Asymmetric Hybrid Al(Ga)SbAs/InAs/Cd(Mg)Se Heterostructures for Mid-IR LEDS and Lasers
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Asymmetric Hybrid Al(Ga)SbAs/InAs/Cd(Mg)Se Heterostructures for Mid-IR LEDS and Lasers S.V. Ivanov, V.A. Kaygorodov, V.A. Solov’ev, E.V. Ivanov, K.D. Moiseev, S.V. Sorokin, B.Ya. Meltzer, A.N. Semenov, M.P. Mikhailova, Yu.P. Yakovlev and P.S. Kop'ev Ioffe Physico-Technical Institute of RAS, Politekhnicheskaya 26, St. Petersburg 194021, Russia ABSTRACT A hybrid double heterostructure with large asymmetric band offsets, combining AlAsSb/InAs (as a III-V part) and CdMgSe/CdSe (as a II-VI part), has been proposed as a basic element of a mid-infrared laser structure design. The p-i-n diode structure has been successfully grown by molecular beam epitaxy (MBE) and exhibited an intense long-wavelength electroluminescence at 3.12 µm (300K). A II-VI MBE growth initiation with a thin ZnTe buffer layer prior to the CdMgSe deposition results in a dramatic reduction of defect density originating at the II-VI/III-V interface, as demonstrated by transmission electron microscopy. A less than 10 times reduction of electroluminescence intensity from 77 to 300K indicates an efficient carrier confinement in the InAs active layer due to high potential barriers in conduction and valence bands, estimated as ∆EC = 1.28 eV and ∆EV ~ 1.6 eV. An increase in the pumping current results in a super-linear raising the EL intensity. The type of band line up at the coherent InAs/Cd1-xMgxSe interface is discussed for 0≤x≤0.2, using experimental data and theoretical estimations within a model-solid theory. INTRODUCTION Fabrication of room temperature cw semiconductor laser diodes for the 3-5 µm spectral range is still a big challenge. A hole leakage from an active region of pure III-V laser structures due to the particular valence band line up of InAs usually used in the active region may hamper the achievement of a low threshold current and a high output power [1]. To solve the problem of efficient hole confinement in InAs, taking a benefit of type I and type II band alignment, we have proposed a hybrid III-V/II-VI double heterostructure with large asymmetric band offsets in conduction (AlAsSb/InAs) and valence (InAs/CdMgSe) bands, as a basic element of a new mid-IR laser structure design [2]. In this case AlAsSb and CdMgSe form a strong type II heterojunction, while InAs layer interfaces are of type I, that leads, on the one hand, to high optical gain and quantum efficiency like in conventional type I double heterostructure lasers and, on the other hand, to significant suppression of both electron and hole leakage from the active region. The important feature of the proposed structure that it can be grown pseudomorphical as a whole because both AlAsSb and CdMgSe are lattice-matched to the InAs at appropriate ternary alloy compositions. An improvement of the structural quality is shown to be achieved by growing a thin ZnTe buffer layer at the III-V/II-VI interface. EXPERIMENTAL DETAILES The III-V part of the hybrid structures was grown by molecular beam epitaxy (MBE) in a Riber 32 chamber on a p+-InAs (100) substrate at temperature TS=480°C. It consi
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