HgTe-CdTe Superlattices Grown by Photo-MOCVD

Abstract

ABSTRACTHgTe-CdTe superlattices have been grown, for the first time, by photoassisted MOCVD. The substrate temperature was 182°C. Superlattices were obtained despite low growth rates requiring long growth times (∼10 hours). Interdiffusion during growth may be slowed down by growing under saturated Hg vapor to minimize cation-vacancy formation. The nominal superlattice structures were 70Å HgTe-30Å CdTe, 40Å HgTe-40Å CdTe, and similar. Actual superlattice structures were verified by cross-sectional TEM and diffractometer x-ray diffraction patterns. The x-ray diffraction patterns showed satellite peaks up to third order. The actual structures had HgTe layers ∼20% thicker than the nominal (target) values. A grid-like array of dislocations at the substrate-epilayer interface, suggesting operation of a dislocation-blocking mechanism, was observed. Deficiencies in the superlattice growths include a low growth rate, nonuniform layers, high dislocation density (∼108 cm−2 in best layers), and high n-type carrier concentration (∼1018 cm−3 with mobilities up to 3.5 × 104 cm2 V−1 s−1 in the best layer) which may reflect the presence of donor impurities in the material.