Optical emission from InAs/InP self-assembled quantum dots: evidence for As/P intermixing

Abstract

We have studied the optical properties of ultrathin InAs/InP quantum wells and Stranski-Krastanov nanostructures using photoluminescence and photoluminescence excitation experiments. For InAs epilayers thinner than 2.4 monolayers, the emission spectrum consists of a single peak and the ground-state exciton energy is in good agreement with predictions based on the tight-binding method for ultrathin quantum wells. Beyond this thickness, the photoluminescence spectra evolve to a multimodal emission indicative of the presence of families of quantum dots with small heights. The emission of these quantum dots is blue-shifted significantly (∼100 meV) from the predicted values. The discrepancy is explained by As/P intermixing that occurs during quantum dot formation.

Temperature dependence of the photoluminescence spectra from InAs(P)/InP multilayers containing thick quantum dots: Dot-size-dependent carrier dynamics

“…This is coherent with the distribution of diameters observed in the TEM plane view. Intermixing between As and P is expected to occur during the growth of such samples; the composition that we have deduced agrees well with those found for much thinner InAs layers deposited with the same system (x = 12% using k.P theory) 9 and for QD's grown by chemical beam epitaxy (x = 6%-10% based on tight-binding calculations). 11 The white curves in Fig.…”

“…Indeed, since the lateral confinement energy in these low-aspect-ratio InAs/InP QD structures is small, 7 we can reasonably describe their emission energies using those for quantum wells (QW's) with the same number of monolayers (ML's). 9,11,29 The excited states due to the lateral confinement, since they lie only a few meV above the ground state, should cause a widening of the emission peaks of each family (associated with a ground state and eventually excited states arising from vertical confinement), as does the lateral size distribution of dots of the same height, in addition to a slight blueshift.…”

“…In fact, SK-grown InAs nano-islands embedded in InP(001) have shown optical emission spectra covering a wide photonenergy range, depending on the quantity of material deposited and on the duration of the growth interruption time during which island formation takes place. [7][8][9][10][11] Indeed, one can observe emission from well-defined peaks, each associated to a family of thin dots of the same heights, in the 0.8-1.1 eV energy range, 9,11 while emission from thicker dots in the 0.6-0.8 eV region rather results in broader peaks 8,10 with an indiscernible contribution from the different families, since the energy separation between two successive families decreases as the thickness of the dots is increased. In the latter case, the carriers are deeply confined, so a more stable emission behavior with temperature can be expected from such nanostructures, as compared with InAs/GaAs or thinner InAs/InP QD's.…”

Carrier thermal escape in families of InAs/InP self-assembled quantum dots

“…The PLE spectra of peaks A1 and A2 are similar to what was previously reported in thin InAs QWs. 27,30 They show an edge at 1.19Ϯ 0.01 eV and a resonance at 1.31Ϯ 0.01 eV that correspond, respectively, to the electron to heavy-and light-hole transitions in a 2-ML-thick InAs/InP QW as calculated with the tight-binding method. 27,31 It follows that the high-energy tail of the emission from sample A at low temperature corresponds to residual emission from the WL.…”

“…In order to solve some of the problems mentioned above, we present a study of the thermal quenching from two samples that contain a single layer of InAs QDs embedded in an InP matrix. Their PL spectra show several well-resolved emission bands, extending from 0.75 to 1.1 eV, that can be associated with families of QDs that differ in height by 1 ML, [21][22][23][24][25][26][27][28] while their PL excitation ͑PLE͒ spectra reveal absorption edges that we associate with QD excited states and WL resonances. The evolution with temperature of the multimodal PL of our samples imposes stringent constraints on a model based on coupled rate equations as it should reproduce the thermal behavior of many peaks with the same set of parameters.…”