Scanning tunneling microscopy and spectroscopy of arsenic antisites in low temperature grown InGaAs

Scanning tunneling microscopy is used to study low temperature grown (LTG) InGaAs, with and without Be doping. The Be-doped material is observed to contain significantly fewer AsGa antisite defects than the undoped material, with no evidence found for Be-As complexes. Annealing of the LTG-InGaAs forms precipitates preferentially in the undoped material. The previously observed dependence of the optical response time on Be-doping and annealing is attributed to changes in the As antisite concentration and the compensation effect of the Be. Low temperature grown (LTG) III-V semiconductor materials are known to contain excess arsenic. This change in the stoichiometry leads to several interesting properties such as a fast absorption recovery time or a high resistivity when the materials are subsequently annealed. Although most of the LTG semiconductor materials studies to date have been performed on GaAs, the possibility of producing devices having a subpicosecond return to equilibrium dynamic in the 1.55 μm wavelength region has produced a growing interest in LTG-InGaAs and InGaAs/InAlAs multiquantum well structures.[1,2] Compared to LTG-GaAs, the concentration of As-based deep centers is smaller in LTG-InGaAs,[3] resulting in a longer absorption recovery time in undoped material.[4] When LTG-InGaAs is doped with beryllium, the photoexcited free-carrier lifetime becomes shorter and comparable to that of LTG-GaAs (subpicosecond electron lifetimes have been observed [5]). Whereas annealing of undoped material is found to dramatically slow the absorption recovery time,[6] Be doping maintains the fast recovery time. To explain this effect, the presence of midgap states has been proposed, arising from complexes between Be dopants and the excess As introduced during growth.[1,2,4,5] The direct compensation effect of the Be has also been suggested.[4] In this work, we report a study of undoped and Be-doped LTG-InGaAs layers by scanning tunneling microscopy and spectroscopy. The scanning tunneling microscope (STM) has been previously used to observe defects in LTG-GaAs.[6] As for that case, we observe in LTG-InGaAs the presence of arsenic antisites. We find a significantly lower concentration of antisites in the asgrown Be-doped material compared to the undoped material (with the difference being much great-