Keitaro Shigenaka

Orientation dependence of HgCdTe epitaxial layers grown by MOCVD on Si substrates

Orientation dependence of HgCdTe epilayers grown by MOCVD on Si substrates was studied. Substrate orientation is considered to be one of the most sensitive factors to enable hetero-epitaxial growth on silicon substrates, especially in the case of a low temperature growth process. The present work was carried out with characterized features of a low temperature process for HgCdTe growth on Si and using a thin CdTe buffer layer. The (100), (100) misoriented toward [110], (311), (211), (111), and (331) oriented Si substrates were used in the present work. The best results were obtained on (211)Si substrates with an x-ray full width at half maximum of 153 arc sec for a 5 (im thickness HgCdTe layer and 69 arc sec for a 10 um thickness layer. It was found that the effective lattice mismatch of CdTe/Si heterosystem was reduced to 0.6% (for the 611 lattice spacing of CdTe and 333 spacing of Si) in the case of (133)CdTe/(211)Si.

Misfit dislocation microstructure and kinetics of HgCdTe/CdZnTe under tensile and compressive stress

Abstract The effects of interfacial lattice mismatch upon Hg1-xCdxTe epitaxial layers grown by metalorganic chemical vapor deposition (MOCVD) were investigated. HgCdTe was found to be easily affected by lattice mismatch of less than ±0.1%. It has been shown that mismatched HgCdTe layers in tension tend to deteriorate more easily than those in compression. This asymmetric phenomenon was explained using a schematic model of the lattice structure. The asymmetric phenomenon is attributable to the asymmetric dislocation distribution due to the presence of excess mercury vacancies in addition to the sign of the misfit strain and the different lattice structure.

Effects of growth rate and mercury partial pressure on twin formation in HgCdTe (111) layers grown by metalorganic chemical vapor deposition

The relationship between twin formation and the growth conditions for (111) HgCdTe epitaxial layers grown by metalorganic chemical vapor deposition was investigated. The existence of twins was confirmed by x-ray diffraction and cross-sectional transmission electron microscopy. The x-ray diffraction intensity of the 180°ø rotated 422 asymmetric reflection with that of the 422 asymmetric reflection was compared to detect the presence of twins. The layer obtained using a low growth rate and a low Hg partial pressure showed double-positioning (DP) twins. The twins became lamellar as the growth rate increased. Twin-free HgCdTe epitaxial layers were obtained under a high growth rate and a high Hg partial pressure. These results suggest a model for twin formation based on the difference in the growth mechanism of HgTe and CdTe. Twin-free (111) HgCdTe epitaxial layers were reproducibly obtained without using inclined substrates by optimizing the growth conditions by using this model.

Influence of Lattice Mismatch on the Electrical and Structural Properties of HgCdTe Epilayers

The influence of lattice mismatch on the electrical and structural properties of HgCdTe epilayers grown on CdZnTe substrates has been investigated. A slight lattice mismatch of the order of less than ±0.1% between the epilayer and the substrate brings about a conductivity-type conversion of HgCdTe layers, which is related to the presence of misfit dislocations. It is considered that the conductivity-type conversion is caused by diffusion of impurities from the substrate to the epilayer due to the high interface dislocation density. This work emphasizes the importance of minimizing the interactions between the epilayer and its substrate by the precise lattice-matching.

Lattice relaxation in large mismatch systems of (111)CdTe/(100)GaAs and (133)CdTe/(211)GaAs layers

Abstract Differences between the progress of lattice relaxation in (111)CdTe / (100)GaAs and (133)CdTe / (211)GaAs heterostructures, in which large 14.6% lattice mismatches exist, were revealed by lattice images obtained by transmission electron microscopy and photoluminescence spectra of the layers. The lattice of the (133)CdTe layers on the (211)GaAs substrates rotated to relax misfit strains around the 〈011〉 axis which was perpendicular to the growth direction and parallel to the 〈011〉 axis of the substrate. On the other hand, the lattice of the (111)CdTe layers on the (100)GaAs substrates rotated around the 〈111〉 axis parallel to the growth direction, because the glide plane of (111)CdTe was inconsistent with that of (100)GaAs. Our findings suggest that CdTe layers of higher structural quality are obtainable on (211)GaAs substrates than on (100) oriented substrates.

Achievement of low p-type carrier concentration for MOCVD growth HgCdTe without an annealing process

The electrical characteristics of as-grown epitaxial HgCdTe layers grown by metalorganic chemical vapor deposition were investigated. We propose a new cap layer in order to obtain as-grown HgCdTe layers with low p-type carrier concentration. The new cap layer called the double-cap layer consists of a graded Cd content Hg 1-x Cd x Te layer with x = 0.2-0.7 and a CdTe cap layer which was continuously grown at low temperature on the graded HgCdTe layer. The carrier concentration of HgCdTe layers with the new cap layer was about 3 x 10 16 cm -3 .The p-type carrier concentration has been reduced further to 2 x 10 15 cm -3 (for x = 0.22) by lowering the growth temperature and increasing the partial pressure of Hg. This carrier concentration is lower than the estimated Hg vacancy concentration from considerations of the thermal equilibrium conditions.