Al2O3/HfO2 composite films were deposited on GaAs substrates with different aspect ratios by thermal atomic layer deposition (ALD). Through the analysis of surface and energy dispersive spectrum(EDS), it is found that the deposition temperature has a great influence on the molar ratio of the composite films. With the increase of the aspect ratio, there are residues on the surface and in the grooves. With the increase of the ALD deposition temperature, the residues on the surface and in the grooves decrease, the mole ratio tends to be uniform. When the aspect ratio is 22, using the low deposition temperature of 150 ℃, there are basically no residues on the surface and in the grooves. However, when the aspect ratio is 425, there is a large amount of residues. Only when the temperature rises to 300 ℃, the residues on the surface and in the grooves can be obviously eliminated. ALD technology can realize all-round passivation of various device structures, which is unmatched by other chemical vapor deposition (CVD).