Manganese diffusion in ingaas/gaas quantum well structures

Abstract

508Heterostructures with InGaAs/GaAs quantum wells containing a manganese delta layer in the GaAs cap layer are promising materials for the development of spin electronics elements, in particular spin light emitting diodes [1]. Investigations of the photolumi nescence, photoelectric, and electrical properties of these structures have previously been reported [2,3]. The formation of devices based on these heterostruc tures implies the application of annealing, e.g., in the preparation of metal contacts. Furthermore, anneal ing can be used as an additional after growth treat ment improving the crystal quality of heteronano structures and causing an increase in their Curie point. The main condition determining the choice of the optimal annealing temperature is the study of manga nese diffusion in these heteronanostructures.In order to perform such studies according to an original method combining MOC hydride epitaxy and laser deposition, we have grown structures with three InGaAs/GaAs quantum wells and a Mn delta layer [4]. Quantum wells with a width of 5.2, 7.8, and 7.8 nm and an In concentration of 22% (QW1), 27% (QW2), and 33% (QW3), separated by 24 nm GaAs spacer layers (the spacer between the delta layer and QW3 was 4 nm thick), were formed by MOC hydride epitaxy at a temperature (T g ) of 550°C. The delta layer with a Mn content of 0.12 monolayer (ML) and the GaAs cap layer with a thickness of 30-40 nm were formed by laser deposition at T g = 400°C. The structures were subjected to isochronal annealing for 30 min in nitrogen flow in the temperature range from 325 to 700°C with a temperature step of 25°C. The samples were placed on GaAs substrates in a graphite holder with their front side down on the substrate sur face. After annealing the light emitting properties of the structures were examined by photoluminescence spectroscopy at 77 K. A 30 mW He-Ne laser with a wavelength of 632.5 nm was used to excite the emis sion. The diffusion of the Mn impurity was controlled by profiling the elemental composition of the initial and annealed samples using secondary ion mass spec trometry (SIMS) with a TOF.SIMS 5 installation. Layer by layer analysis was carried out with the use of O 2 or Cs sputter ion beams and a Bi analysis ion beam. The depth and sizes of the etching craters were measured by a Talysurf CCI 2000 interference micro scope [5].The photoluminescence spectrum (Fig. 1) of the initial sample contains three peaks corresponding to three quantum wells with a quantum energy of 1.363 eV (QW1), 1.277 eV (QW2), and 1.220 eV (QW3). It is Abstract-Manganese diffusion during annealing of structures with InGaAs/GaAs quantum wells and a Mn delta layer is investigated by photoluminescence and secondary ion mass spectrometry. Annealing at 365-425°C results in quenching of the photoluminescence intensity for the quantum well nearest to the Mn delta layer, due to Mn diffusion into the quantum well. The penetration of Mn and In into the GaAs coating/cover layer is discovered. Near the surface the profiles of these elements...

Quantifying Mn Diffusion through Transferred versus Directly Grown Graphene Barriers

“…A similar behavior is observed for transferred graphene/GaAs compared to that for bare GaAs. To benchmark the accuracy of our method, we find that our experimentally determined diffusivities for Mn on bare GaAs (Figure b, filled black circles) are in good agreement with previous experiments (open black circles). − …”

“…(b) Diffusivity vs inverse temperature for Mn/GaAs (black) and Mn/layer-transferred graphene/GaAs (blue). The open symbols represent previously reported diffusivity for Mn on GaAs (no graphene) from refs –. (c) Schematic diffusion processes.…”

Quantifying Mn diffusion through transferred versus directly-grown graphene barriers

“…4(b), filled black circles) are in good agreement with previous experiments (open black circles)[16][17][18].…”

“…(b) Diffusivity vs inverse temperature for Mn/GaAs (black) and Mn/layer transferred graphene/GaAs (blue). The open symbols represent previously reported diffusivity for Mn on GaAs (no graphene) from Refs [16][17][18]…”