High Resolution and Analytical Electron Microscopy of Multilayer Heteroepitaxial Semiconductors

Abstract

ABSTRACTThin-film epitaxial layers on silicon substrates are being actively developed as an alternative to bulk substrates for infrared detectors. Success in this development is expected to yield improvements in size, strength, monolithic signal processing, and cost of the detector arrays. To provide feedback to the thin-film growth process, this study has investigated the structural and chemical properties of these films. CdTe or CdZnTe was grown on GaAs on Si wafers by metalorganic chemical vapor deposition (MOCVD) followed by the growth of HgCdTe by liquid-phase epitaxy (LPE). Development of TEM specimen preparation techniques permitted investigation of materials with up to four layers. Cross sectional TEM and AEM investigations resulted in the following observations: Selected area diffraction and CTEM show relations between the layers and structural defects. High resolution imaging of the multilayers reveals that most of the heteroepitaxial misfit is accomodated by misfit dislocations. Many, but not all, stacking faults and dislocations which propagate across the films appear to be related to structural interface defects. The evidence indicates that there is little, if any, contamination at MOCVD and LPE interfaces. Interface defects mainly appear to be extremely minute pits or hillocks. AEM investigations of interface regions have demonstrated a redistribution of material close to the CdZnTe / HgCdTe interface.