No abstract

InP epilayers with different thicknesses were grown on GaAs substrates at a low temperature by using metalorganic chemical vapor deposition. Atom force microscope and double-crystal X-ray were carried out to investigate the morphology and the crystal quality. Transmission electron microscopy was performed to characterize the microstructure and morphology. It was found that with the epilayer thicknesses increased, the crystal quality was improved and the dislocations in epilayers were decreased. Moreover, the sample that has 150-nm InP epilayer could observe large numbers of antidislocations in the gallium arsenide substrate. The formation mechanism of antidislocations was also discussed with the analysis of crystal structure and surface morphology. Furthermore, we proposed a mechanism to explain the motion and the reaction of antidislocations. It is necessary to grow InP epilayers on GaAs or Si substrates by using mature fabrication process to obtain the big size InP film. [11][12][13][14] Antiphase domain observed in polar on nonpolar system in InP/Si heterostuctures can be avoided in InP/GaAs heterostuctures. So, GaAs material was used as substrates in this work. However, the InP/GaAs heterostuctures have 4% lattice mismatch, which results in high dislocation density when the thickness of InP epilayers reaches the critical thickness of 5 nm. 15 The dislocation was the primary problem because the crystal quality of materials was seriously affected by the big lattice mismatch. In this work, we grew InP epilayers with different thicknesses on GaAs substrates by metalorganic chemical vapor deposition (MOCVD) at a low temperature. The aim was to explore the generation and the distribution of dislocations. Simultaneously, it was analyzed how the dislocations were affected by the epilayer thicknesses by investigating surface morphology and crystal quality. | EXPERIMENTALThe MOCVD system was used to grow InP/GaAs heterostructures. Phosphine (PH 3 ) was employed as the protective atmosphere.Trimethylindium (TMI) and PH 3 were used as group III and V source materials, respectively. The GaAs (100) substrates were chemically cleaned for 10 minutes to remove the oxide layer. After that, InP with different thicknesses (50, 150, and 400 nm) were grown on GaAs substrates at a relatively low temperature (430°C), which were labeled as samples A, B, and C, respectively.Atomic force microscope was carried out to evaluate the surface morphology and roughness. Raman spectra and DCXRD (doublecrystal X-ray diffraction) were used to investigate the crystal quality.Transmission electron microscopy was performed to examine the microstructure of InP-GaAs surface and the distribution of dislocations caused by the large lattice mismatch. The Hall effects were used to investigate the performance of InP/GaAs heterostructures with different thicknesses.

Zinc-substituted hydroxyapatite (Zn-HA, Ca 10-x Zn x (PO 4) 6 (OH) 2) is used as the modified material of hydroxyapatite (HA, Ca 10 (PO 4) 6 (OH) 2). In this work, Zn-HA with Zn contents of 10-30 mol% was used to produce Zn-HA/Mg composites by powder metallurgy. The calculated results showed that the crystallite size and lattice parameters of Zn-HA powders varied with the contents of 0-30 mol% Zn, confirming that the divalent Zn 2+ ions can substitute Ca 2+ ions in HA. Furthermore, the microstructure, mechanical property and electrochemical corrosion behavior of Zn-HA/Mg composites were investigated by SEM, compression tests, and electrochemical corrosion tests, respectively. The results indicate that the highest density and lowest porosity are obtained and the optimal mechanical property and corrosion resistance are achieved in the Zn-HA/Mg composites with 20 mol% Zn.