Chemical Effects in Ion Implantation Induced Quantum Well Intermixing
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CHEMICAL EFFECTS IN ION IMPLANTATION INDUCED QUANTUM WELL INTERMIXING Todd W. Simpson, Paul G. Piva, Ian V. Mitchell University of Western Ontario, Department of Physics & Astronomy, London, ON, N6A 3K7, CANADA ABSTRACT Ion implantation followed by rapid thermal annealing is used to induce layer intermixing and thus selectively blue-shift the emission wavelength of InP-based quantum well heterostructures. The intermixing is greatly enhanced over thermal intermixing due to the supersaturation of defects. The magnitude of the observed blue-shift has been studied previously as a function of ion fluence and ion mass: the dependence on ion mass is well established, with heavier ions producing a larger shift. We show here that chemical effects can also play a significant role in determining the induced blue-shift. Data are presented from the implantation of the similar mass ions; aluminum (m~27), silicon (m~28) and phosphorus (m~31). The Pinduced blue shift displays a monotonic increase with fluence, consistent with previous studies; however, the fluence dependence of Al- and Si-induced blue-shifts both deviate significantly from the behaviour for P. These results have important implications for attempts to scale intermixing behaviour with ion mass. INTRODUCTION Ion implantation induced quantum well intermixing (QWI) is a post-growth technique for modifying the bandgap energy of quantum well heterostructures [1]. Mobile defects, created during implantation, enhance diffusion of constituent atoms across the quantum well/barrier interface during subsequent thermal annealing. The nominally square wells are broadened by interdiffusion and the corresponding band gap is increased. Photo luminescent (PL) emission of implanted and subsequently annealed structures is therefore blue-shifted relative to un-implanted regions of the wafer. The magnitude of this shift in GaAs/AlGaAs quantum well structures has been shown to increase with ion mass and this dependence has been associated with the number of point defects created per ion [2]. In this paper, we investigate the role of ion mass in the intermixing of an InGaAs/InGaAsP structure. The PL wavelength shift is used to semiquantitatively characterize the release of defects from the surrounding InP. The role of chemical effects in the induced blue-shift is investigated through a comparison of Al, Si and P ion implantation. In the case where a shallow implant is performed to confine the damage to the InP layer above the multiple quantum well (MQW) structure, defects are released from the implant region during annealing and diffuse to the MQW region. It is the diffusing defects that enable the interdiffusion of the well and barrier materials. It is believed that intermixing in the absence of implant damage, the so-called “thermal-only” shift, is driven by native defects, presumably incorporated during initial growth of the structure. The concentration and nature of these native defects depends on the growth method (CBE, CVD, MBE) and on the processing temperature during growth [3]. Th
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