book of abstracts - IM2NP

A B S T R A C T S THURSDAY, JULY 1 N A N O S E A 2 0 1 0
10H00-10H20
Self-assembled InAs quantum dots embedded into GaAs with different strain
reducing layers exhibiting strong photo- and electroluminescence in 1.3 and
1.55 μm bands.
P. Hazdra1, J. Oswald2, V. Komarnitskyy1, K. Kuldová2, A. Hospodková2, E.
Hulicius2 and J. Pangrác2 (1Department of Microelectronics, Faculty of Electrical Engineering, Czech
Technical University in Prague, Technická 2, CZ-16627 Prague 6, Czech Republic, 2Institute of Physics of the AS
CR, v. v. i., Cukrovarnická 10, 162 53 Prague 6, Czech Republic). hazdra@fel.cvut.cz
Investigation of self-assembled InAs quantum dots (QD) in GaAs is motivated by the demand for highspeed,
low cost, low pumping power and temperature stable lasers for 1.3 or 1.55 μm optical communication
bands. Embedding of QDs in a functional structure can be optimized by covering them with a thin strain
reducing layer (SRL) which modifies the QDs shape and composition, as well as composition of surrounding
barriers, leading to changes of electronic structure and emission wavelength.
In this paper, we report about self organized InAs QDs embedded in GaAs using low temperature grown
InGaAs or GaAsSb SRLs. The structures were prepared on GaAs substrates by low pressure metalorganic
vapour phase epitaxy (MOVPE). The RAS (Reflectance Anisotropy Spectroscopy) LayTec equipped
AIXTRON 200 reactor and the Stranski–Krastanow growth mode at 490°C was used for sample preparation.
TMIn, TMGa and AsH3 were used as precursors for samples with InxGa1-xAs SRLs; TEGa, TMIn, TBAs
and TESb for structures with GaAs1-ySby SRLs. For QD formation, the growth was interrupted for 15 s
after the formation of 2 ML of InAs. While RAS was used for in-situ growth monitoring, grown QD
structures by were characterized using atomic force microscopy (AFM) and X-ray diffraction. Photo- (PL)
and electroluminescence (EL) was used for monitoring of optical properties. Analysis of PL and AFM data
was supported by numerical simulation of QD electron states.
Results show that a proper In0.23Ga0.77As SRL narrows a broad PL spectrum of uncovered QDs (4 6 nm
high InAs lenses) and causes a red shift of its maximum up to 1.55 µm. Analysis of measured data showed
that this is affected both by the change of the barrier and by the increase of the height of the overgrown QDs.
In the case of GaAsSb SRL, the red shift is smaller since the QD size is preserved but not increased. Higher
Sb content increases the red shift due to gap alignment modification, however, at 19% of Sb in SRL, the
QD/SRL heterojunction type changes from type I to type II and PL efficiency decreases due to smaller
overlapping of electron and hole wave functions. EL characteristics of InAs QD structures successfully
embedded in functional PiN diodes will be presented, as well.
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