Microstructure evolution in low-temperature, ion-implanted Al{sub x}Ga{sub 1-x}As.

The accumulation of ion implantation damage in Al{sub x}Ga{sub 1{minus}x}As/GaAs heterostructures (0 {le} x {le} 0.85) at 77 K has been investigated by using a combination of RBS (at 77 K and 293 K) and TEM (at 293 K). Recovery, as seen by a decrease in the channeling yield, occurs on warming to room temperature unless the material has been driven amorphous or x {ge} 0.85. Depending on the implantation condition, the recovered structure consists of either planar defects or dislocation loops. Planar defects were also observed in alloys with x = 0.85, although they were confined to a narrow band that separated the amorphous from the crystalline material. By implanting with ions of different energy it was shown that amorphization can initiate within the layer away from the interfaces, showing that interfaces are not needed for amorphization. Implantations with 500 keV Krions were performed at 50 K in-situ in the Intermediate-Voltage Electron Microscope--Accelerator facility at Argonne National Laboratory. Planar defects were produced on warmup, showing that they are not necessary for amorphization. We propose that amorphization initiates because of an accumulation of damage and that the dependence of the amorphization dose on Al content is related to differences in cascade dynamics.