Impact of an In_xGa_1–xAs Capping Layer in Impeding Indium Desorption from Vertically Coupled InAs/GaAs Quantum Dot Interfaces

Abstract

This study describes the effect of a thin GaAs spacer of 4.5 nm thickness in a bilayer-coupled InAs quantum dot (QD) heterostructure. Here, we report the first demonstration of InAs/GaAs QDs capped by self-assembled In x Ga1–x As layers. Self-assembled In x Ga1–x As layers were introduced into each intermediate layer across the interface of InAs QDs and the GaAs layer in a vertical-coupled bilayer QD (VCBQD) heterostructure to prevent indium desorption from the QDs. A change in the indium content in the seed-layer InAs QDs changes the self-assembly position and modifies the In x Ga1–x As layer thickness. A theoretical approach was presented to study the formation of self-assembled In x Ga1–x As layers at each strain-free layer. We showed that the strain energy at the second intermediate (ε zz2) layer is greater than that at the first intermediate (ε zz1) layer; ε zz2 depends on the vertical strain channel length. The impact of the In x Ga1–x As layer thickness on the strain energy was studied using high-resolution transmission electron microscopy; a shorter strain channel length was found to facilitate the formation of a more relaxed and larger-sized self-assembled In x Ga1–x As layer in the active layer. This In x Ga1–x As layer formed at the intermediate layer acts as a capping layer or a protective shield for the indium adatoms, preventing their desorption from the InAs QDs. Furthermore, we studied the thermal stability of the self-assembled In x Ga1–x As layer by annealing the VCBQD samples at 700 and 800 °C. This aspect has been investigated for the first time ever in a study of the coupling efficiency between the InAs QDs and In x Ga1–x As capping layer. A high-resolution in-plane (2θχ/ϕ) reciprocal space mapping (RSM) technique provided the connection between the in-plane reciprocal lattice point of the InAs QDs and In x Ga1–x As layers and revealed the strain and coupling between them. InAs QDs fully covered with the self-assembled In x Ga1–x As layer enhanced the photoluminescence intensity by 77% and had an activation energy of 467 meV.

In-situ tailoring of band alignment between strain-coupled surface and buried InAs/GaAs quantum dots for sensor applications

“…The peak at 66.05°with the maximum intensity corresponds to the peak of the substrate (GaAs). 23 The following formula has been used to compute the average compressive strain: 24,25…”

Quantum Dots and Their Applications: What Lies Ahead?

“…To address this problem, vertically coupled QD bilayers with large enhancement in the PL intensity were achieved by capping the QDs by self-assembled In x Ga 1−x As layers. 5 Another problem usually found in epitaxial QD systems is postprocessing analysis. A new approach to solving this issue has been demonstrated using chemically etched semiconductor nanomembranes and scanning tunneling spectroscopy.…”

“…However, the high temperature of the growth process can introduce problems to interface control, due to In desorption, for example. To address this problem, vertically coupled QD bilayers with large enhancement in the PL intensity were achieved by capping the QDs by self-assembled In x Ga 1– x As layers . Another problem usually found in epitaxial QD systems is postprocessing analysis.…”

Exploring the Implementation of GaAsBi Alloys as Strain-Reducing Layers in InAs/GaAs Quantum Dots

“…The first SRL material used for InAs QD lasers was InGaAs [ 10 , 11 ], but other SRL materials have also been explored, such as InAlAs [ 12 ], GaAsSb [ 13 , 14 ], and quaternary compounds such as InGaAsN [ 15 , 16 ], InGaAsSb [ 17 ], GaAsSbN [ 18 , 19 ], or GaAsSb/GaAsN superlattices [ 20 ]. These SRLs can offer more flexibility in band structure design and other advantages such as avoiding In segregation [ 21 ], increasing the energy separation between the ground and excited states [ 22 ], suppressing QD decomposition [ 23 ], forming type-II band structures [ 24 , 25 ], and overall, extending the emission wavelength [ 7 , 9 ].…”