Transmission electron microscopy and X-ray diffraction studies of quantum wells

A series of InxGa1-xAs (x = 0.47) quantum wells with InP barrier layers have been grown on InP substrates by metalorganic vapour phase epitaxy (MOVPE) at 625 degrees C. The nominal well widths were defined during growth at (i) 25 Angstrom, 39 Angstrom, 78 Angstrom and 150 Angstrom for one sample and (11) 78 Angstrom for all 4 wells in another sample. The InP barrier widths have been kept constant at 150 Angstrom. These layers have been characterized by X-ray diffraction (XRD) which from simulation gave the nominally 78 Angstrom well width as 84 A and the nominally 150 Angstrom barrier width as 150.5 Angstrom. Transmission electron microscopy (TEM) and high resolution TEM (HRTEM) have been carried out on etched and ion-milled samples for direct measurement of well and barrier widths. The well widths found from TEM are 25 Angstrom, 40 Angstrom, 75 Angstrom and 150 Angstrom. TEM micrographs revealed that, while the InP barrier layer is of good quality and the growth is confirmed to be epitaxial, dipoles are detected at the interface and the quantum well has some small disordered regions. These thickness measurements are in good agreement with earlier photoluminescence (PL) and secondary ion mass spectrometry (SIMS) studies.