The Characteristics Of GaN Films Deposited On Cu Coated Glass Substrates At Low Temperature

In recent years, gallium nitride (GaN) has a wide range of applications in light emitting diodes (LEDs), laser diodes (LDs), ultraviolet (UV) photodetectors and some electronic devices, because it has excellent structural, optical and electrical properties. Although the fast and astonishing developments of GaN-based devices, there are still many problems that hamper further progress. As is known, the performance of GaN-based devices is highly dependent on the substrate materials. Currently, devices of the GaN based materials are usually grown on sapphire (α-Al2O3), Si or SiC substrates. However,α-Al2O3substrates have many shortcomings, such as insulation, high hardness, poor thermal conductivity (33W/mK), small size and so on, making their require more complicated manufacturing process for devices. Meanwhile, high costs and high hardness of SiC have hindered its further wider use; Si with high absorptivity limits the GaN-based LEDs’light output in spite of it is low cost, large-area, relatively good thermal conductivity and electrical conductivity. Compared with α-Al2O3, Si and SiC, metal substrates exhibit some merits, such as good electrical conductivity, superior thermal conductivity, low cost, large-area, high reflectivity and so on. Therefore, metal substrates can not only enhance the heat dissipation efficiency of GaN-based devices, they can also be used directly as the electrodes of an LED. In addition, metal substrates can play a role in reflection, further improving the brightness of LED. Consequently, some research groups have reported the transfer prefabricated GaN films from sapphire substrates onto Cu substrates using thin film laser lift-off (LLO). But this manufacturing process is relatively complicated, and can cause some damage affecting the performance and yield of the devices. Therefore, depositing GaN films directly on metal substrates is a technology that has been strongly demanded.At present, there are already several reports for GaN films deposited directly on metal substrates, such as single crystalline Cu, Ag, Fe, Mo and polycrystalline W, Ta, Nb substrates. The deposition methods mainly include metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE) and pulsed laser deposition (PLD). But the high deposition temperature of MOCVD and MBE may cause harmful interface reactions between the GaN films and the metal substrates, and the stress generated due to thermal expansion coefficient mismatch will degrade the film properties. We carried out the experiment by electron cyclotron resonance plasma enhanced metal organic chemical vapor deposition (ECR-PEMOCVD). With the application of ECR, more activated N can be achieved in the condition of low pressure, which can greatly reduce the deposition temperature of GaN films. Moreover, compared with single-crystal metal substrates, the application of Cu/Glass substrates can greatly reduce the production cost.In this study, the GaN films were deposited using ECR-PEMOCVD system. The Cu/Glass was used as substrates. The Cu/Glass substrates were prepared by RF magnetron sputtering. Trimethyl gallium (TMGa) and high purity N2were employed as Ga and N source materials, respectively. Reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD), atomic force microscopy (AFM), room temperature photoluminescence (PL) and current-voltage (I-V) characteristic measurement were employed to characterize the samples. The results demonstrated that the deposition temperature and the flow rate of TMGa prominently influenced the properties of GaN films, and the quality of GaN films is better crystallized at400℃with TMGa flow rate of1.4sccm.