Growth and excitonic properties of single fractional monolayer CdSe/ZnSe structures

Abstract

Single fractional monolayer (FM) CdSe/ZnSe structures have been grown by molecular beam epitaxy (MBE), employing both conventional MBE and migration-enhanced epitaxy (MEE). A precise calibration of the FM mean thickness in the range of 0.15–3.0 ML has been performed for both techniques, revealing more than a 3.5 times lower Cd incorporation ability for the MEE mode at the same Cd and Se incident fluxes. Steady-state and time-resolved photoluminescence spectroscopy is used to characterize the intrinsic morphology of the CdSe FMs, with a special emphasis on the submonolayer thickness range. Both MBE and MEE grown samples exhibit inhomogeneity of the excitonic system, which can be explained by coexistence of a homogeneous alloylike layer and relatively large CdSe 2D clusters. The MEE samples display smaller fluctuations of the layer thickness and island sizes.

Optically Pumped Low Threshold ZnSe Based Lasers with 2.8 ML CdSe Active Region

“…Figure 2 presents the low-temperature PL and PLE spectra of the FM structure and of the reference QW structure. The CdSe FM PL band is much broader ( 80 meV) and inhomogeneous, and most probably involves two peaks as have been reported in [6]. Contrary to the spectra of the QW structure, the PLE spectra of the FM structure depend on the registration energy marked by arrows in Fig.…”

“…Laser structures with CdSe FM active region consist of 20 nm ZnSe buffer layer, a 0.5 m thick ZnMgSSe bottom cladding layer, a 28-period (3 nm ZnS0.14Se0.86/5 nm ZnSe) SL waveguide surrounding a 10 nm wide ZnSe QW centered with a 2.8 ML CdSe FM, and, finally, a 0.1 m ZnMgSSe top cladding layer protected by a 5 nm ZnSe cap. Both conventional MBE and migration-enchanced epitaxy (MEE) techniques [6,7] were used for the CdSe FM growth. The reference structures with the similar design contain the conventional 7-10 nm (Zn,Cd)Se QW with the same as in the SL well Cd content varied from 0.27 to 0 (pure ZnSe).…”

CdSe Layers of Below Critical Thickness in ZnSe Matrix: Intrinsic Morphology and Defect Formation

“…By varying the molecular beam epitaxil (MBE) growth conditions and thickness of thin CdSe layer on a ZnSe surface, three different regimes have been reported: (i) Stranski-Krastanov (SK) island growth mode (above tcr) [4][5][6], including thermal activation regime [7], (ii) pseudomorphic growth of thin CdSe or ZnCdSe quantum-well-like (QW-like) layers (below t^,.) [8][9][10], and (iii) coexistence of extended islands and the alloy-like phase (w < 1 ML) [11][12][13]. The SK growth mode was found to produce the dot-like CdSe-based islands with lateral sizes far beyond 10 nm, which cannot provide sufficient 3D confinement.…”

“…In contrast to the MBE growth mode, FM structures grown in the ΜΕΕ mode demonstrate a more than threefold reduced CdSe growth rate. The details of the CdSe FM growth by MBE and ΜΕΕ have been reported elsewhere [11]. The PL measurements were performed at low (1.8 K) temperature using the 351 nm line from a cw Ar+ laser.…”

“…Zhu et al [8] have interpreted this fact for sub-monolayer w region by the formation of uniform ZnCdSe alloy layer at the CdSe/ZnSe interface. The recent investigations have revealed the complicated structure of fractional monolayers (FMs) involving both the alloy-like homogeneous layer, which can probably be formed by small, with respect to rB, islands, and extended 2D ones [11][12][13].…”