K. Hirahara

Superiority of group VII elements over group III elements as donor dopants in MOCVD ZnSe

Abstract Comparison of group III and group VII elements as donor species in ZnSe MOCVD growth has been studied from the viewpoint of their electrical properties, luminescence qualities and their controllabilities. Low resistivity high quality blue emitting ZnSe has been grown by doping a group VII donor chlorine, in atmospheric MOCVD. The superiority of group VII elements over group III elements with regard to carrier concentration controllability and carrier producing efficiency has been predicted.

Quantitative photoelastic measurement of residual stress in LEC grown GaP crystals

Abstract The characterization of GaP crystals, grown by the liquid encapsulated Czochralski method, has been accomplished by means of a quantitative photoelastic technique. Two kinds of radiation with wavelengths, 0.55 and 1.1 μm, are effectively used to determine the isochromatic line corresponding to the zeroth order of retardation. Residual stress is determined by using piezo-optical coefficients calculated in various coordinate systems. It has been found that the diameter control of crystals is effective to reduce the residual stress, and also that the crystallographic symmetry of principal stress lines is related with the pulling direction of the crystal.

The zinc pressure effect in chlorine-doped ZnSe grown by atmospheric metalorganic chemical vapor deposition

An n‐type ZnSe has been grown by atmospheric metalorganic chemical vapor deposition in which hydrogen chloride was used as the chlorine‐donor source. Epitaxial layers were evaluated by photoluminescence measurements and Hall measurements. An excitonic emission intensity at 4.2 K, which is a donor bound excitonic emission, increased with donor doping concentration increase. The electron carrier concentration varied with a quadratic dependence on the dopant concentration. Chlorine‐doped ZnSe characteristics were revealed to be similar in regard to the relation between the electrical and luminescent properties, irrespective of dopant source materials. An increase in zinc partial pressure led to an increase in carrier concentration and the suppression of the self‐activated emission intensity. A zinc excess growth condition was revealed to be effective for quality improvement for n‐type ZnSe and suppression of the compensation effect, which made the carrier producing efficiency high.

p-type carrier concentration control in lithium-doped zinc selenide grown by MOCVD

Abstract Lithium-doped ZnSe epitaxial layers have been grown on GaAs substrates by metalorganic chemical vapor deposition. Tert-butyllithium (TBL) was used as a doping material. Secondary ion mass spectroscopy showed that Li concentrations in ZnSe layers could be altered from 4×10 17 to 4×10 17 cm -3 by variation of the carrier gas flow rate passing through the TBL cylinder. Photoluminescence measured at 4.2 K indicated acceptor concentration increased with TBL carrier gas flow rate. Carrier concentrations N A − N D obtained from C − V measurements increased to about 1×10 15 cm -3 with increasing TBL carrier flow rate.

Confirmation of P-Type Conduction in Li-Doped ZnSe Layers Grown on GaAs Substrates

Hall effect measurements were carried out for Li-doped MOCVD ZnSe layers whose GaAs substrates were removed. This made it possible to obtain the original p-type properties for the layers. Hole concentration, Hall mobility and specific resistivity were 4.1×1016 cm-3, 24 cm2/V s and 6.4 Ωcm, respectively. Furthermore, the characteristics for the GaAs inversion layers, which were changed from semi-insulating to p-type by Zn diffusion from the ZnSe layers, were estimated by comparing the results of samples without GaAs substrates with those with GaAs substrates.

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.

Lattice matching effect on the luminescent properties of n-ZnSSe on GaAs grown by MOCVD

Abstract Lattice matching effects on Br-doped ZnSSe/GaAs system were studied. A homogeneous image was observed in the lattice matched system ZnS 0.09 Se 0.91 /GaAs by SEM cathodeluminescence (CL), whereas there were many dark spots on CL images for the lattice mismatched ZnSe/GaAs system. The dislocation density on the (100) surface was estimated as 10 8 cm -2 from TEM cross sectional images and 10 7 cm -2 by etch-pit measurement in the lattice mismatch system. The dislocation density decreased to below 10 6 cm -2 from TEM estimation and 10 4 cm -2 from EPD measurement by lattice matching. The photoluminescence (PL) intensity at room temperature for lattice matched ZnSSe was about 10 times larger than that for lattice mismatched ZnSe with the same doping concentration ( n =10 16 cm -3 ). These studies proved that precise lattice matching is needed to obtain crystals which have a high luminescence efficiency.

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.