Photoluminescence study of InAs quantum dots embedded in GaNAs strain compensating layer grown by metalorganic-molecular-beam epitaxy

Abstract

Self-assembled InAs quantum dots ͑QDs͒ embedded in GaN 0.007 As 0.993 strain compensating layers have been grown by metalorganic-molecular-beam epitaxy on a GaAs ͑001͒ substrate with a high density of 1ϫ10 11 cm Ϫ2 . The photoluminescence properties have been studied for two periods of InAs quantum dots layers embedded in GaN 0.007 As 0.993 strain compensating layers. Four well-resolved excited-state peaks in the photoluminescence spectra have been observed from these highly packed InAs QDs embedded in the GaN 0.007 As 0.993 strain compensating layers. This indicates that the InAs QDs are uniformly formed and that the excited states in QDs due to the quantum confinement effect are well defined. This is explained by tensile strain in GaNAs layers instead of the usual GaAs layers to relieve the compressive strain formed in InAs QDs to keep the total strain of the system at a minimum.

Improvement of InAs quantum-dot optical properties by strain compensation with GaNAs capping layers

“…E B for the InAs QDs/GaN 0.007 As 0.993 sample is the band gap energy of the GaN 0.007 As 0.993 barrier. 8 The reasonable agreement between the estimated thermal activation energies and the energy differences between the QD state PL subpeaks and the GaNAs barrier shows that the quenching mechanism of the PL intensities is the thermionic emission of carriers from the QD states to the GaNAs barriers, followed by carrier migration in the barrier layers and final nonradiative recombination. In this case, the thermal activation energies are given by the energy difference between the barrier energy and the corresponding QD state transition energies following the Maxwell-Boltzmann statistics of the populated carriers.…”

“…4 The relation of the compressive strain and the luminescence peaks of the InAs QDs has been extensively studied. 5,6 On the other hand, application of tensile-strained GaNAs capping layers to InAs QDs was recently proposed, 7,8 which led to longer wavelength emission up to 1.55 m. The reduction of the compressive strain around InAs QDs with tensilestrained GaNAs capping layers was identified with transmission-electron-microscopy cross-sectional observations. 7,9 The purpose of this paper is to study how optical properties such as luminescence efficiencies and homogeneity of the QDs depend on the selection of the capping layers.…”

“…8. The thermal activation energy of each transition was estimated from the Arrhenius plots of the integrated PL intensities.…”

“…The temperature dependence of the subpeaks in the two samples, of which the peaks were estimated by Gaussian fitting of the observed PL spectra, 8 is shown by the closed circles in Fig. 2.…”

Role of Nitrogen Precursor Supplies on InAs Quantum Dot Surfaces in Their Emission Wavelengths

“…7,8) However this method in principle will accumulate total strain in the system with an increase in the stacked QD layers and this excess strain accumulation can cause degradations of the QD optical qualities. Another approach is to compensate the compressive strain in InAs QDs by burying them with tensile-strained GaAsN layers, 9) and this method demonstrated the systematic extension of the InAs QD emission wavelengths up to ~1.55 µm with an increase in the nitrogen (N) concentrations to 2.7%. 10) This method to bury InAs QDs with the GaAsN strain compensating layer (SCL) has an advantage in that the overall strain is compensated and the accumulation of the total strain in the system can be minimized, which increases luminescence efficiencies up to fivefold compared with QDs buried conventionally with GaAs layers.…”