Luminescence Properties in Er,O-codoped GaAs Light-Emitting Devices with Double Excitation Mechanism
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1111-D01-02
Luminescence Properties in Er,O-codoped GaAs Light-Emitting Devices with Double Excitation Mechanism Y. Fujiwara, K. Fujii, A. Fujita, Y. Ota, Y. Ito, T. Kawasaki, K. Noguchi, T. Tsuji, A. Nishikawa and Y. Terai Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
ABSTRACT We fabricated a laser diode (LD) exhibiting a lasing from strained GaInAs quantum wells (QWs) embedded in Er,O-codoped GaAs (GaAs:Er,O) by organometallic vapor phase epitaxy (OMVPE). The lasing wavelength was designed to tune to the energy separation between the second excited states 4I11/2 and the ground state 4I15/2 of Er3+ ions. The threshold current for the lasing at room temperature was six times larger than that of a GaInAs QW-LD without Er doping, reflecting ultrafast carrier capture by an Er-related trap in GaAs:Er,O. The Er intensity revealed initially steep increase with injected current density in the region for spontaneous emission from the GaInAs QWs. In the stimulated QW emission region, the intensity continued to increase with the current density. INTRODUCTION Significant attention has been paid to rare-earth (RE) doped semiconductors as a promising new class of materials that emit light from the RE 4f shell by means of electrical injection. Er-doped semiconductors are particularly attractive because it can emit 1.5μm light. The wavelength is important for present silica-based optical communication. We have succeeded in atomically-controlled doping of Er to various III-V semiconductors such as GaAs and InP by organometallic vapor phase epitaxy (OMVPE) [1]. In Er,O-codoped GaAs (GaAs:Er,O), one kind of Er center was formed selectively as an Er atom located at the Ga sublattice with two adjacent O atoms (hereafter referred as Er-2O) together with two As atoms, resulting in drastic enhancement in intensity of Er-related luminescence due to intra-4f shell transitions of Er3+ ions [2,3]. We have fabricated GaInP/GaAs:Er,O/GaInP doubleheterostructure (DH) light-emitting diodes (LEDs), aiming at realizing the stimulated emission at the Er center under current injection. Radiant Er-2O electroluminescence has been successfully observed at around 1.54 μm at room temperature under forward bias [4]. Extremely large Er excitation cross section of 10-15 cm2 was obtained by current injection, which is five orders larger than optical excitation cross section in conventional Er-doped fiber amplifiers (10-20~10-21 cm2). For the improvement in the device performance, we have investigated quantitatively the mechanism of excitation and relaxation of Er ions by external excitation, and found that there is a characteristic ultrafast trapping process for nonequilibrium carriers in GaAs:Er,O [5]. The excitation mechanism of Er ions doped in the LEDs is as follows; current injection introduces a free electron and a free hole. If we assume a trap as a donor-like hole trap, the trap attracts an electron and creates an electron-hole pair. The electron-hole pa
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