Optical Properties of Quantum-Wires Grown Using Lateral Composition Modulation Induced by (InP) 1 /(GaP) 1 Short-Period
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Optical Properties of Quantum-Wires Grown Using Lateral Composition Modulation Induced by (InP)1/(GaP)1 Short-Period Superlattices J. D. Song*, J. M. Kim1, and Y. T. Lee1§ Nano-device Research Center, KIST, Seoul 136-791, Korea 1 Dept. of Information and Communications, K-JIST, Gwangju 500-712, Korea *Email: [email protected]; on leaving from Dept. of Information and Communications, K-JIST § Email: [email protected] ABSTRACT The optical properties of quantum wires (QWRs) grown using lateral composition modulation (LCM) were studied by photoluminescence (PL) measurement as a function cryostat temperature (Tcr). 3 stacked arrays of QWRs were formed by sequential growth of ~ 180 Å-thick LCM layers (lateral period : ~ 90 Å) induced by (InP)1/(GaP)1 short-period superlattices, and 200 Å-thick InGaP spacers at the growth temperature of 490 oC. The formation of QWRs was confirmed by a transmission electron microscopy measurement. By the analysis of the dependence of PL intensity and peak energy of the QWRs on Tcr, the origin of higher energy peak (H) and lower energy peak (L) were investigated. While behavior of the H peak is similar to that of an ordered InGaP, the L peak shows the insensitivity of PL peak energy to Tcr. This is attributed to compensation of the bandgap by competition of strain in the QWR region and indicates the L peak is related to the QWRs. Strong dependence of the L peak on the position of polarizer also supports this. Additionally, the PL peak intensity of the L peak has the maximum value not at the lowest Tcr (10 K) but at 50 K, while the H peak decrease continuously as T increases. We introduced the idea of compensation of the thermal expansion coefficient to explain this phenomenon. INTRODUCTION Natural short-period superlattices (SPSs) perpendicular to the growth direction, or lateral composition modulation (LCM) have been reported in the growth of III-V ternary alloy semiconductors [1]. Stringfellow explained these phenomena as a result of phase separation due to a large and positive enthalpy of mixing caused by a difference in lattice constants between binary constituents of the III-V ternary alloy [2]. Similarly, an intentional growth of SPSs along the [0 0 1] growth direction causes self assembled LCM, where two binary materials of the SPSs experience opposite strains on the substrate, and a deviation of period of the SPSs from the
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lattice constant of the substrate (∆T) is greater than a few – approximately 4 % in case of GaP/InP SPSs [3]. It has been known that the period of LCM is in the range of ~ 100 – 200 Å, a composition fluctuation caused by LCM exists ~ 10 % about the average value, and a reduction in band-gap is ~ 100 – 300 meV with respect to a random alloy of equivalent composition [4]. The novelty of LCM induced by SPSs is that it is the most promising way to fabricate an array of quantum wires (QWRs) through strained-related self-organization phenomena. For example, The group at the University of Illinois reported the operation of QWR laser diodes, where mutliQ
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