【作者】 刘胜芳；

【导师】 秦福文；

【作者基本信息】 大连理工大学 ， 凝聚态物理学， 2010， 硕士

【摘要】 氮化镓(GaN)作为一种宽直接带隙(室温禁带宽度为3.39eV)半导体材料,具有电子饱和漂移速度高、热导系数高、介电常数小、化学性质稳定和热稳定性好等特性。GaN基器件已经广泛应用于半导体发光二极管(LED)、半导体激光器(LD)等光电子器件上,同时由于它还具有高的声波速率、很好的压电特性,又使其成为制备兆赫兹级声表面波器件(SAW)的理想压电材料。目前GaN薄膜主要是在蓝宝石(α-Al2O3)碳化硅(SiC)、氧化锌(ZnO)和硅片等异质衬底上制备的,其中最常用的是α-Al2O3衬底,但α-Al2O3衬底存在许多缺点如：价格昂贵、难以实现大面积沉积、不导电、热导率低等,使用α-Al2O3做衬底限制了GaN在器件中的进一步应用。金属是电和热的良导体,用金属做衬底,一方面可以改善器件的电学特性、解决散热等问题,另一方面还可以直接用作下电极,因此有研究组将α-Al2O3衬底上生长的GaN薄膜剥离下来转移到金属上,但工艺要求高,成品率低。干法刻蚀在器件下电极的制备中广泛使用,但是由此产生的刻蚀损伤对器件性能影响也较大。如果能在金属上直接沉积出高质量的GaN薄膜,则不需要复杂的工艺程序,就可以改善器件的电学特性、解决散热问题和满足器件对金属下电极的使用需求。目前有以Cu、Ag等金属为衬底沉积c轴择优取向GaN薄膜的报导,但是这些研究中生长温度都较高。铝也是电和热的良导体并且还是一种广泛使用的金属电极,但熔点较低(660.37℃),且铝膜的熔点更低,过高的生长温度会使铝膜熔化,所以要在铝膜上沉积GaN薄膜要求沉积温度不能过高。本文采用镀铝膜玻璃为衬底,低温沉积了结晶质量较好的GaN薄膜(沉积温度只有430℃)。相对于一些研究中使用单晶金属为衬底,本实验采用廉价的镀铝玻璃为衬底,可进一步节约成本且能够实现大面积沉积。本文首先使用射频磁控溅射方法在康宁7101型普通玻璃表面镀一层厚约300nm的(111)择优取向的多晶铝薄膜,然后采用电子回旋共振-等离子体增强金属有机物化学气相沉积(ECR-PEMOCVD)方法,以镀铝玻璃为衬底,三甲基镓(TMGa)为镓源(以氢气为载气),高纯氮气(纯度为5N)为氮源,低温沉积了高度c轴择优取向GaN薄膜。利用反射高能电子衍射(RHEED)、X射线衍射(XRD)、扫描电镜(SEM)和拉曼光谱(Raman)研究了衬底氮化时间、TMGa流量、衬底温度对制备GaN薄膜质量的影响。得出了在镀铝膜玻璃衬底上沉积GaN薄膜的适宜工艺参数,实验结果表明,在其他沉积参数固定不变的条件下,以表面较为平整的镀铝膜玻璃为衬底,衬底氮化60min, TMGa流量为2.0sccm,沉积温度为430℃和470℃的条件下,制备的GaN薄膜结晶质量较好。更多还原

【Abstract】 GaN is a direct wide-band gap semiconductor with a band-gap of 3.39 eV at room temperature, and possesses some superior characteristics including high electron saturation drift velocity, high thermal conductivity, low dielectric constant, good chemical property and good thermal stability and so on. GaN-based semiconductor devices have been widely used for the fabrication of various photonic devices such as blue-green lighting emission diode (LED) and laser diode (LD). In addition, GaN has also been considered as an ideal material to produce megahertz (MHz) level SAW for its advantage of high sound wave velocity as well as good piezoelectricity characteristic. Nowadays, GaN thin film is mainly deposited on foreign substrates such as a-Al2O3、SiC、ZnO and Si, and a-Al2O3 is the most commonly used one among all these substrate. However, the intrinsic drawback of a-Al2O3, including expensive price, the difficulty in realizing large area deposition, poor electric conduction, low heat conductivity and so on, has obviously restricted its further application in GaN device. Compared witha-Al2O3, metal substrate exhibits some merits such as good electricity and thermal properties and thus can improve the device electrical characteristic and solve the radiation if the GaN film is deposited on it. On the other hand, it also can serve as underneath electrode directly. Therefore, the growth of GaN thin film has been shifted from sapphire substrate to metal substrate. However, it requires high technology and the final rate of finished product is quite low. Dry etching technology has been widely used to produce the underneath electrode, but it may bring some damage to device and thus influences the device performance. If the high quality GaN thin film can be deposited on metal substrate directly, it may improve the device electricity characteristic, solving the radiation and meeting the requirement of devices’ underneath electrode.Nowadays, it has been reported that c-axis oriented GaN films can be deposited directly on metal substrates such as Cu, Ag, but the deposition temperature is a little high. Al metal has been also used as metal electrode for its good electricity and thermal properties. However, it may melt under the high deposited temperature. So it is necessary to deposit good GaN films on Al substrate at lower temperature. In this work, the GaN films with good crystallization quality has been obtained on Al films, which was coated on glass substrate beforehand, using the low temperature depositing technology, and the actual deposited temperature used in the growth of GaN film is 430℃. Therefore, it can be seen that the method proposed in this work provides an effective way to produce GaN films on Al coated glass substrate with lower cost and large area growth, comparing with other traditional methods.In this work, (111)-oriented polytropism Al film with a thickness of 300 nm was first coated on glass substrate by the RF magnetron sputtering, and then c-axis oriented GaN film with good crystal quality was deposited on the as-coated Al film on glass substrate, using the electron cyclotron resonance plasma enhanced metal organic chemical vapor deposition (ECR-PEMOCVD) at low temperature. During the deposition, Trimethyl-gallium (TMGa) and high purity N2 were employed as Ga and N sources, respectively, and high purity H2 was used as carrier gas. Finally, the effect of substrate nitriding time, Trimethyl-gallium (TMGa) flow rate, deposition temperature on the GaN film quality was systemically studied using in-situ reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD), scanning electron microscope (SEM), Raman spectrum (Raman), and the optimizing deposition parameters for GaN films deposition on Al-coated glass substrates can be confirmed. The results show that the crystalline characteristics of prepared GaN films is better if Al-coated glass substrate is smooth, the Al films are nitrided one hour,the TMGa flow rate is 2.0sccm and the deposition tempurature is 430℃or 470℃, all other parameters are left unchange.更多还原