Photoluminescence of multi-layer GeSi dots grown on Si (001)
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Photoluminescence of multi-layer GeSi dots grown on Si (001) J. Wan, Y. H. Luo, G. L. Jin, Z. M. Jiang, J. L. Liu, X. Z. Liao,1 J. Zou,1 and Kang L. Wang Device Research Laboratory, Electrical Engineering Department University of California at Los Angeles, Los Angeles, CA 90095-1594, U.S.A. 1 Australian Key Center for Microscopy & Microanalysis, The University of Sydney, Sydney NSW 2006, Australia ABSTRACT Temperature and power dependent photoluminescence measurements were carried out on the multi-layer structure of GeSi dots grown on Si(001) substrate by gas-source molecular beam epitaxy. The transfer of photon-induced carriers from wetting layers into the dots and the region near the dots was evidenced. Different power dependent behaviors of the photoluminescence peak position were observed for the dots and the wetting layer. Accordingly, type-II and type-I band alignments were proposed for the dots and the wetting layers, respectively. After annealing, the photoluminescence peaks from the dots and the wetting layers showed blueshift due to the atomic intermixing. For the samples annealed at temperature above 850oC for 5min, the band alignment of the dots changes from type-II to type-I. INTRODUCTION Recently many studies have been done on the growth mechanism, electrical and optical properties of GeSi dots embedded in Si [1-3] due to its potential applications, such as optoelectronics. Although photoluminescence (PL) from GeSi dots has been widely studied, little has been done on the band alignment and the correlation between the PLs from the dots and the wetting layers, which is an inevitable result of the Stranski-Krastanow growth mode upon reaching a strain-defined critical thickness [3]. In addition, from a practical point of view, it is desirable to confine both electrons and holes within the dots for many potential applications, such as quantum dot based laser, single electron transistor and quantum computer [4]. However, the band alignment between the GeSi dots and Si matrix is type-II structure and the electron could not be trapped into the dots directly. In this paper, both excitation power and temperature dependent PL spectra of the GeSi dots and the wetting layers were measured. The band alignment of the GeSi dots and the wetting layer was studied. In addition, the annealing effect on the band alignment of the GeSi dots was also investigated. EXPERIMENTAL DETAILS The sample was grown on Si (001) substrate by gas-source molecular beam epitaxy (GSMBE) with a Si2H6 gas source and a Ge effusion cell. Ten layers of GeSi dots seperated by Si spacer layers were grown at the temperature of 575oC. The thickness of the Ge dot layer and the Si spacer layer was 1.6 and 40 nm, respectively. Although pure Ge atoms were deposited during the dots growth, the dots are GeSi alloy, as discussed later. Pieces of the sample were annealed for 5 min with temperatures varied between 650 and 900oC by a step of 50oC using rapid thermal annealing in nitrogen gas ambient. The PL measurements were performed by excitation of an Ar+
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