InAs quantum dot morphology after capping with In, N, Sb alloyed thin films

Abstract

Using a thin capping layer to engineer the structural and optical properties of InAs/GaAs quantum dots (QDs) has become common practice in the last decade. Traditionally, the main parameter considered has been the strain in the QD/capping layer system. With the advent of more exotic alloys, it has become clear that other mechanisms significantly alter the QD size and shape as well. Larger bond strengths, surfactants, and phase separation are known to act on QD properties but are far from being fully understood. In this study, we investigate at the atomic scale the influence of these effects on the morphology of capped QDs with cross-sectional scanning tunneling microscopy. A broad range of capping materials (InGaAs, GaAsSb, GaAsN, InGaAsN, and GaAsSbN) are compared. The QD morphology is related to photoluminescence characteristics.

Variation of the photoluminescence spectrum of InAs/GaAs heterostructures grown by ion-beam deposition

“…The solution to the problem can be found by the selection of a potential-barrier material for QDs based on III–V multicomponent solid solutions. GaAsSb [26], InGaAs [27], InGaAsN [28–29] and GaAsNSb [30–31] have been used for these purposes. In this work, it is proposed to use GaAsBi.…”

Tuning the properties of InAs/GaAs quantum dots through a modified capping layer: Application to optoelectronic devices

“…Such a process seems to impose a generalized evolution towards the thermodynamic equilibrium during overgrowth whereby QDs are similarly levelled, regardless of the initial QD size. (when available) and after the capping process (red and blue dots, respectively) [73,[108][109][110][111][112][113][114]. A schematic of the QD dissolution process during capping is also represented in the inset, whereby the QD top flattens through surface In-Ga intermixing and surface diffusion of In leads to the WL thickening (orange layer).…”

“…U l lo a e t a l . [109,113,[115][116][117]. On the other hand, this approach additionally allows tailoring the electronic structure of the QDs and the emission wavelengths of InAs QDs have been extended to the 1.3-1.55 µm region using InGaAs [40,[118][119][120] and GaAsSb [41,42,106,121] strainreducing CLs.…”

“…It has been demonstrated that the strain field surrounding the QD is not the only parameter affecting the dissolution of QDs. The use of GaAsN strain-compensating CLs 2 is of particular interest, since the QD erosion during the overgrowth is reduced despite the larger lattice mismatch between the QD and the GaAsN CL [109]. Stronger Ga-N bonds as compared to those of Ga-As are believed to reduce intermixing and surface diffusion during capping, increasing the final QD height.…”

“…Moreover, the incorporation of N in GaAs, according to the band-anticrossing (BAC) model [122], reduces the band gap through only lowering the conduction band of GaAs. This allows extending the emission of InAs QDs towards the telecommunication wavelengths [110,123], while switching the band alignment to a type II structure for relatively low N contents [109]. Moreover, N-containing CLs act as straincompensating layers, which is critical to avoid defect formation due to accumulated strain in multi-QD-layer stacks [124].…”