InGaAs/GaAsSb Heterostructures: Aluminum-Free Intersubband Devices
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1195-B11-01
InGaAs/GaAsSb Heterostructures: Aluminum-Free Intersubband Devices M. Nobile1, G. Strasser1,2, H. Detz1, E. Mujagic1, A. M. Andrews1, P. Klang1 and W. Schrenk1 1 Center for Micro-and Nanostructures and Institute for Solid State Electronics, Vienna University of Technology, Floragasse 7, 1040 Vienna, Austria 2 University at Buffalo, The State University of New York, Buffalo, NY 14260, USA ABSTRACT An experimental study on mid-infrared intersubband absorption in InGaAs/GaAsSb multiple quantum wells grown lattice-matched to InP substrates by molecular beam epitaxy is presented. Intersubband absorption in a broad wavelength region (5.8 - 11.6 µm) is observed in multiple quantum well samples with well widths ranging between 4.5 and 12 nm. A conduction band offset at the InGaAs/GaAsSb heterointerface of 360 meV gives an excellent agreement between the theoretically calculated ISB transition energies and the Fourier-transform infrared spectroscopy measurements over the whole range of well widths under investigation. Two kinds of intersubband devices based on the InGaAs/GaAsSb material system are presented: a quantum well infrared photodetector operating at a wavelength of 5.6µm and an aluminum-free quantum cascade laser. The presented quantum cascade laser emits at a wavelength of 11.3 µm, with a threshold current density of 1.7 kA/cm2 at 78 K. INTRODUCTION Intersubband (ISB) transitions in semiconductor quantum wells (QWs) are of paramount importance in optoelectronic devices, such as quantum cascade lasers (QCLs) [1] and quantum well infrared photodetectors (QWIPs) [2]. So far, the studies of ISB transitions in QWs have mainly dealt with III-V compounds. High power and high temperature performance QCLs have been demonstrated in InP based materials [3,4] as well as in the GaAs/AlGaAs system [5,6]. For the shorter wavelengths (2.75 - 4 µm), where a large conduction band offset is required, strain compensated InGaAs/AlGaAs, InGaAs/AlAsSb, InAs/AlSb based QCLs have been reported [7,8,9], while GaAs/AlGaAs and InGaAs/InAlAs structures have been shown for the generation of terahertz radiation (60 - 300 µm) [10,11]. However, all the above mentioned material systems contain a significant fraction of aluminum in the layers acting as barriers, where the effective mass of electrons is rather high. Since the electronic wave functions strongly penetrate the barriers in the active region of a QCL, a small electron effective mass in the barriers would be a benefit in terms of the optical matrix element [12]. Larger optical gain [13] and, therefore, improved laser performance are thus expected by using aluminum-free material combinations for the active region of a QCL. Besides the recent development of II-VI materials [14,15], a very promising candidate to this aim is the InGaAs/GaAsSb material system lattice-matched to InP. The InGaAs/GaAsSb heterostructure shows a type II alignment, with the InGaAs being the well for the electrons and the GaAsSb for the holes [16]. The conduction band offset (CBO) at the InGaAs/GaAsSb het
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