Anomalous defect structure formed on GaSb surface by low temperature Sn ion-implantation and its formation mechanism

Defect formation in (100) GaSb by 60 keV Sn+ ion-implantation at 150-153 K is investigated using cross-sectional TEM, SEM and EDX. An anomalous struct ure consisting of many cells, which Looks like a honey comb, was formed on the surface implanted with 8 x 10(18) ions/m(2). The diameter and the depth of a cell were about 50 nm and 220-250 nm respectively, and the thickness of the walls partitioning the cells was about 10 mm. The upper part of the partitioning wall is amorphous and rich in Ga, while the lower part shows c rystalline structure. A heavy strain region with 50 nm thickness, correspon ding to the maximum depth of the projected Sn ions, was observed under the cells. This defect structure is compared with similar defects which have be en observed by other researchers. The defect formation mechanism is discuss ed, and an explanation based on movement of the implantation induced point defects is proposed. It is assumed that hills and hollows are formed in the early stage of implantation. The point defects created on the hills do not contribute to the development of the defect structure, because they annihi late almost completely by the recombination of vacancy and interstitial and by the movement to the near surface sink. However, under the hollows, vaca ncies remain which escaped recombination, and the Interstitial atoms, which are highly mobile at low temperatures, migrate far from there to aggregate under the hills. The hollows become deeper by the movement of the remainin g vacancies to the surface, and the hills develop into the walls by the mig ration of the interstitial atoms from the surrounding hollows.