Yasuo Okuno

Blue light emission from ZnSe p‐n junctions

Pure blue light emission has been obtained from ZnSe p‐n junctions. ZnSe crystals are grown by the temperature difference solution growth method under controlled vapor pressure. A p‐type ZnSe crystal can be grown from Se solution by doping with a group I element under controlled Zn pressure. The properties of p‐type crystals have been measured by the van der Pauw method. A p‐n junction has been made by the formation of the n‐type layer by Ga diffusion into the p‐type crystal. The fundamental properties of the p‐n junctions are as follows: the value of n in the I‐V characteristics ranges from 1.4 to 1.8 and the diffusion potential is between 2.5 and 2.7 eV. The emission spectrum from the p‐n junction depends on the vapor pressure during growth and blue light emission is obtained with optimum pressure. The wavelength of the main emission peak is 460 nm at 77 °K and 480 nm at 300 °K. The brightness is 2 mcd at 2 mA.

Nearly perfect crystal growth of III–V compounds by the temperature difference method under controlled vapour pressure

Nearly perfect crystals of III–V compounds are grown by a new LPE method which can produce homogeneous and high-quality crystals with controlled stoichiometry. Homogeneous epitaxial growth is performed at fixed temperature with a temperature difference in a melt, under controlled vapour pressure of the group V elements. In the experiment, the fluctuation of growing temperature is ascertained to produce a number of new defects and the effect of controlled vapour pressure is investigated. It has been ascertained that an optimum vapour pressure, which is the function of growing temperature, can suppress the generation of “rooty faults” to a minimum density. There is close agreement between the optimum vapour pressure in the heat treatment of crystals to reduce the generation density of lattice defects and the optimum vapour pressure to obtain defect-free crystals in the process of crystal growth. The epitaxial layers prepared under optimum vapour pressure have the highest mobility and the lowest additional carrier concentration. The lattice constant of the epitaxially grown crystal under controlled vapour pressure also shows a minimum value at optimum pressure. This also shows that the controlled vapour pressure is important in lattice fitting of epitaxial layers. The epitaxial layers grown by the temperature difference method (TDM) under optimum control of the vapour pressure (CVP) are almost as perfect crystallographically as measured by X-ray topography. The experiments are performed for GaP and GaAs.

p‐type conduction in ZnSe grown by temperature difference method under controlled vapor pressure

Electrical properties of a low‐resistive and stable p‐type ZnSe crystal grown by the temperature difference method under controlled vapor pressure are reported. The temperature dependence of Hall mobility, carrier (hole) concentration, and conductivity are measured by the van der Pauw method. Hole mobility appears to be about 200 cm2/V s at 100 K and about 50 cm2/V s at 300 K. The activation energy of a shallow acceptor impurity is also determined to be 70–85 meV.

GaAs TUNNETT Diodes

The tunnel-injection-transit-time (TUNNETT) diode is operated at a high frequency and has a low-noise level compared to the IMPATT diode. The tunnel injection in a thin carrier generating region of the TUNNETT depends strongly on the electric-field intensity over 1000 kV/cm where the ionization of carriers can be neglected, leading to a higher efficiency performance than that of the IMPATT. GaAs TUNNETT diodes with p+-n and p+-n-n+ structures have been fabricated by a new LPE method (the temperature-difference method under controlled vapor pressure). The fundamental oscillation at frequencies from about 100 up to 248 GHz has been obtained from the pulse-driven p+-n-n+ diodes. This paper describes the details of the oscillation characteristics of GaAs TUNNETT diodes.

Balance method for experiments under controlled vapor pressure.

A new thermo-balance has been developed for measuring the vapor pressure of molten substances at high temperatures. The accuracy of mass measurements of the balance is higher than 0.1 mg for a sample of 10 g. The balance has been used to determine the molecular number of arsenic gas. Also, by slight modification, the balance can be used in the experiments under controlled vapor pressure for measuring other quantities, such as diffusion constants of various gases.

Bright Pure Green Emission from N-free GaP LED's

The pure green emission with high external efficiency of 0.12% has been obtained in nitrogen free GaP LED grown by applying the optimum phosphorus pressure at a constant temperature solution growth. The high efficiency N-free LED has a p+n- structure and the peak emission wavelength is 5560 A at room temperature. The minority carrier lifetime is 1.4 µsec. The crystalline quality has been improved under the optimum phosphorus pressure and the concentration of deep levels in GaP decreases. Therefore, the minority carrier lifetime becomes longer, and the high efficiency pure green GaP LEDs have been produced.

Deep levels studies of N-free and N-doped GaP grown by TDM-CVP.

The energies and densities of deep levels in N-free and N-doped GaP LED depend on the applied phosphorus pressure during epitaxial growth. Especially, the deep level in N-free GaP located at EC-ET=0.65 eV strongly affects the brightness of emission and has close correlation with the shallow donor concentration in the n layer. The deep levels in N-doped GaP are complicated and their energies change according to the phosphorus pressure. Some of the deep levels in N-doped GaP are proposed for the complex of nitrogen.

Deep levels in GaP

Change of the junction capacitance under the illumination of monochromatic radiation has been observed in GaP n+p junctions. The peaks were observed at 1.8 and 2.4 eV at 77°K. The 1.8 eV peak was attributed to the hole activation from Fe3+ to the valence band. The photoconductivity spectrum and the transient phenomenon of the photoconductivity in p+n junctions and in high‐resistivity n‐type bulk crystals also showed the presence of the 1.8 eV level due to Fe.

Observations of defects in LPE GaAs revealed by new chemical etchant

Abstract The behavior of dislocations in the interfacial region between the epitaxial layer grown from the liquid phase and the substrate of GaAs is investigated. Observations of dislocations lying along the 〈110〉 directions were carried out using an optical microscope after shallow etching with a new chemical etchant. The dislocations are traced by the repetition of etching from epitaxial layer to the interface. The results show that dislocations in the substrates are expected to bend along the direction normal to the epitaxial growth direction at the interface.

Heat treatment of gallium phosphide

Abstract Annealing effect of GaP depends on the phosphorus pressure observed by Hall effect, X-ray diffraction and photoluminescence. The phosphorus pressure for the peaks of the lattice constant after annealing coincide with that for the high resistivity in the Hall measurement.