Effects of growth temperature of partial GaAs cap on InAs quantum dots in In‐flush process for single dot spectroscopy

Abstract

We have investigated effects of growth temperature of partial GaAs cap (Tcap) on InAs quantum dots (QDs) in indium‐flush (In‐flush) process with atomic force microscopy (AFM) and micro photoluminescence (μ‐PL) measurements. Tcap in In‐flush process are varied from 385 °C to 485 °C as an experimental parameter. In order to investigate the effects of Tcap on structural property of single InAs QD, shape of QD in initial capping process are characterized by AFM measurements in air at room temperature. While isotropic shape of QDs is kept in low Tcap conditions below about 440 °C, in‐plane anisotropy of initial shape of QDs are increased with increasing of Tcap due to elongation to the [1$ \bar 1 $0] direction. μ‐PL measurements are performed at 7K for the investigation of the effects of Tcap on optical property in single InAs QDs. In low Tcap conditions from 410 °C to 435 °C, distinct emissions from excitonic states in single QDs are observed. In the same Tcap range, the AFM result shows that isotropic shape of QDs is kept. On the other hand, in high Tcap conditions above about 440 °C, indefinite peaks and broad emissions appear remarkably. Excitonic emissions which are observed in low Tcap range are hardly observed in this high Tcap range (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Improved optical properties of low density InAs/GaAs quantum dots by controlling partial capping process

“…We observed the degradation of a QD emission quality when using Tp.cap of above 465 °C for QDs grown with a slightly different growth condition (not shown). This is probably because the excess annealing weakened the quantum confinement effect in the QDs by strong intermixing between the QDs and barriers as well as by the erosion of the QD shape [2]. Thus, we consider that Tp.cap of 465 °C is the optimum value for obtaining low density and narrow emissions.…”

“…Especially when utilizing the quantum nature of single QDs, the growth of low density QDs with distinct narrow-linewidth emission is primarily required. In addition, the reduction of a broad background emission is desirable in order to reduce the unwanted optical absorption in the photonic nanostructures [2]. An emission wavelength of around 940 nm is also required for using highly sensitive Si photodetector and avoiding absorption from InAs wetting layer (~900 nm).…”

“…Gong et al reported that the higher capping temperature induced more segregation of In atoms from the QDs and caused a large Ga-In intermixing [3]. The growth temperature of the partial capping layer also affected the optical quality of the QD emissions [2]. Costantini et al reported the intermixing was almost independent of the growth rate of the partial capping layer [4].…”

PL of low‐density InAs/GaAs quantum dots with different bimodal populations

“…We then raised the substrate temperature to 600°C and annealed the samples for 8 min. This partial capping growth and the following annealing have been proved to effectively modify the dimensions, uniformity, and quality of the InAs QDs [12, 13, 19, 20]. After annealing, the sample was capped with an additional 250 ML of GaAs at 600°C.…”

Design and Realization of Novel GaAs Based Laser Concepts

“…Figure 4.5). Capping of the QD layer with GaAs before increasing temperature again is essential for preventing indium flushing at higher temperatures [Sas07,Kum11]. As this capping layer is grown at the same low temperature as the QDs themselves, it exhibits inferior material quality which likely contains a higher density of point defects than GaAs fabricated at the optimum temperature.…”