Electronic and Optical Properties of InAs QDs Grown by MBE on InGaAs Metamorphic Buffer

Abstract

We present the optical characterization of GaAs-based InAs quantum dots (QDs) grown by molecular beam epitaxy on a digitally alloyed InGaAs metamorphic buffer layer (MBL) with gradual composition ensuring a redshift of the QD emission up to the second telecom window. Based on the photoluminescence (PL) measurements and numerical calculations, we analyzed the factors influencing the energies of optical transitions in QDs, among which the QD height seems to be dominating. In addition, polarization anisotropy of the QD emission was observed, which is a fingerprint of significant valence states mixing enhanced by the QD confinement potential asymmetry, driven by the decreased strain with increasing In content in the MBL. The barrier-related transitions were probed by photoreflectance, which combined with photoluminescence data and the PL temperature dependence, allowed for the determination of the carrier activation energies and the main channels of carrier loss, identified as the carrier escape to the MBL barrier. Eventually, the zero-dimensional character of the emission was confirmed by detecting the photoluminescence from single QDs with identified features of the confined neutral exciton and biexciton complexes via the excitation power and polarization dependences.

Structural properties of graded In x Ga 1−x As metamorphic buffer layers for quantum dots emitting in the telecom bands

“…In particular, the average height increases by 0.5 nm by decreasing the growth temperature from 420 • C to 410 • C, leading to weaker confinement in the growth direction and thus longer emission wavelength. Indeed, in addition to the mismatch between matrix and QDs on such MBL structures, the height of the QDs has been identified as an important factor for determining the final emission wavelength, as indicated by simulations [15]. As presented in figure 4(d), we notice that the size distribution of the QDs grown at 410 • C is larger than the one grown at 420 • C. This is consistent with the increase of the FWHM from a value of 45 nm to 67 nm with decreasing QD growth temperature.…”

“…The spectrum consists of several emission lines, whereby the marked peaks can be identified as exciton (X) and biexciton (XX) separated by a binding energy of 2 meV, as well as the negative trion (X − ) showing a binding energy of 1.7 meV. These values are similar to the ones reported in literature for QDs grown on top of a graded MBL [15] and for QD emitting in the same wavelength range due to capping with a InGaAs strain-reducing layer [38,39]. For a detailed assignment of the other emission lines, more dedicated experiments are required, which are out of the scope of the current work.…”

“…Importantly, it has also been proven that such systems can be used for the generation of entangled photon pairs [13]. The MBE growth of linearly graded MBLs combined with the digital alloying approach was also recently achieved and enabled single-photon emission in the C-band [14,15].…”

Annealing-Modulated Surface Reconstruction for Self-Assembly of High-Density Uniform InAs/GaAs Quantum Dots on Large Wafers Substrate

“…Self-assembled InAs quantum dots (QDs) have been used in optoelectronic devices, such as laser diodes [ 1 ], super-luminescence diodes [ 2 ], quantum emitters [ 3 ] and photodetectors [ 4 ], with flexible wavelength tuning by metamorphic growth [ 5 , 6 , 7 ], compatibility with silicon for integration [ 1 , 8 , 9 ], high working temperatures (T) [ 10 ] and speed [ 11 ]. Molecular beam epitaxy with simple nucleation mechanism, ultra-high vacuum and precise shutter could fabricate defect-free QDs with exciton formed [ 12 ].…”