Sadao Fujii

Visible InGaP/GaAsP Dual Wavelength Light Emitting Diodes

Visible dual wavelength light emitting diodes (LEDs) have been successfully fabricated growing lattice matched In0.3Ga0.7P on GaAs0.6P0.4 commercial epitaxial substrate on GaAs. InGaP and GaAsP homojunction LEDs have respective emission wavelength of 583 nm and 652 nm and cutoff frequencies of 8 MHz and 12 MHz.

LPE Growth of In1-xGaxAs1-yPy on GaAs0.7P0.3

Various In1-xGaxAs1-yPy epitaxial crystals with mirror-like surfaces were grown on GaAs0.7P0.3 substrates by LPE employing the two-phase-solution technique. The arsenic atomic fraction in the melt (XAsl) first increased with increasing XGal, but decreased above an XGal value of 0.03, while the solid As composition (1-y) increased monotonically. This somewhat strange behavior is explained as an increase in the As segregation coefficient with the increase in the As or Ga solid composition (x or 1-y), which results from the large value of the GaAs fusion temperature.

Meltback of GaAs0.6P0.4 Substrate in LPE Growth of InGaAsP

The meltback of a GaAs0.6P0.4 substrate was performed using an In melt containg Ga and As atoms. The experimental results and theoretical calculatios showed that the important factor in obtaining a good surface is to maintain the correct degree of unsaturation (-ΔT) of 5~30°C defined by the difference between the saturation temperature and the meltback temperature. Although no difference was found in the overgrown InGaAsP layer, an apparent improvement in the interfacial quality was found by etching back the substrate just before the growth.

A New Kind of Electroluminescent Devices Containing Ultrathin Polyimide Langmuir-Blodgett Films as Insulators

By utilizing ultrathin (100 and 200 A) polyimide Langmuir-Blodgett (PI LB) films as insulating layers and Ta2O5 as an electron injection layer, a new kind of multilayered thin film EL device having a low operating voltage of less than 100 V has been developed. Without Ta2O5, the threshold voltages were typically 50 V, but the slope of the luminance-voltage characteristic was not steep enough. By introducing two Ta2O5 layers, the luminance-voltage characteristics have been improved, and an operating voltage of 90 V has been achieved. This operating voltage is 50 V lower than that of a device which contains SiO2 instead of PI LB films.