Excitation transfer in stacked quantum dot chains

Abstract

Stacked InAs quantum dot chains (QDCs) on InGaAs/GaAs cross-hatch pattern (CHP) templates yield a rich emission spectrum with an unusual carrier transfer characteristic compared to conventional quantum dot (QD) stacks. The photoluminescent spectra of the controlled, single QDC layer comprise multiple peaks from the orthogonal QDCs, the free-standing QDs, the CHP, the wetting layers and the GaAs substrate. When the QDC layers are stacked, employing a 10 nm GaAs spacer between adjacent QDC layers, the PL spectra are dominated by the top-most stack, indicating that the QDC layers are nominally uncoupled. Under high excitation power densities when the high-energy peaks of the top stack are saturated, however, low-energy PL peaks from the bottom stacks emerge as a result of carrier transfers across the GaAs spacers. These unique PL signatures contrast with the state-filling effects in conventional, coupled QD stacks and serve as a means to quickly assess the presence of electronic coupling in stacks of dissimilar-sized nanostructures.

GaAsPBi epitaxial layer grown by molecular beam epitaxy

“…These in-plane compositional different areas are partly, if not completely, the physical origins of the multiple luminescent peaks observed by PL (figure 6). Indeed, the multiple peak luminescence of quantum dot chains grown on cross-hatch patterns was previously reported for InGaAs system [33], this related structure yet different material system should have similar behaviors. For the first series, the luminescence shifts to lower energies with increasing BEP Bi as seen in the lower three spectra in figure 6.…”

“…Luminescence of GaAsPBi generally comprises multiple peaks as shown in figure 6. One of the peaks associated with GaAs substrate (blue fitted curves) is centered at 1.49-1.50 eV [33]. Some of the peaks deviated from the bulk band gap of GaAs (1.51 eV at 20 K) are associated with either the strain from the overgrown layer or the carbon contamination.…”

Ultrathin epitaxial InAs layer relaxation on cross-hatch stress fields

“…The CHP peak indicates that the presence of the underlying dislocations does not severely impact the optical quality of the overlying layers, in good agreement with previous studies. 35,36 In addition, though the surface layer is not optimized in terms of luminescence efficiency, it is evident from the spectra that the ultrathin InAs layer is the most optically efficient. Its peak position at 1.45 eV agrees well with that of a previous report.…”