CHARACTERIZATION OF MOVPE-GROWN (AL,IN,GA)N HETEROSTRUCTURES BY QUANTITATIVE ANALYTICAL ELECTRON-MICROSCOPY

The low pressure metalorganic vapor phase epitaxy growth of wurzite (A l, In, Ga)N heterostructures on sapphire substrates is investigated by quantitative analytical scanning transmission electron microscopy tec hniques like atomic number (Z-) contrast imaging and convergent beam e lectron diffraction (CBED). Especially (In, Ca)N quantum wells of diff erent thicknesses as well as superlattices were analyzed with respect to defects, chemical composition variations, interface abruptness and strain (relaxation) effects. The interfaces in In0.12Ga0.88N/GaN quant um wells appear to be asymmetric. Additionally, we found composition v ariations of Delta x(In) greater than or equal to 0.03 within the InGa N quantum wells. The application of electron diffraction techniques (C BED) yields quantitative information on strain and relaxation effects. For the case of 17 nm thick InGaN quantum wells, we observed relaxati on effects which are not present in the investigated thin quantum well s of 2 nm thickness. The experimentally obtained diffraction patterns were compared to simulations in order to get values for strain within the quantum wells. Additionally, the influence of dislocations on the digression of superlattices is investigated.