EPITAXIAL LAYERS VERSUS BULK SINGLE CRYSTALS OF GaN. TEMPERATURE STUDIES OF LATTICE PARAMETERS AND ENERGY GAP

摘要

Gallium nitride epitaxial layer grown by molecular beam epitaxy and bulk crystal grown at high pressure were examined by using X-ray diffraction methods, and by optical absorption at a wide temperature range. The free electron concentration was 6 x 10~(17) cm~(-3) for the layer and about 5 x 10~(19) cm~(-3) for the bulk crystal. The experiments revealed a different position of the absorption edge and its temperature dependence for these two kinds of samples. The structural examinations proved a significantly higher crystallographic quality of the bulk sample. However, the lattice constants of the samples were nearly the same. This indicated that a rather different electron concentration was responsible for the different optical properties via Burstein-Moss effect.