Basic Characterization Of AlGaAs / GaAs Thin Films

Al Ga As, as an important optoelectronic material, has been widely applied in fabricating high-speed electronic devices and infrared detectors. The quality of Al Ga As, especially the surface quality, directly influences the optoelectronic performance of devices. This thesis elaborately researches the growth of high-quality Al Ga As/Ga As heteroepitaxial film by utilizing molecular beam epitaxy(MBE) equipment.Before the growth, we investigated the oxide desorption method of Ga As substrate, the growth mechanism of Al Ga As/Ga As heteroepitaxy and the influence of aluminum content and growth rate on the surface morphology of Al Ga As film. The reflection high-energy electron diffraction(RHEED) and scanning tunneling microscope(STM) were utilized to analyze the film surface. The results indicate that with the increase of aluminum composition, the surface reconstruction transited from a clear(2×4) pattern to an unclear(2×4) pattern. The film surface morphology transited from multilayer island structure to a relatively flat surface(when the composition of aluminum is increased to 25%). With the aluminum composition of the film increasing over 25%, the average size of terrace gradually decreased, and pits started to form on the surface.With the increase of growth rate of Al0.25Ga0.75 As film, whose thickness is 20 monolayers, the surface will become rougher. In addition, as for the morphology of Al0.25Ga0.75 As thin films on Ga As substrate, the faster the growth rate was, the rougher the morphology became. Through statistics of pit coverage and curve fitting, we found that a perfect flat surface could be obtained when the growth rate was 0.13ML/s, which agrees quite well with the STM image of sample with 0.16 ML/s growth rate.The surface morphology of Al0.15Ga0.85As/GaAs films and In0.15Ga0.85As/GaAs films were compared. Although both the GaAs substrates were atomically flat, as the thickness increased, the peninsulas and islands in the In0.15Ga0.85As/GaAs film became smoother and distorted, which could be explained by using the half terrace diffusion model.We also have grown Al Ga As films with different compositions of aluminum and thickness(300nm/600nm) on the flat Ga As surface. XRD were utilized to analyze the crystal structure of the film. The results showed that with the increase of aluminum composition, the crystalline size of the thin film would decrease. The growth trend of grain was increasingly obvious, the growth of high aluminum composition even showed amorphous structure. In addition, After growing the Al0.25Ga0.75As/Ga As multiple quantum well, the PPMS was utilized to test its transport properties. The carrier concentration, Hall mobility were calculated, and meaningful results were obtained.