S. Sivananthan

High quality large-area CdTe(211)B on Si(211) grown by molecular beam epitaxy

We describe the growth of high quality CdTe(211)B layers by molecular beam epitaxy on nominal Si(211) substrates. Prior to CdTe deposition, thin ZnTe(211)B buffer layers were grown to preserve the homo-orientation. Large-area CdTe(211)B layers were routinely obtained by optimizing the growth parameters. From x-ray diffraction, we observed the presence of twin-free CdTe(211)B layers. One 8 μm thick CdTe epilayer had a near-surface etch pit density of 1.5×105 cm−2, which surpassed the best value reported for CdTe(211)B grown on GaAs(211)B, GaAs/Si(211), or Si(211) substrates.

Atomic layer graphoepitaxy for single crystal heterostructures

Here we report a strategy for the growth of single crystal heterostructures that dramatically reduces the nucleation of defects at the film–substrate interface. The substrate surface is patterned through miscut and passivated to enable a single domain template layer to be grown. This template is incommensurate with, and weakly bonded to, the substrate. A single domain film can then be nucleated preferentially at step edges and grown on the template. This mechanism is demonstrated for CdTe on Si(100) and should be applicable to many other systems.

Hot electron relaxation dynamics in ZnSe

The ultrafast relaxation dynamics of hot electrons, initially photoexcited with an excess energy of 300 meV, are monitored in a high-quality ZnSe epilayer grown on a GaAs substrate by exploiting the intrinsic interferrometric asymmetric Fabry–Perot sample structure. The results are consistent with the expected characteristic electronic LO-phonon emission time of 40–50 fs and provide evidence for the influence of the “hot phonon effect”(or “LO-phonon bottleneck”) on the electron cooling dynamics at carrier densities above ∼3×1017 cm−3.

P-type doping with arsenic in (211)B HgCdTe grown by MBE

Arsenic incorporation and doping in HgCdTe layers grown by molecular beam epitaxy (MBE) were examined in this paper. Arsenic incorporation into MBE-HgCdTe was carried out in two different ways: (1)ex-situ arsenic ion-implantation on indium-doped n-type HgCdTe layers, and (2) through a new approach called arsenic planar doping. We report onex-situ arsenic diffusion on indiumdoped MBE-HgCdTe layers at 450°C. In the investigated layers, arsenic redistribution occurs with a multi-component character. We obtained a diffusion coefficient of DAs = (1-3) × 10−13 cm2/s at 450°C. Results of differential Hall and fabricated p-n junctions suggest that during high temperature annealing, arsenic preferentially substitutes into Te sublattices and acts as acceptor impurities. In the second case, arsenic has been successfully incorporated during the MBE growth as an acceptor in the planar doping approach. Withoutex-situ annealing, as-grown layers show up to 50% activation of arsenic during the growth. These results are very promising forin-situ fabrication of infrared devices using HgCdTe material.

Reflectivity difference spectroscopy study of thin film ZnSe grown on GaAs by molecular beam epitaxy

Abstract ZnSe films were grown on GaAs substrates with various growth conditions by molecular beam epitaxy (MBE). The optical anisotropy of the films was determined by reflectivity difference spectroscopy (RDS) during and/or after growth. Comparison of the in situ RDS data with spectroscopic ellipsometry (SE) data suggests that RDS could be utilized to determine film thickness, alloy composition and temperature during growth. The RDS spectra were also compared with results from transmission electron microscopy (TEM), X-ray double-crystal rocking curve (DCRC) and Hall measurements. Comparison with the Hall effect showed that the magnitude of the optical anisotropy is generally larger for higher carrier concentrations. Comparison with TEM results and the full-width-at-half-maximum measurements by DCRC reveals that: (i) the E1 structure arising from the bulk spatial distribution (BSD) is correlated with film quality; (ii) the amplitude of the interference below E0 provides a measure of the ZnSe GaAs interface quality; and (iii) the large anisotropy above the band gap is correlated with surface roughness.

Optical investigation of strain and defects in (100) CdTe/Ge/Si and ZnTe/Ge/Si grown by molecular beam epitaxy

Low temperature (1.7 K) reflectance and photoluminescence (PL) have been used to assess residual strain and impurities in molecular beam epitaxial (100) CdTe/Ge/Si and (100) ZnTe/Ge/Si. Both types of samples exhibit residual biaxial tensile thermal strain as expected from differences in previous thermal expansion data, but the measured magnitudes (0.72×10−3 for CdTe/Ge/Si and 1.5×10−3 for ZnTe/Ge/Si) are smaller than predicted. The results are consistent with either residual lattice mismatch stress or partial relaxation of the thermal strain during cooling. Residual acceptors in the CdTe include Cu and a frequently observed 49 meV level, whose PL peaks lack the previously reported linear polarization. However, a new series of linearly polarized bound exciton lines is reported in CdTe.

Molecular beam epitaxial growth of ZnSe on GaAs substrates : influence of precursors on interface quality

The initial growth of thin ZnSe layers, grown on GaAs(0 0 1) using molecular beam epitaxy (MBE), has been studied using real-time reflection high-energy electron diffraction (RHEED), as well as X-ray double-crystal rocking curves (DCRC), reflectivity difference spectroscopy (RDS) and transmission electron microscopy (TEM). A noticeable difference in interface quality and growth was observed depending upon the initial precursor. Exposure to Se flux before growth led initially to three-dimensional growth, whereas exposure to Zn flux or no precursor led immediately to two-dimensional growth. X-ray DCRC and RDS confirmed that the overall sample quality was better with two-dimensional growth, and TEM observations were consistent with previous studies which have shown that initial three-dimensional growth is related to the formation of Ga2Se3 at the interface, leading to high densities of stacking faults and edge dislocations.

Two-Dimensional Excitons in A Strongly Localized Regime in CdTe/ZnTe Superlattices

Time-resolved spectroscopy of the recombining exciton state in a highly strained II-VI semiconductor superlattice CdTe/ZnTe reveals strong localization effects at low lattice temperatures. Such phenomena originate naturally from small deviations in structural perfection on a monolayer scale in a strained superlattice with a small valence band offset. The quasi-2D aspect enhances the localization phenomena further.