| 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.
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