Photoluminescence and In/Ga Intermixture in InAs/InGaAs DWELL Structures
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Photoluminescence and In/Ga Intermixture in InAs/InGaAs DWELL Structures A. Vivas Hernandez1, I.J. Guerrero Moreno2 and E. Velázquez Lozada1 1 2
ESIME– Instituto Politécnico Nacional, México D. F. 07738, México
UPIITA– Instituto Politécnico Nacional, México D. F. 07320, México E-mail: [email protected] , [email protected]
ABSTRACT The photoluminescence (PL) and photoluminescence temperature dependences have been studied in InAs quantum dots (QDs) embedded in the In0.15Ga1-0.15As/GaAs quantum wells (QWs) with QDs grown at different temperatures (470-535 oC). Ground state (GS) related QD PL peaks shift into the red side with increasing QD growth temperature to 510 oC and the blue shift is observed when the temperature increased to 535 oC. The temperature dependences of GS PL peak positions were fitted on the base of Varshni relation and the fitting parameters were compared with the bulk InAs and the In0.21Ga0.79As allow. This comparison has revealed that for QDs grown at 490-510 oC the PL fitting parameters are the same as for the bulk InAs crystal. The DWELL structures with QDs grown at other temperatures have fitting parameters different from the bulk InAs. Last fact testifies that in these structures the Ga/In inter-diffusion between QDs and a QW has been realized. This Ga/In intermixture can be stimulated not only by the high temperature (535 oC), but by the essential elastic stress as well in the DWELL structure with lower QD densities. INTRODUCTION Self-assembled InAs QDs embedded into the InGaAs/GaAs quantum wells are very interesting object for fundamental physics and as an active medium for semiconductor lasers for optical fiber communication [1], infrared detectors [2,3] memory devices [4] and photo-diodes [5-7]. The fabrication of low-dimensional semiconductor structures, as InAs quantum dots, have become more reliable enabling systematic studies [1]. It was shown earlier [8] that the InAs QD density and size strongly depend on QD growth temperatures [9-11] and on a composition of capping/buffer InGaAs layers [12, 13]. In symmetric quantum wells with the same composition of In0.15Ga0.85As of capping and buffer layers the density of QDs decreases and their size increases monotonically with the enlargement of QD growth temperatures [8,10]. The decrease of QD density and the enlargement of QD sizes permit to expect decreasing of PL intensity and shifting of peak positions monotonically. However the PL intensity and peak positions of QD ground states (GS) have changed non monotonically: at low QD growth temperatures (470-510 o C ) the PL peak shifts from 1.24 µm to 1.30 µm, but for higher QD growth temperatures (510535 oC) the PL peak shifts again to 1.20 µm [8,10] . It is know that the PL peak position at 1.30 µm in laser structures is important because it corresponds to the transparency window of optical fibers. Three different factors can influent on GS peak positions in studied DWELL structures: i) QD size parameters, ii) Ga/In inter-diffusion, that influent on QD material composition, and ii
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