A novel BeZnSeTe quaternary has been proposed for active layers of II-VI visible light emitting devices on InP substrates. BeZnSeTe, which lattice parameters were matched to InP, were grown on InP substrates by molecular beam epitaxy (MBE). The Be composition was changed from 0.11 to 0.35. The photoluminescence (PL) spectra of these samples at 15 K showed single peak emissions with wavelengths from 487 to 506 nm without any deep level emission. From the reflectivity and PL spectra at 15 K, the Γ-Γ direct and Γ-X indirect bandgaps of BeZnSeTe were evaluated, and it is shown that the crossover point from direct to indirect is around Be composition of 0.3. Applying the BeZnSeTe for the active layer, visible light emitting diodes (LEDs) were fabricated on InP substrates by MBE, resulting in yellow light single peak emissions around 575 nm at room temperature. [1,2]. In this structure, however, hole injection into the active layer was obstructed by the valence-band discontinuity between the active and p-cladding layers because of their type-II band lineup, which deteriorates the device characteristics.In this paper, novel BeZnSeTe quaternaries are proposed to solve this problem. By applying BeZnSeTe for active layers instead of ZnCdSe, the valence band top shifts toward the higher electron energy, by which the valence band discontinuity of concern can be decreased or disappeared. As the bandgap energy of BeZnSeTe can be controlled in the range from 2.1 to 2.7 eV keeping lattice-matching to InP, so yellow-to-blue color light emissions are expected. Meanwhile the incorpolation of BeSe and BeTe into the crystal contributes to enhancing the lattice-hardness, which may be effective to lengthening the device lifetime. In the experiment, BeZnSeTe quaternaries were grown on InP substrates by molecular beam epitaxy (MBE). The photoluminescence (PL) and light reflectivity spectra of BeZnSeTe were measured at 15 K to evaluate the Γ-Γ direct and Γ-X indirect bandgaps. By that, the direct-to-indirect crossover is discussed. Visible light emitting diodes (LEDs) with BeZnSeTe active layers were fabricated, observing the yellow light single-peak emission around 575 nm at room temperature.
Middle-range visible light emitting diodes (LEDs) were fabricated using MgZnCdSe, BeZnTe, and BeZnSeTe [I-VI materials grown on InP substrates by molecular beam epitaxy. By changing the elemental compositions of BeZnSeTe active layers, yellow-green-to-orange emissions were obtained at 542, 575, and 594 nm in wavelength. A long lifetime CW operation of the 575nm yellow LED for more than 3000 hours has been achieved. The injection current density was 130 Ncm'. This result shows higher reliability of the BeZnSeTe LEDs against the precedent ZnCdSehIgZnSSe-based 11-VI LEDs on GaAs substrates.
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