In situ laser light scattering studies on the influence of kinetics on surface morphology during growth of In0.2Ga0.8As/GaAs

Abstract

Using real-time in situ laser light scattering we study, in this work, the influence of growth kinetics on the initial development of the crosshatched morphology and its subsequent evolution. The crosshatched morphology is characteristic of relaxed low strained layers ͑Ͻ 2%͒ and has been traditionally related to the plastic relaxation process driven by generation and multiplication of dislocations. However we have observed that, if the growth rate is slow enough, the onset of crosshatch formation takes place at a layer thickness in which the dislocation formation and multiplication processes have not appeared yet. This reveals that the stress field generated by the small density of misfit dislocations formed by bending of the dislocations preexisting in the substrate is strong enough to affect the evolution of the growth front morphology. Our results also show that the starting point and evolution of this characteristic morphology depend on the growth rate in such a way that when the growth rate is lower the crosshatched morphology starts to develop at a smaller thickness and shows a faster evolution rate.

In situ detection of an initial elastic relaxation stage during growth of In0.2Ga0.8As on GaAs(0 0 1)

“…When the plastic relaxation stage is reached, the ex situ XRD relaxation values are again in agreement with the in situ results (see Table 1 for around 400-nm-thick layers), and the morphology develops a characteristic crosshatched pattern [5]. Figure 2 shows an AFM image of the 50-nm-thick sample grown at 0.2 ML/s.…”

“…We employ lock-in detection in order to reject spurious signals coming from the hot effusion cells and to improve the signal-to-noise ratio [5,12]. The ex situ surface morphology characterization has been carried out by atomic force microscopy (AFM).…”

“…In a previous work [5], we associated the increase in scattered light to the development of these high ridges built on top of the misfit dislocations formed by the Matthews mechanism. However, our present in situ stress results show an elastic relaxation stage taking place during the growth, which cannot be accounted for by the low density of ridges formed at the surface.…”

“…In a previous work we studied the influence of kinetics on the morphological evolution during growth of In 0.2 Ga 0.8 As/GaAs by molecular beam epitaxy (MBE) using in situ laser light scattering (LLS) [5]. We found that surface roughening takes place before the dislocation multiplication processes begin to actuate.…”

“…As the growth proceeds, an increasing amount of accumulated elastic energy makes the layer to become metastable and the relaxation process begins [1,2]. Relaxation of low-strained layers ( < 2 %) usually takes place through misfit dislocations, and it is well known that the surface of these layers develops an undesired crosshatched morphology once the mechanisms for plastic relaxation start [3][4][5]. Furthermore, some studies on the low-mismatched SiGe/Si [6,7] and In x Ga 1-x As/InP (x  0.53) [8] systems have shown that the surface can also roughen prior to the generation of misfit dislocations and the subsequent crosshatch development.…”