Structural and optical properties of shape-engineered InAs quantum dots

Abstract

Shape-engineered InAs quantum dots (QDs) were grown by using thin In0.15Ga0.85As and a monolayer (ML) of InAs with different periods on 3 ML InAs QDs and their structural and optical properties were investigated by transmission electron microscopy (TEM), photoluminescence (PL), and photoreflectance (PR) spectroscopy. Cross-sectional TEM images of the QD samples showed that the shape, particularly the height of the QD, could be effectively controlled without any significant degradation in QD quality, such as the generation of dislocations in the QD, thus changing the optical properties. PL and PR spectra indicated that all the layers required for the formation of shaped-engineered QD were grown without any degradation in QD properties. PL spectra of shape-engineered QDs that had been subjected to rapid thermal annealing showed an abnormal behavior compared to those of conventionally grown InAs QDs.

Optical characterisation of MOVPE grown vertically correlated InAs/GaAs quantum dots

“…The most popular technique, photoluminescence (PL), works best at low temperatures and yields mainly ground-state interband transitions. On the other hand, photomodulated reflectance (PR) spectroscopy [5], which is rarely used experimental method for checking of QD structures [6], uses laser pump source to periodically perturb sample dielectric function. The alternating component of the sample reflectance, which is subsequently measured, exhibits sharp derivative-like spectral features in the region of interband transitions.…”

Shape-dependent optical properties of self-assembled InAs/GaAs quantum dots

“…The difference in the bias-dependent optical properties between two QD samples can be largely related to the internal electric field mainly caused by the effective shape of InAs QDs. In the previous works, since the low symmetry QD ensembles can significantly reduce the overlap of the electron and hole wave functions, a highly symmetrical QD such as hemispherical or cylindrical shape is believed to have better QD properties [6,7]. In the present work, under the assumption that the effects of the external bias voltage on the optical properties are same, the internal electric field caused by the QD shape for the QD1 sample can be larger than that of the QD2 sample due to its relatively lower symmetry, as shown in Fig.…”

“…As an example, InGaAs and InAlAs layers, so called strain-reducing layers, have been used to control the shape and size of InAs QDs on GaAs, which can modify the optical properties such as the extension of the emission wavelength to 1.3 mm and narrowing the photoluminescence (PL) line width [8,9]. In our previous works, the modification of QDs due to the different growth kinetics of the group III elements, In, and Ga adatoms of the strain-reducing InGaAs layer was demonstrated, resulting in significant changes in the optical properties [7,10]. That is, the emission wavelength was redshifted toward 1.3 mm, and the energy-level spacing between the ground states and the excited states was drastically changed due to the modification of the QD shape and size.…”

“…In order to get the lasing emission from the ground states, the gain of QD lasers should be enhanced by increasing the cavity length, the spatial density in a QD layer and the number of QD layers [6]. Since the maximum modal gain for a QD laser is directly proportional to the overlap integral between the electron and hole wave functions, a highly symmetry QD is also necessary to increase its overlap integral [6,7]. Therefore, the shape of a self-assembled QD should be significantly controlled not only to design the electronic and optical properties but also to improve the device performances.…”

Structural and optical properties of shape-engineered InAs quantum dots in a GaAs matrix emitting at 1.27μm

“…Among the QD fabrication techniques, self-assembled method through the Stranski-Krastanov (S-K) growth mode is one of the most promising ways for the optoelectronic devices such as a laser diode (LD) and a light-emitting diode [2,5]. However, the formation of selfassembled QDs may be quite limited because the 3D quantum structures are naturally evolved via the strain relaxation during the growth of highly lattice-mismatched hetero-epitaxy system such as In(Ga)As/GaAs and In(Ga)As/InP [6,7]. For example, the height of selfassembled QDs is relatively smaller than the lateral size, resulting in the small aspect ratio (height/width, AR).…”