Low-temperature growth of polycrystalline GaN films using modified activated reactive evaporation

摘要

We report the preparation of polycrystalline GaN films on glass substrates by modified activated reactive evaporation (MARE). In this technique, substrates are kept on cathode instead of ground electrode and hence subjected to low-energy nitrogen ion bombardment. With increase in rf power, nitrogen to gallium (N/Ga) ratio in the films and film resistivity monotonically increases whereas ' oxygen impurity reduces. All GaN films are of wurtzite structure and films grown at higher powers have preferred orientation towards c-axis. Crystalline quality improves with increase in rf power up to ～150W and thereafter it degrades. Improvement in crystalline quality can be attributed to Ga/N stoichiometry and reduction in oxygen concentration, whereas degradation can be attributed to the presence of point defects due to excess nitrogen and nitrogen ion bombardment. Optical emission spectroscopy (OES) is used to investigate the relative concentration of excited species during GaN growth. MARE offers a technique to grow low-temperature group III nitride semiconductors. A high deposition rate (4.3μm/h) was achieved in MARE for growing polycrystalline films on relatively inexpensive substrates. MARE is relatively less complex and offers a viable alternative for large scale growth for polycrystalline GaN thin films.