Control of Morphology and Substrate Etching in InAs/InP Droplet Epitaxy Quantum Dots for Single and Entangled Photon Emitters

Abstract

We present a detailed atomic-resolution study of morphology and substrate etching mechanism in InAs/InP droplet epitaxy quantum dots (QDs) grown by metal–organic vapor phase epitaxy via cross-sectional scanning tunneling microscopy (X-STM). Two different etching processes are observed depending on the crystallization temperature: local drilling and long-range etching. In local drilling occurring at temperatures of ≤500 °C, the In droplet locally liquefies the InP underneath and the P atoms can easily diffuse out of the droplet to the edges. During crystallization, the As atoms diffuse into the droplet and crystallize at the solid–liquid interface, forming an InAs etch pit underneath the QD. In long-range etching, occurring at higher temperatures of >500 °C, the InP layer is destabilized and the In atoms from the surroundings migrate toward the droplet. The P atoms can easily escape from the surface into the vacuum, forming trenches around the QD. We show for the first time the formation of trenches and long-range etching in InAs/InP QDs with atomic resolution. Both etching processes can be suppressed by growing a thin layer of InGaAs prior to the droplet deposition. The QD composition is estimated by finite element modeling in combination with X-STM. The change in the morphology of QDs due to etching can strongly influence the fine structure splitting. Therefore, the current atomic-resolution study sheds light on the morphology and etching behavior as a function of crystallization temperature and provides a valuable insight into the formation of InAs/InP droplet epitaxy QDs which have potential applications in quantum information technologies.

Self‐Assembled InAs Quantum Dots on InGaAsP/InP(100) by Modified Droplet Epitaxy in Metal–Organic Vapor Phase Epitaxy around the Telecom C‐Band for Quantum Photonic Applications

“…Finally, it is worth pointing out that even though the QDs are not directly formed from the initial droplets as was found for the "standard" DE mode (see, e.g., our previous work on InAs/InP QDs), [12] there is no evidence for the presence of a strained wetting layer, confirmed by the optical characterizations in this work. Additionally, in our previous morphological investigations by XSTM on InAs/InGaAs DE QDs of Figure 5d, [15] we had evidence for the presence of the 5 nm InGaAs interlayer and the QDs nucleated directly on this layer, without the presence of a wetting layer.…”

“…[35] As for the case of QDs on InGaAs, no longrange etch pits around each QD are present. [12,13,15] From these observations, we can conclude that inserting the InGaAs(P) layers results in a modification of the growth kinetics from a mass-transport regime (on bare InP) to a surface reactionlimited regime on the interlayers, as previously suggested in our cross-sectional tunneling microscopy (XSTM) study on InAs QDs on both InGaAs and InP [15] and predicted by Yoon et al [36] Although at the typical droplet temperature of 400 °C the In surface diffusion ρ apparently strongly differs for InGaAs and InGaAsP surfaces, with ρ InGaAs << ρ InGaAsP as discussed above (see also Figure 3 as reference) we observe that, after crystallization, QDs on both layers present a similar density of 1 Â 10 10 cm À2 versus 2 Â 10 10 cm À2 for InGaAs and InGaAsP, respectively (Figure 5c,d). We ascribe this phenomenon to a modification of the surface kinetics triggered by temperature and the As supply during droplet crystallization.…”

“…[10,11] Droplet epitaxy (DE) in metal-organic vapor phase epitaxy (MOVPE) is a recent and very promising approach for QD fabrication, as it combines a large-scale epitaxial technique and a versatile epitaxial method. [12][13][14][15] This is a relatively new process that is not fully understood in terms of growth dynamics, particularly for III-V material systems compatible with telecom wavelengths, such as InAs/InP. Thus, it holds great potential for further development in the fabrication of telecom QDs for a broad range of applications.…”

“…Additionally, using InP as matrix material allows for the growth of InAs quantum emitters without the assistance of any additional metamorphic buffer, such as AlInAs/GaAs. [16][17][18] InAs/InP QDs grown by DE in MOVPE show high symmetry [12,15,19] and consequently lower FSS and longer coherence times compared to their Stranski-Krastanow (SK) counterparts. [18,20] They are thus excellent candidates as high-quality photon sources for photonic devices.…”

Atomic-scale characterization of single and double layers of InAs and InAlAs Stranski-Krastanov quantum dots

“…Quantum dots (QDs) are of great interest as they represent an ideal system to investigate the confinement of carriers in all three spatial dimensions and provide novel properties for many optoelectronic applications such as semiconductor lasers [1], infrared photodetectors [2], intermediate-band solar cells [3], ultrahigh-density optical memories [4], flash memories [5,6], quantum computing and information [7][8][9][10][11], etc. When dealing with solid-state devices, the InAs/GaAs system is often used because homogeneous three-dimensional (3D) InAs islands can be easily nucleated on the GaAs(001) surface using the Stranski-Krastanov (SK) growth mode which involves the strain-induced formation of 3D islands due to the lattice mismatch between the two materials [12].…”