Surface modification of InGaAs/GaAs heterostructures by swift heavy ion irradiation

摘要

We investigate the surface morphology of molecular beam epitaxy (MBE) grown InGaAs/GaAs(001) heterostructures using atomic force microscope (AFM) before and after irradiation. Samples with layer thicknesses below critical layer thickness (i.e. fully strained) have smooth surface where as, the samples grown beyond critical layer thickness have cross hatch patterns at the surface. The transition from smooth to cross-hatch pattern may be used to identify the onset of strain relaxation. The samples were subjected to swift heavy ion (SHI) irradiation using 150 MeV Ag~(12+) ions with a fixed fluence of 1 x 10~(13) ions/cm~2. The morphology of the strained samples was almost similar before and after irradiation where as, the partially relaxed samples were observed to have variations. The electronic energy loss of the incident ions which is dominant compared to the nuclear energy loss is effective to modify with the fluence used in the present study for partially relaxed samples. The relaxation of excited electron subsystem of the target results in the melting and re-growth which reflects in the surface morphology. The observed modifications at the surface may be attributed to (ⅰ) irradiation induced surface mass transport and (ⅱ) interface modifications, where both these factors determine the surface morphology of heterostructures. The effects of irradiation on the surface and interface of the samples have been realized by AFM studies.