| The work aims to characterize at atomic scale the interfacial structure and composition of III-V semiconductor quantum heterostructures grown by molecular beam epitaxy (MBE), by using high-resolution transmission electron microscopy (HRTEM) and analytical electron microscopy (AEM). It is shown that the As/P anion exchange can cause many materials problems, such as introduction of misfit dislocations in a dipole configuration, compositional modulation in the GaInP layer, in addition to the well known interfacial composition grading and roughening phenomenon. However, As/P exchange can bring about remarkable improvement in vertical alignment and size uniformity, which are biggest challenges to device growers. The third part of this work is focused on fundamental issues of anion exchange. A thermodynamic model is developed to predict the occurrence of the anion exchange under typical MBE conditions. Both strong-for-weak and weak-for-strong exchanges have been predicted thermodynamically and observed experimentally. Typically, the interfacial layer formed through anion exchange is several atomic layers thick and completely coherent to the substrates. The mechanisms of exchange has been discussed. |
