Katsumi Yagi

Suppression of Cu diffusion from a bulk ZnSe substrate to a homoepitaxial layer by Se‐beam irradiation as a pregrowth treatment

Cu diffusion of homoepitaxial ZnSe was investigated through low‐temperature photoluminescence (PL) spectra and secondary ion mass spectroscopy. Though Cu in ZnSe normally diffuses easily, we found that Cu in a ZnSe substrate did not diffuse into the homoepitaxial layer when the substrate was heated under Se‐beam irradiation prior to growth. Cu‐related emissions, such as Ideep1 and Cu‐green, disappeared from the PL spectrum of the homoepitaxial layer grown on the Se‐beam irradiated substrate. This suppressed Cu diffusion can be explained by site transformation of interstitial Cu atoms in the ZnSe substrate into Cu atoms occupying the Zn lattice site. This treatment is very useful for improving the purity of homoepitaxial ZnSe layers.

Fabrication of GaAs/AlGaAs GRIN-SCH Lasers with Newly Developed Ridge Waveguide

In this paper, a new ridge fabrication method is demonstrated. The upside cladding region is composed of two different Al mole fraction AlGaAs layers which have been selectively etched to form a ridge waveguide. GaAs/AlGaAs graded-index waveguide separate-confinement heterostructure (GRIN-SCH) lasers with this newly developed ridge waveguide have shown high external differential quantum efficiencies, with a maximum of 80% for a 4 µm × 250 µm cavity.

P-Type Conducting ZnSe and ZnSSe by N2-Gas Doping During Molecular Beam Epitaxy

Highly conductive p-ZnSe and ZnSSe can be grown by N2-gas doping without any activation process during molecular beam epitaxial growth. Photoluminescence spectra indicated that the properties of N2-gas- and nitrogen-radical-doped ZnSe with nearly equal N A -N D are almost the same. Using the N2-gas doping method, the first laser oscillation from a ZnSe-based laser diode without nitrogen-radical doping was achieved. The LED driving voltage was 3.8 V at the operating current of 20 mA.

Molecular beam epitaxy of p‐type conducting ZnSe and ZnSSe by simple nitrogen gas doping without plasma activation

Highly conducting p‐type ZnSe and ZnSSe were fabricated by simple N2 gas doping during molecular beam epitaxial growth without the use of any activation method, such as discharge and cracking. p‐type conduction in the N2‐gas doped ZnSe is produced by a shallow N acceptor state, which is obtained only when the dopant N2 pressure is higher than 10−5 Torr. When the N2 pressure was varied from 3.2×10−5 to 1×10−4 Torr, the net acceptor concentration of N2‐gas doped ZnSe and ZnS0.06Se0.94 films ranged from 3×1015 to 2×1017 cm−3 and from 1×1016 to 2.5×1017 cm−3, respectively. Light emitting diodes with a N2‐gas doped p‐cladding layer were fabricated and tested.

Room Temperature Pulsed Oscillation of GaAlAs/GaAs Surface Emitting Junction Laser Grown by MBE

GaAlAs/GaAs surface emitting (SE) junction lasers have been fabricated by molecular beam epitaxy (MBE). It is easy for the MBE method to obtain a good flatness of grown surfaces to be utilized as reflective mirrors, and to control the thickness of the grown layer more precisely, compared with liquid phase epitaxy (LPE). We report on the room-temperature pulsed oscillation of a SE laser grown by MBE. The threshold current was as low as 450 mA, and single-mode operation was achieved at λ = 8735 A.

P- Type Conducting ZnSe and ZnSSe by N2-Gas Doping during Molecular Beam Epitaxy

Highly conductive p-ZnSe and ZnSSe can be grown by N2-gas doping without any activation process during MBE growth. LEDs and LDs were fabricated using the N2-gas doping method. The driving voltage of the LED was 3.8 V at the forward current of 20 mA. The threshold current density of the LD was about 1.4 M/cm? at77 K by pulsed operation. The oscillation of the ZnSe based LD fabricated without N-radical doping technique was achieved for the first time.

Reduction of p-ZnSe/p-GaAs non-ohmic barrier by inserting a GaN buffer layer

Abstract Nitrogen (N) radical irradiated GaAs was investigated by Auger analysis and reflection high-energy electron diffraction. N radical beam irradiation on GaAs causes an exchange of As atoms for N atoms, consequently forming a GaN layer onto the GaAs surface without a Ga source. No degradation of the ZnSe layers was observed when they were grown on GaAs substrates with GaN buffer layers. The current-voltage and capacitance-voltage characteristics of p-ZnSe/p-GaAs heterodiodes are examined. The necessary voltage for hole injection across the p-ZnSe/p-GaAs heterojunction is reduced to about half when a thin GaN buffer layer is inserted into the junction.

Dependence of SiC blue light-emitting diode efficiency on the p-type layer growth temperature

Dependence of SiC blue light-emitting diode (LED) efficiency on the p-type layer growth temperature in the liquid-phase epitaxial process was investigated. The external quantum efficiency of LEDs fabricated at a lower growth temperature was higher than that of those fabricated at a conventional growth temperature of 1720° C and maximized at a growth temperature of 1530° C. In this study, luminous intensity of 32 mcd was obtained at a forward current of 20 mA (λ P=467 nm).