Stacking of InAs/InP(001) quantum wires studied by in situ stress measurements: Role of inhomogeneous stress fields

Abstract

Size and spatial distribution homogeneity of nanostructures is greatly improved by making stacks of nanostructures separated by thin spacers. In this work, we present in situ and in real time stress measurements and reflection high-energy electron diffraction observations and ex situ transmission electron microscopy ͑TEM͒ characterization of stacked layers of InAs quantum wires ͑QWRs͒ separated by InP spacer layers, d(InP), of thickness between 3 and 20 nm. For d(InP)Ͻ20 nm, the amount of InAs involved in the created QWR from the second stack layer on, exceeds that provided by the In cell. Our results suggest that in those cases InAs three dimensional islands formation starts at the P/As switching and lasts during further InAs deposition. We propose an explanation for this process that is strongly supported on TEM observations. The results obtained in this work imply that concepts like the existence of a critical thickness for two-to three-dimensional growth mode transition should be revised in correlated QWR stacks of layers. © 2004 American Institute of Physics. ͓DOI: 10.1063/1.1759374͔The incorporation of nanostructures in electronic and optoelectronic devices provides properties improvement and design possibilities, yet requiring the control of their size and position. For self-assembled nanostructures, the size homogeneity and spatial distribution can be greatly improved by stacking several layers. [1][2][3][4] In this context, the vertical stacks of self-assembled InAs quantum wires ͑QWRs͒ grown on InP͑001͒ are of particular interest for lasers, as they emit light at 1.30 and 1.55 m. [5][6][7] In stacks of nanostructures, the buried ones produce inhomogeneous strain fields that propagate toward the capping layer surface where the next nanostructures will be formed. 1,2 This leads to a vertical correlation between the nanostructures layers depending both on the size of the buried nanostructures and the spacer layer thickness.In this work, we have studied the growth of multilayers of InAs QWRs with different spacer layer thicknesses, d(InP), by in situ and in real time stress measurements and reflection high-energy electron diffraction ͑RHEED͒. A strong influence of the spacer layer thickness on QWR formation process in the second and successive layers of the stack has been observed: QWRs are correlated for d(InP)Ͻ20 nm, where a reduction of the amount of deposited InAs necessary for QWR formation ͑observed by RHEED͒ together with an increase in InAs growth rate ͑ob-tained from stress measurements͒ take place. In order to explain these results, we propose a model that is strongly supported by transmission electron microscopy ͑TEM͒ images. Our experiments provide quantitative values of the extra amount of material involved in the formation of vertically correlated self-assembled nanostructures, as well as the evidence of the absence of a two-dimensional ͑2D͒-threedimensional ͑3D͒ growth mode transition as the relevant process in nanostructures self-assembling during stacking.The samples under study consist of...

Size and emission wavelength control of InAs∕InP quantum wires

“…In fact, the InAs QWr can be formed by As/ P exchange after a long-time exposure of an InP surface to an arsenic flux even without indium deposition. 9,13 C. Size control by changing the InP cap layer growth temperature Figure 4 shows the PL measurements in samples of series C, where we used different substrate temperatures ͑T cap ͒ during InP cap layer growth. We see that the measured PL spectrum shifts to shorter wavelengths as T cap increases from 380 to 515°C.…”

“…For example, the exchange processes are temperature dependent 6,7 and they are also influenced by the strain distribution at the growth front. 9 Thus, if appropriately controlled, they can be used as a design tool for the emission wavelength. Our aim in this work is to study different ways of controlling the size of MBE-grown InAs/ InP͑001͒ QWrs, establishing procedures to engineer the emission wavelength of these nanostructures.…”

Localization effects on recombination dynamics in InAs/InP self-assembled quantum wires emitting at 1.5 μm

“…The InAs nanostructures were formed by the Stranski-Krastanov method depositing 1.7 monolayers (MLs) of InAs at a substrate temperature of 515 C with a growth rate of 0.1 ML/s. Due to the anisotropic character of the elastic relaxation in this system, QWRs arrays are naturally arranged along the [1][2][3][4][5][6][7][8][9][10] crystal direction as explained elsewhere. 9 Figure 1 shows an atomic force microscopy (AFM) image of an uncapped sample which exhibits a typical QWR width and height of 11 and 3.2 nm forming quasi-periodic structures (with pitch period around 18 nm).…”

Size control of InAs∕InP(001) quantum wires by tailoring P∕As exchange

“…In this case, the amount of InP formed will be even larger than that obtained in plain InAs surfaces, as the P / As exchange will be enhanced by the strain. 6,7 The effects produced by the P / As exchange can be beneficial to adjust the QWr size for a predetermined emission wavelength. Figure 2 shows the 12 K PL (continuous line) and 300 K (dotted lines) spectra of the first series of samples studied (one layer of QWr capped by InP grown at LT, MT, and HT regions).…”

“…1-3 However, these nanostructures have not been as extensively exploited as InAs/ GaAs QD partly due to the intrinsic peculiarities of the interface between III-V A / III-V B compounds: On one hand, an asymmetric stress appears at the InAs/ InP interface; 4 on the other hand, complicated V A /V B exchange processes take place during epitaxial growth. Although P / As exchange has been widely studied, [5][6][7][8][9][10][11][12][13][14][15] a deeper understanding of this process is still needed since it determines the size of the nanostructures, governing their emission wavelength.…”