Optical emission and its decay time of type-II InP/GaAs quantum dots

Abstract

We investigated the optical emission at 2 K from InP quantum dots (QDs) grown on GaAs with and without a GaAs capping layer. Uncapped QDs present relatively long emission decay times (4–14 ns). In contrast, dots covered with a GaAs layer present much shorter lifetimes (∼1 ns). We analyse those results considering the effects of surface states (non-radiative recombination channel) and intermixing at the interfaces (affecting the electron–hole wave-function overlap). The continuous-wave optical emission spectrum from uncapped dots does not reproduce straightforwardly the dot size distributions obtained by atomic force microscopy measurements, showing an enhancement of the emission from small dots. The result is attributed to the strong dependence of the electron–hole wave-function overlap with the dot size obtained by our calculations.

Spatial carrier distribution in InP/GaAs type II quantum dots and quantum posts

“…Since our structures are not covered with a GaAs layer, surface states at the InP top layer may contribute as an efficient non-radiative channel (small τ NR ) as compared to capped single QD structures. Furthermore, uncapped single layer InP/GaAs QD structures [9], which should have similar density of nonradiative centers to our stacked QDs, present longer PL decay times (∼5-12 ns) than those obtained in capped single layer QDs [8]. The short lifetime obtained for the latter was attributed to interface intermixing effects and it indicates that the top InP/GaAs interface should present a more significant intermixing than the bottom GaAs/InP interface of the QD.…”

“…In a recent work, rather short photoluminescence (PL) decay times have been observed for single and double layer InP/GaAs QDs [8], which are attributed to interface intermixing effects that result in an increase of the e-h wavefunction overlap and, therefore, a decreasing of the PL decay time. However, long decay times were observed in uncapped InP/GaAs QDs [9] where intermixing effects from the QD top interface are less important, corroborating that improvement of the interface quality is essential to use this system for bandgap engineering applications.…”

“…The emission related to the QDs structures consists of two bands, labeled A and B. In previous works on single layer InP/GaAs QD structures, the WL emission was observed at ∼1.41-1.45 eV [12,17], while the QD emission band energy varied between 1.38 and 1.40 eV [3,8,9,18]. The band A from sample S3, for which we expect a negligible coupling between vertically separated WLs, is within the energy range for the previously observed WL emission [12,17].…”

Nucleation and growth evolution of InP dots on InGaP/GaAs

“…Although structural information is usually obtained from microscopy data, an important and complementary tool for III-V materials is the photoluminescence (PL) technique. The electronic structure analysed by PL can be used as a probe to detect changes both in the WL and the QD shapes, as well as the effect of surface processes and interface fluctuations on these characteristics [13,14]. Recently, both macroand micro-PL techniques have shown improved confinement energies and luminescence intensities for InP QDs using (f ) 4.0 Eq-ML.…”

Efeito de interface nas propriedades ópticas de pontos quânticos de InP/GaAs

“…Enquanto alguns resultados experimentais mostram evidências do comportamento de alinhamento de bandas do tipo II, como o desvio do pico do espectro de fotoluminescência para o azul com o aumento a intensidade de excitação [10], foi observado que o decaimento temporal da emissão óptica é relativamente curto (~1ns ou menores) [10,11,12], similar a um sistema do tipo I. Entretanto, medidas de fotoluminescência em pontos quânticos superficiais, sem a cobertura de camada de GaAs, resultam em tempos de decaimento longo (~10ns) [13,14], indicando uma separação espacial entre elétron e buraco. Esses resultados geraram a suspeita que a interface entre InP e GaAs não é abrupta, ocorrendo mistura de átomos nas interfaces.…”