【作者】 张景林；

【导师】 杜国同；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2004， 硕士

【摘要】 ZnO是一种具有纤锌矿晶体结构的直接宽带隙半导体材料，禁带宽度为3.37eV，室温下激子束缚能高达60meV，高于ZnSe和GaN。是一种理想的蓝光半导体材料，因此其研究被称为“低温蓝光工程”，在诸如气敏传感受器、光电探测器、声表面波器件、电致发光器件、发光二极管、太阳能电池等光电器件方面具有较大的应用潜力。生长ZnO薄膜的方法很多，可采用诸如：磁控溅射、分子束外延、脉冲激光沉积、金属有机化合物气相沉积、喷雾热解等方法。本文采用我们自己组装设计的具有自主知识产权的MOCVD系统，生长出了高质量的ZnO薄膜。我们所做的工作如下：1、以DEZn和O2为源，利用MOCVD系统在C-Al2O3衬底上生长出了高质量的ZnO薄膜，衬底温度580℃、反应室压力480pa、Ar(作为携带DEZn的载气)流速为1.25×10-4mol/min、氧气流速为6.0×10-3mol/min。由原子力显微镜图可见薄膜表面平整，颗粒均匀细密，测得薄膜的电阻率为0.209Ω·cm，迁移率为8cm2/V·S，载流子浓度为-3.73×108cm-3，表面生长的薄膜为低阻n型导电；XRD分析表明：ZnO (0002) 面衍射峰峰位在2θ=34.48°处，其半高宽FWHM为0.184°，根据布拉格方程，可计算薄膜中平均晶粒尺寸D=47.12nm；室温Raman谱中，只观测到了E2(high)模式和A1(LO)振动模式，说明ZnO薄膜形成良好的纤锌矿结构；在室PL谱中出现ZnO薄膜的强的带边发射峰和弱的深能级发射峰，带边发射峰位于3.28eV，两处峰的强度比值为40:1，说明生长的ZnO薄膜具有较高的光学质量。2、此外，我们在衬底温度为610℃、反应室压力为180pa、DEZn流速为6.25×10-5mol/min，氧气流量依次为3×10-3mol/min、8×10-3mol/min、2×10-2mol/min的情形下进行了ZnO薄膜的生长研究。XRD谱表明，具有六方晶系纤锌矿结构的ZnO薄膜的(0002) 衍射峰被观察到，分别位于2θ<WP=59>=34.56°，34.50°，和34.48°。对于C样品，生长的ZnO薄膜除(0002)面衍射峰外，还有位于2θ=47.52°的（）面衍射峰出现，并且随着生长过程中氧气流量的增加，(0002)面衍射峰峰强逐渐减弱，（0002）峰的半高宽依次为0.20°、0.26°和0.30°。在当前生长条件下，随氧气流量的增加，ZnO薄膜结晶质量在下降，由单一c轴取向薄膜已转成多晶薄膜。随O2气流量的增加，生成的ZnO薄膜表面的平均晶粒尺寸变小，柱状晶粒尺寸更加均匀，粗糙度变小，表面更加光滑平整，对于A、B、C三种样品，其均方根粗糙度数值分别为47.16nm，23.59nm，9.04nm。ZnO薄膜在He-Cd激光器激发下室温PL谱显示，随着氧气流量的增加，深能级发光峰明显减弱。这表明，ZnO薄膜的光致发光特性更重要的不是依赖于薄膜的微观结构质量，而是依赖于薄膜中的Zn、O组份配比。3、最后，我们在衬底温度为600℃、反应室压力为210pa、氧气流量180sccm、氩气（携带DEZn）流量2sccm的条件，通过改变冷阱的温度、从而改变实际反应时Zn源的浓度，进行ZnO薄膜的富锌生长研究。通常人们认为光荧光谱中观察到的深能级复合发光来源包括：导带和离子化的Zn空位（VZnx）之间的复合、施主（Zni）与受主（VZnx）之间的复合、导带和氧空位（Vo）之间的复合、ZnO晶体中的填隙Zn离子（Zni）和价带的复合以及导带和O错位（OZn）之间的复合。从薄膜的室温PL谱中可以看出，深能级跃迁发光峰的强度是依次减弱的。从而也可知，在此种条件下生长的ZnO薄膜，其深能级跃迁发光峰的强度与薄膜中VO和Zni关系不大，即导带和氧空位（Vo）之间的复合、填隙锌（Zni）和价带的复合对深能级发光峰强度的贡献不是很大。另外由于氧原子半径大于锌原子半径，因此形成填隙氧（Oi）的可能性较小，所以Oi缺陷与深能级跃迁发光关系也不大，我们可以认为与样品深能级跃迁发光关系较为密切地是VZn×和OZn缺陷。更多还原

【Abstract】 ZnO is a direct wide-band gap semiconductor with wurtzite crystal structural. Its wide band gap is 3.37eV at room temperature and exciton binding energy is as large as 60meV, which is much higher than that of ZnSe and GaN. It is an ideal semiconductor material in blue light range and the research in ZnO is named as “low temperature blue project ”. Furthermore , it has more potential applications in optoelectronic devides such as gas sensor, photodetectors, surface acoustic wave devices, electroluminescence devices , light emitting diodes and solar cells. ZnO films have been grown by many methods, such as magnetron sputtering, molecular beam epitaxy (MBE), pulsed laser deposition (PLD), spray pyrolysis and metal organic chemical vapor deposition (MOCVD). In this paper, High quality ZnO films were obtained from the c-Al2O3 substrates by MOCVD, which has the right of independence knowledge of ourself. Our works are as follows:(1) High-quality ZnO films were deposited on c-Al2O3 substrates by MOCVD using Diethylzinc (DEZn) and oxygen. The flow rate of high-purity Ar gas (99.999%) , which was applied as the carried gas of DEZn, was 1.25×10-4mol/min and that of O2 gas was 6.0×10-3mol/min.The working pressure of the chamber was kept at 480Pa. Then, ZnO thin films were deposited at the temperature of 580℃.The AFM 3D surface images showed that the surface of ZnO thin films was relatively flat and dense. The resistivity of ZnO thin films was 0.209Ω·cm, and the mobility is 8cm2/V·S, the carrier concentration was –3.73×10-8/cm3. Those indicated that the ZnO thin films was low resistivity and n-type.The XRD spectra of ZnO thin films showed that the (0002) peak was at 2θ=34.48°and the full width at half maximum (FWHM) was 0.184°, According to the Bragg equation, we could obtain the mean grain size (D) was 47.12nm. Raman scattering was performed at room temperature showed that only the A1(LO) and E2(high) modes were observed, which indicated the ZnO thin films had the wurtzite structure. It was found there was a strong ultraviolet near-band-edge emission(NBE) and a week deep level emission(DLE) in the PL spectra at room temperature. The <WP=61>NBE peak was located at 3.28eV, and the intensity ratio of the NBE to DLE was 40:1, which suggested that the ZnO thin film had a high optical quality.(2) Another, the flow rate of DEZn was 6.25×10-5mol/min, the total pressure of the reactor was kept a constant of 180Pa, All the ZnO thin films were at substrate temperature of 610℃ at different flow rate of oxygen, which were 3×10-3mol/min, 8×10-3mol/min and 2×10-2mol/min. Under those conditions, we obtained sample A，B，and C. From the XRD spectrum of the ZnO thin films, the (0002) peaks for sample a, b, and c were at 2θ=34.56°,34.50°, and 34.48°, respectively. But a weak peak at 2θ=47.52°was detected for sample c, which was (102) diffraction peak of ZnO films. With the increase of the flow rate of oxygen, the intensity of (002) diffraction peak decreased for three samples, and the FWHM broadened from 0.20°, 0.26° to 0.30°.This indicated that the crystalline quality degraded from single-oriented crystal to polycrystalline with the increase of the oxygen content. From the AFM 3D images of ZnO films, We could see that the films were deposited in a column-by-column growth process and the mean grain size became smaller when the flow rate of oxygen increased, and the root-mean-square roughness decreased which was 47.16nm, 23.59nm, and 9.04nm for sample a, b and c, respectively. From the PL spectra of ZnO films, with increasing the flow rate of oxygen, the DLE was weakened. It indicated that the DLE might originate from the oxygen vacancies (Vo), whose concentration decreased under oxygen-enriched condition. It could be concluded that the UV emission was more dependent on the stoichiometry than the microstructural quality of the films. (3) Finally, the ZnO films were obtained under those conditions: the flow rate of O2 was kept at 180sccm, the pressure of the reactor was kept at 210Pa, The flow rat更多还原