 111 ） substrates by low-pressure MOCVD. Diethyl-Zinc （ Zn （ C2H5 ） 2 ） and carbon dioxide （ CO2 ） were used. Si （ 111 ） substrates were pretreated by RF plasma before growth. The power of RF plasma was arranged from OW to 110W. Then ZnO thin films were grown in situ. The great effect of RF plasma pretreatment on the structure and luminescence properties was investigated by X-ray diffraction （ XRD ）, atomic force microscope （ AFM ） and photoluminescence （PL） spectrum at room temperature. The quality and surface roughness of ZnO thin films using pretreatument are better. The orientation of ZnO films was degraded when the pretreatment energy achieved the certain limiting value. The UV emission intensity decreased because the argon ion bombardment silicon surface has formed the crystal defect which makes quenching of luminescence in growth