MOCVD Growth And Characterizations Of InAs/GaAs Self-Assembled Quantum Dot Heterostructures

Due to the three-dimensional carriers confinement, the energy level of quantum dot (QD) heterostructures is discrete and the density of states represents a set of delta-function peaks at the atomic-like energy levels. Therefore, the photoelectric property of QD heterostructures is significantly improved which is beneficial to the development of new optoelectronic devices. In particular, QD lasers is easy to achieve the longer emission wavelength and has higher temperature stability compared with conventional quantum well lasers. In the past decade, QDs have become one of focus of study in the field of nano-semiconductor science.Currently, the research level of InAs QDs and devices based on QDs grown by molecular beam epitaxy (MBE) is close to the practical level. However, the growth of InAs QDs by Metal Organic Chemical Vapor Deposition (MOCVD) is still challenging due to more complexity and less controllability of QDs growth process in MOCVD system.The thesis is focused on the study of controllable technology of InAs/GaAs QDs grown by MOCVD. The mainly research work is listed as follow:1. The effect of growth parameters on InAs QDs during the growth process using MOCVD was studied. The higher growth temperature results in the lower density, the larger size and the longer emission wavelength. The lower growth rate leads the wavelength redshift. The higherⅤ/Ⅲleads to a faster process of nucleation and islands ripening, so the density is reduced. The growth interrupt is necessary for the formation of InAs QDs. During this process, a higher AsH3 flow typically results in fast island ripening and increment of island size. Higher InAs coverage enhances InAs QDs density. At InAs coverage of 2.5ML, density reached 1.5×1011cm-2. But if the coverage continues to increase, density begins to decrease due to the appearance of larger islands.2. With the cooperation of other researchers, when In0.15Ga0.85As was used as overgrown layer and InAs coverage was 3.6ML, the emission wavelength of InAs QDs at room temperature reached 1328nm, and the full-width at half-maximum (FWHM) value was 44meV.530℃, 0.06ML/s were chosen as growth temperature and growth rate, respectively. TheⅤ/Ⅲwas 10.3. For 2-layers InAs/GaAs QDs, lower growth rate made density of InAs QDs approached the density of previous layer. The uniformity was enhanced and the variance of height was down to 0.5nm. Three layers InAs/GaAs QDs sample were achieved with wavelength of 1169nm and FWHM of 107meV.4. The influence of incorporating boron into InAs/GaAs QDs was studied. When B0.05Ga0.95As of 10 nm thickness was incorporated into GaAs buffer layer, the strain field of the growth surface became more uniform and stable. At InAs coverage of 3ML, density of InAs clusters was significantly decreased. On the other hand, for the BInAs/GaAs QDs, the critical thickness is significantly increased as the boron composition of QDs became higher. When the boron incorporated 40 sccm, no QDs were observed.