The Study Of The Influence Of The Gan Thin Film Dislocations On The Carrier Properties

The effect of threading dislocation density (TDD) in GaN thin films, which were grown on the sapphire (α-Al2O3) substrate by metal organic chemical vapor deposition (MOCVD), was studied in this paper. Firstly, different GaN thin films were grown with different parameters in order to achieve the different TDDs, and some sample was treated by the rapid treating progress (RTP) to make different TDDs in the same sample. Then, the TDDs and optical and electrical character of GaN samples were measured by double-crystal X-ray diffraction (DCXRD) photoluminescence (PL),Hall measurement and transmission electron microscope (TEM). The TEM was used to investigate the TD distribution and developed. The TDDs were in the magnitude of 108cm-2 calculated by DCXRD, and then based on these results the relationship between the TDDs and properties of carrier and photo-electricity of GaN.Through the relationship curves between TDDs and carrier concentration or mobility of GaN samples, it was noticed that the carrier concentration increased with the TDDs increasing, while the mobility was contrary. The reasonable explanation was achieved by analyzing the possible factors that influence carrier concentration and the mobility. Because of the crystal distortion near the dislocation lines, the energy is so high that shallow-donor defects in the GaN crystal can be captured on or near the dislocation lines, which may cause the high background carrier concentration. So, with the increasing TDDs, the carrier concentration increased. At the same time, there is the potential energy around the dislocation lines and the dispersion effect depresses the carrier mobility. For that reason, the carrier mobility decreased, while the TDDs increasing and had monotony in the scope of 108cm-2 of TDDs.To discover the performance change caused by the carrier with the TDDs change, the optical and electric property of GaN samples were measured by PL and Hall. It was found that the ratio between the yellow light emission intensity and band emission intensity (IYL/Io)) was highest in the sample with the least TDDs. In all other samples, with the increasing of the TDDs, the band emission intensity decreased gradually, while the yellow light emission intensity increasing, and the same result was found in one sample with different TDDs achieved by RTP in two temperatures. On the other hand, the TDDs in GaN samples may form the low resistance ohm channels, and lead carrier moving along the TDD lines, which caused the resistance ratio of GaN samples decreased with TDDs increasing.