Study On Controllable Growth Of InGaAs Quantum Dots

The electronic devices, microwave devices and integrated circuits produced by III-V compound semiconductors show high speed and high frequency performances,due to the high electron mobility of III-V compound materials. In addition, low dimensional materials such as quantum well, quantum wire and quantum dot made from III-V compound semiconductors have excellent optical characteristics, which is important to high photoelectric conversion rate of photovoltaic module, low threshold current of high power semiconductor lasers and high sensitivity infrared detectors and so on. These devices are widely applied in military technology, space technology, and daily life because of its superior performance. In order to developing the photovoltaic performance of III-V semiconductor devices now, people pay more attention to the study on low dimensional semiconductor devices, especially, those devices made from three-dimensional limited quantum dots. The high quality of III-V semiconductor quantum dots is the key to ensure optical and electrical properties of quantum dots and their range of applications. In this paper, the study shows that the growth of single-layer or multi-layer quantum dot can be controlled for the material system of InGaAs / GaAs, the purpose of this study is to obtain a highly uniform and efficient quantum dot material. The main contents of this paper are the following:1. Based on the research of GaAs and In As homoepitaxy, the atomically flat GaAs(001)surface has been obtained and the composition of InGaAs quantum dots has been determined. And then, the relationship for quantum dots growth with quantum dots composition and substrate temperature has been researched. The results showed that the specific composition and substrate temperature are necessary to 3D quantum dot formation in Stranski-Krastanov mode. With the specific composition,there is a suitable temperature range for quantum dots growth, only within that range can form quantum dots. The temperature range for growth of quantum dots will expand with the increase of indium composition. When the indium composition was low(indium composition less than 20%), it was unable to generate quantum dots effectively.2. The size and density of quantum dots determined optoelectronic properties and application range of quantum dot materials. By adjusting growth mode, the amount of deposited materials and annealing condition, the size and density of the monolayer quantum dots in the two-dimensional surface can be effectively controlled. Studies have shown that in appropriate temperature range, the higher temperature will make larger quantum dots; and the annealing process can greatly improve the quantum dots height and lateral dimension, at the same time, lower their density. However, if the growth temperature is too low, the density of quantum dots will not decrease after annealing, it will increase slightly instead. SK growth mode is found to be suitable for grow high-density quantum dots while droplet epitaxy for low-density quantum dots.The amount of deposited metal and the annealing time without arsenic pressure are key factors to determine quantum dots shape, size and density. In the improved deposition process, Indium and gallium materials that injected to substrate surface intermittently can effectively control the density of quantum dots. In the gallium droplet epitaxy, nano-holes can act as templates for quantum dots prior nucleate.3. Based on the single-layer quantum dots growth technique, we studied the growth process of multi-stacked quantum dots. There exists two spatial distribution mechanisms in multi-stacked quantum dots, which are vertical and lateral alignment respectively, and both of these two mechanisms were affected by the spacer layers thickness. The spacer layer which plays as a transfer media for stress influences the spatial distribution of multi-stacked quantum dots. When the spacer layer is thin, the quantum dots will align vertically, while the quantum dots will align laterally when the spacer layer is thick. In addition, the thickness of the spacer layer, the growth technique and the annealing process for the spacer layer will directly influence the quantum dots size, shape and density. Therefore, the properties of multi-stacked quantum dots can be effectively controlled by adjusting the growth process of spacer layer。4. For the self-assembled quantum dots, stress and strain distribution will directly influence quantum dots energy band. In this paper, we characterized the single-layer quantum dots surface micro-structure under different annealing time, the resultsindicated that the release of internal strain energy will result in cracks in the quantum dots, and the external stress will make quantum dots shapes change. In addition, the high-resolution STM was utilized to characterize the quantum dots surface micro-structure; we first discovered that the side facet of In0.5Ga0.5As quantum dots is InAs(137) facet. By analyzing the influence of spacer layers surface strain to the multi-stacked vertical and lateral alignment quantum dots, we found that the vertical alignment of quantum dots is only related to surface strain, however, the quantum dots distributed in lateral alignment is the result of surface topography and surface strain acting together.