Y.S. Ryu

Optical and electrical properties of in situ-annealed p-type Hg0.7Cd0.3Te epilayers grown on CdTe buffer layers for applications as infrared detectors

Hall-effect, Fourier transform infrared (FTIR) transmission, and photopresponse measurements were performed to investigate the optical and electrical properties of as-grown and in situ-annealed Hg0.7Cd0.3Te epilayers grown on CdTe buffers on GaAs (211) B substrates layers by using molecular-beam epitaxy. Hall-effect measurements showed that as-grown n-Hg0.7Cd0.3Te epilayers were converted to p-Hg0.7Cd0.3Te epilayers due to in situ annealing. The carrier concentration and the mobility as functions of the annealing temperature were determined from the Hall-effect measurements. The FTIR spectra showed that the transmission intensity had increased in comparison to that of the as-grown Hg0.7Cd0.3Te epilayer. Hall-effect measurements showed that n-Hg0.7Cd0.3Te epilayers were converted to p-Hg0.7Cd0.3Te epilayers. The activation energy and the carrier lifetime of the annealed Hg0.7Cd0.3Te epilayer were 0.25 eV and 160 ns, respectively. These results indicate that p-type Hg0.7Cd0.3Te epilayers grown on CdTe buffe...

Semiconductor quantum dots created by postgrowth treatment

Abstract Semiconductor nanometer-scale dots were created by postgrowth hydrogen treatment of GaN films grown on sapphire and silicon substrates with AlN or GaN buffer layers and CdTe and HgCdTe films grown on CdZnTe substrates. HRSEM and AFM measurements confirmed that the nanometer-scale dots were formed by the treatment both on flat and inclined faces regardless of a lattice mismatch between the materials used. Changing hydrogenation conditions controls a density and size of the dots. The blue-light emissions observed from GaN quantum dots were attributed to the presence of a piezoelectric field in the dots.

Improvement in the crystallinity and electrical properties in Hg 1− x Cd x Te epilayers utilizing CdTe buffer layers grown on GaAs substrates by a two-step annealing process

High-quality Hg 1 - x Cd x Te epilayers on CdTe buffer layers were grown by molecular beam epitaxy using various growth methods. The reflection high-energy electron diffraction, scanning electron microscopy, and atomic force microscopy measurements showed that the crystallinity and electrical properties of the Hg 1 - x Cd x Te epilayers grown on CdTe buffer layers deposited by using a two-step annealing growth method were improved. These results indicate that high-quality Hg 1 - x Cd x Te films can be obtained by using CdTe buffer layers grown by the two-step annealing growth method and that the grown Hg 1 - x Cd x Te epilayers hold promise for potential applications in optoelectronic devices in the area of infrared detectors.

Effect of lattice mismatch and thermal expansion on the strain of CdTe/GaAs heterostructures

Photoluminescence (PL) measurements on CdTe/GaAs heterostructures grown by molecular beam epitaxy (MBE) were carried out to investigate the effect of the lattice mismatch and the thermal expansion on the strain due to the CdTe epitaxial layer thickness in CdTe/GaAs heterostructures. The PL peak of the acceptor bound exciton shifts toward the higher-energy side with increasing CdTe film thickness. A new theoretical equation obtained from the strain on the lattice-mismatched heterostructure is proposed. The values of the strains determined from the PL measurements were in reasonable agreement with those determined from the new theoretical calculations taking into account the lattice mismatch together with the thermal expansion difference between the CdTe epilayers and the GaAs substrates. These results can help improve the understanding of the structural properties of CdTe/GaAs heterostructures.

Rapid thermal annealing effects in CdTe (111) thin films grown on Si (100) substrates by molecular beam epitaxy

Abstract Photoluminescence (PL) measurements have been carried out to investigate rapid thermal annealing (RTA) effects in CdTe (111) epilayers grown on Si (100) by molecular beam epitaxy, The full width at half maximum (FWHM) of the bound exciton peak of the PL spectrum for the as-grown CdTe layer was 20 meV. When RTA was performed at 400°C, the bound exciton peak was resolved into two bound exciton peaks due to neutral acceptors ( A°, X) and to neutral donors (D°, X) and one free exciton peak; the FWHM of the ( A°, X) peak was as small as 3.7 meV. When RTA was carried out at 600°C, the relative intensity ratio between the luminescences related to the defects and (A°, X) in the as-grown and the annealed CdTe layers decreased by a factor of 15. The activation energy of the ( A°, X) peak as obtained from temperature-dependent PL measurements was 18.7 meV. The bound exciton peak for the CdTe, which was rapidly thermally annealed at 400°C, shifted by 7.5 meV in comparison with that for the CdTe bulk, and the strain obtained from the PL peak shift was −0.0286, These results indicate that the crystallinity of the CdTe epilayers grown on Si is improved by RTA and that the RTA CdTe films grown on Si can be used for applications as buffer layers for the growth of Hg x Td 1−x Te.

Improvement of the crystallinity of CdTe epitaxial film grown on Si substrates by molecular beam epitaxy using the two-step growth method

Abstract Molecular beam epitaxy growth of CdTe epitaxial layers on Si (100) substrates using the two-step growth method was performed to produce high-quality CdTe thin layers. The reflection high-energy electron diffraction patterns were streaky with clear Kikuchi lines, which is direct evidence for layer-by-layer two-dimensional growth of CdTe on Si. From the X-ray diffraction analysis, the grown layer was found to be a CdTe (111) epitaxial film,regardless of the film thickness. Photoluminescence (PL) measurements at 12 K showed that the defect density of the CdTe film grownon Si using two-step growth decreased in comparison with that grownusing direct growth. The bound exciton appearing in the PL measurements shifted to the low energy side as the thickness of the CdTe increased. When the CdTe thickness increased from 1 to 1.8 μm, the peak position of the bound exciton shifted by 7.2 meV, and the stress obtained from the exciton peak shift was - 12.405 kbar. These results indicate that high quality CdTe films grown by two-step growth hold promise for applications as buffer layers for the subsequent growth of Hg x Cd 1− x Te.