Proposal of a novel BeZnSeTe quaternary for II‐VI middle range visible light emitting devices on InP substrates

Abstract

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.

Investigation of p‐contact layers for BeZnSeTe/MgZnCdSe optical devices on InP substrates

“…Then, a MgSe(4ML)/BeZnTe(6ML) SL n-barrier layer (50 nm), a BeZnTe(1ML)/ZnSeTe(10ML) SL active layer (30 nm), a MgSe(4ML)/BeZnTe(6ML) SL p-barrier layer (9 nm), a MgSe(4ML)/BeZnTe(6ML) SL pcladding layer (600 nm), and finally a ZnTe or ZnSeTe contact layers (30 nm) were sequentially grown at 300 °C. Here, the graded SL was introduced to relax the conduction band hetero barrier in electron injection from the ncladding to the n-barrier layers [11]. In this device, the graded SL was composed of 20-pair MgSe(2ML)/ ZnCdSe(3ML), 18-pair MgSe(2ML)/ZnCdSe(2ML) and 12-pair MgSe(2ML)/ZnCdSe(1ML) SLs from the ncladding layer side.…”

Long life operations over 5000 hours of BeZnSeTe/MgZnCdSe visible light emitting diodes on InP substrates

“…ZnCl 2 and a radio frequency (RF) nitrogen source were used for the n-and p-type doping. Detailed structure and growth condition are described elsewhere [5]. The Au-Ge alloy and Au metals were evaporated on the substrate backside and the p-contact layers to make ohmic contacts, respectively.…”

“…The type-II junction functions as a hetero barrier for hole injections from the p-cladding into the active layers, resulting in causing type-II emissions and/or non-radiative recombinations at the hetero interface. In order to solve the problem, we have proposed BeZnSeTe quaternaries to apply for the active layer [5]. In the replacing of the ZnCdSe active layers with BeZnSeTe, the valence band edge rises, which makes the type-II valence band hetero barrier decrease or disappear.…”

Investigation of p-side contact layers for II–VI compound semiconductor optical devices fabricated on InP substrates by MBE

“…II-VI compound semiconductors such as ZnCdSe, BeZnTe, and BeZnSeTe on InP substrates are very attractive for use in visible-toinfrared optical devices [1][2][3][4][5][6][7][8][9]. Using these materials, we are developing green and yellow laser diodes (LDs) and light-emitting diodes (LEDs) [3][4][5][6][7][8][9].…”