Takao Kawanaka

Study on the ZnSe phase diagram by differential thermal analysis

Abstract The liquids line and the temperature of the solid-solid phase transformation of the system ZnSe near the stoichiometric composition were determined by the modified differential thermal analysis (DTA) technique. The congruent melting point ( T m ) of ZnSe was determined to be 1522 ± 2°C, i.e., within the range of the already reported values. The 2H to 3C solid-solid phase transformation temperature is 1411 ± 2°C, 14°C below the reported values. The shape of the observed liquidus line was compared with the theoretical quasiregular and regular associated solution models. It correlates well with the latter solution model, suggesting the existence of associated molecules in the ZnSe melt.

Melt growth of ZnSe single crystals with B2O3 encapsulant: the role of solid-solid phase transformation on macro defect generation in ZnSe crystals

Abstract B 2 O 3 is an available encapsulant for the melt growth of ZnSe single crystals with a limited degree of contamination of boron, 10 16 −6 × 10 18 atmos cm −3 . It is effective to reduce the density of twins in ZnSe crystals. Through the consideration of the role of B 2 O 3 encapsulant, the generation process of three specified structures of melt-grown ZnSe crystals was interpreted. It is attributed to the different solid-solid transformation mechanisms governed by the nucleation process of the zincblende phase.

The origin of shallow etch pit defects in low dislocation density GaP crystals

The defect corresponding to shallow etch pits (S-pits) on GaP wafer has been revealed. It is a vacancy-type Frank dislocation loop which surrounds a stacking fault. It is proposed that this loop is formed by the condensation of excess gallium vacancies during cooling of the GaP crystal. The phosphorus precipitates on the dislocation loop result from the condensation of the emitted phosphorous interstitials accompanied by the growth of the loop. Stoichiometry control is necessary to suppress the formation of S-pit defects in low dislocation density compound semiconductor crystals.

Photoluminescence study of ZnSe single crystals melt-grown with B2O3 encapsulant

Abstract Some properties of ZnSe single crystals grown from melt using a B 2 O 3 encapsulant were investigated. B 2 O 3 encapsulation prevents the crystal from contamination of impurities during growth and improves the crystallinity, specifically by subsequent annealing at 1390°C. However, it is revealed that the concentration of boron in the ZnSe crystal is increased by using B 2 O 3 encapsulant. At the same time, the photoluminescence spectrum of the annealed sample shows characteristic emission peaks at 2.733 and 2.752 eV at 16 K by 16 mW cm −2 excitation of 325 nm emission line from a He-Cd laser. From both the temperature dependence and the excitation intensity dependence of the peak energy, these emissions are identified as a donor-acceptor pair and a conduction-band-to-acceptor emission, respectively. A shallow acceptor level is located at about 70 meV above the valence band. From the facts that the crystal contains 10 17 –10 18 atoms cm −3 of oxygen as an impurity and the formation of this level correlates to the annealing process, isoelectronic oxygen or oxygen associated complex is believed to be a possible origin of the shallow level.

Formation of a defect-free denuded zone in GaP substrate by thermal annealing

The vacancy-type Frank dislocation loops in GaP, which are the origin of shallow etch pit defects, dissolve during heat treatment via outdiffusion of the originating point defects. This forms a defect-free denuded zone under the surface of a GaP wafer. The activation enthalpy of the diffusion process of the gallium vacancy (which corresponds to the formation of the denuded zone) is estimated to be 4.0 eV.