Application of Diluted Magnetic Semiconductors and Quantum Dots to Spin Polarized Light Sources
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Application of Diluted Magnetic Semiconductors and Quantum Dots to Spin Polarized Light Sources Pallab Bhattacharya1, Sasan Fathpour, Subhananda Chakrabarti, Michael Holub and Siddhartha Ghosh2 1 Solid State Electronics Laboratory, Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109-2122, U.S.A. 2
Department of Electrical and Computer Engineering, University of Illinois at Chicago, Chicago, IL 60607, U.S.A. ABSTRACT The magnetic properties of single and multiple layers of GaMnAs, grown by molecular beam epitaxy, have been investigated for application as spin injector layers in spin polarized lights sources. Curie temperatures, TC, as high as 150K have been measured in 15nm Ga0.95Mn0.05As films and similar results are obtained for multiple thin layers of GaMnAs separated by 5nm thick GaAs layers. We have also investigated the properties of self-organized InMnAs quantum dots buried in a GaAs or GaMnAs matrix. Magnetization measurements indicate TC>300K in the dot heterostructures. Light-emitting diode heterostructures with 150nm Ga0.95Mn0.05As spin injector layers and In0.4Ga0.6As quantum dot active regions were grown and fabricated into 600µm diameter mesa-shaped surface-emitting devices. Polarized light at 1.05µm is observed with an output polarization efficiency of 26% at a record high temperature. INTRODUCTION Diluted magnetic semiconductors (DMS) have been studied over the past decade due to their potential application in spin-based devices [1,2]. Their suitability as spin injector layers in spinpolarized light sources is also being investigated. While most of the reported studies on DMSs are based on II-VI semiconductors, very encouraging results on III-V semiconductor based DMS have been reported in the recent past and in particular, the (Ga,Mn)As [3] and (In,Mn)As [4] alloys. For electronic or optoelectronic spin injection devices, it is desirable to achieve such injection and device operation at room temperature. In uniform (Ga,Mn)As alloys, the reported Curie temperature, TC, is ~60K for Mn content ~5%. With post-growth anneal for 1-2 hours at T~250˚C, TC is increased to 110K due to formation of Mn(Ga)As clusters [5]. Higher values of TC (160K) have been measured in thin layers of GaMnAs [6]. In this context, it is of interest to study the ferromagnetic properties of an active region consisting of DMS quantum dots buried in a non-magnetic matrix. Self-organized InAs or (Ga,In)As quantum dots grown by molecular beam epitaxy (MBE) or organo-metallic vapor phase epitaxy (OMVPE) are near pyramidal in shape with a base dimension of 20nm and height 6-8nm. Typical dot densities are in the range of (5-10)×1010cm-2. Self-organized quantum dots have found applications in optoelectronic devices
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[7-9], and recently we have measured longer spin lifetimes, ~ 50ps, in InAs/GaAs quantum dots [10], compared to similar quantum wells. Polarized light emitters, detectors, and optical interconnects can be used for applications such as optical switching, optica
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