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

Abstract

The size and emission wavelength of self-assembled InAs/ InP͑001͒ quantum wires (QWrs) is affected by the P / As exchange process. In this work, we demonstrate by in situ stress measurements that P / As exchange at the InAs/ InP interface depends on the surface reconstruction of the InAs starting surface and its immediate evolution when the arsenic cell is closed. Accordingly, the amount of InP grown on InAs by P / As exchange increases with substrate temperature in a steplike way. These results allow us to engineer the size of the QWr for emission at 1. InAs/ InP quantum wires (QWrs) or quantum dots (QDs) are very promising for optoelectronic devices operating in the 1.30-1.55 m wavelength range employed in fiber optical telecommunications systems. 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, 5-15 a deeper understanding of this process is still needed since it determines the size of the nanostructures, governing their emission wavelength.In this work, we have carried out in situ and in real-time stress measurements on an InAs(001) surface exposed to a P 2 flux at different substrate temperatures T s in order to quantify the P / As exchange effect. We have observed a strong dependence on T s of the amount of InP formed (that is, grown without In delivering) during P 2 exposure in the 330-515°C range. We prove that this behavior is directly related to the InAs surface reconstruction, which depends on temperature for a fixed arsenic pressure. Finally, we show that such InAs/ InP surface dynamics can be used to engineer the size distribution of the nanostructures ensemble. To demonstrate this capability, we have studied the optical properties of the InAs QWr as a function of the growth temperature of the InP cap layer, T C . A redshift of the photoluminescence (PL) spectrum is observed as the T C decreases. The size reduction responsible for the observed change in emission energy has been directly demonstrated by transmission electron microscopy (TEM).The P / As exchange process has been assessed by in situ and in real-time measurements of the stress evolution during P 2 exposure of an InAs (001) surface through the optical monitorization of the substrate curvature. This in situ technique provides a direct measurement of the film accumulated stress, ⌺ (stress integrated along the layer thickness). 4 We have used thinned ͑175 m͒ InAs substrates, elongated along the [110] axis to detect stress variations in this direction, in which the whole amount of incorporated InP can be quantified. 5 The phosphorous and arsenic beam equivalent pressures (BEPs) used in these experiments were BEP͑P 2 ͒ = 2.37ϫ 10 −5 mbar and BEP͑As 4 ͒ = 0.53ϫ 10 −5 mbar. Simultaneous reflectance...

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

“…In fact, we can attribute the emission peaks P1-P4 to QWRs with heights of 8, 9, 10, and 11 ML, as done in previous works on InAs QWRs grown on InP buffers. 12 This observation confirms that the optical and the structural properties of the present sample are not affected by the presence of the InGaAs sacrificial layer below the QWRs. About the integrated optical intensity, all the peaks are not affected by temperature in the same way.…”

“…19,20 This result can be compared with structural characterization studies: many elongated QWR defects sometimes more than 500 nm long (zones where the height is different than the average) are typically measured by AFM characterization. 12 Along the QWRs, there are also observed width fluctuations extending 100-150 nm in average. By considering the emission energy differences between the different families, we can estimate localization energies in the order of 30 meV for height fluctuations around 1 ML, while we expect localization energies close to 12 meV considering the inhomogeneous broadening produced by the wire width fluctuations.…”

Size and emission wavelength control of InAs∕InP quantum wires

“…This is partly due to the intrinsic peculiarities associated with the interface between III-V A / III-V B compounds: on one hand, an asymmetric stress appears at the InAs/ InP interface; 4,5 and on the other hand, complicated V A /V B exchange processes take place during epitaxial growth. 6,7 Both intrinsic properties have a strong influence on the nanostructures formation. So, the stress distribution is responsible for the final shape of the nanostructures, resulting either QWr ͓for InAs grown on InP͑001͒ by molecular-beam epitaxy ͑MBE͔͒ 4,5 or QD ͓for InAs grown on InP͑311͒B͔.…”

In As ∕ In P single quantum wire formation and emission at 1.5μm

“…A multimodal hypothesis can explain this behavior assuming that each band corresponds to QWRs or quantum wells ͑QWs͒ of a given constant height. 11,13 Figure 2͑b͒ contains theoretical predictions and experimental data for both InAs/ InP QWRs studied before by the authors, 13 and InAs/ InP strained QWs grown and characterized by Hopkinson et al 22 The solid lines represent the expected energy dispersion as calculated by the respective authors. We start associating the lowest energy band in the spectrum of Fig.…”

“…[6][7][8][9][10] Depending on the wire size and composition, emission tuning capability in the 1.2-1.9 m range has been demonstrated, and both continous wave and time-resolved optical characterizations have been performed on high density QWR arrays. [11][12][13][14] In such situation, long wavelength emission from single QWRs would be desirable. However, for the time being, single quantum wire optical spectroscopy has been restricted mainly to GaAs/ AlGaAs nanostructures emitting on the visible range.…”