1.37 - 2.90 Micron Intersubband Transitions in GaN/AlN Superlattices
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1.37 - 2.90 Micron Intersubband Transitions in GaN/AlN Superlattices Eric Anthony DeCuir, Jr. 1, Emil Fred1, Omar Manasreh1, Jinqiao Xie2, Hadis Morkoc2, Esther Baumann3, and Daniel Hofstetter3 1 Department of Electrical Engineering, University of Arkansas, 3217 Bell Engineering Center, Fayetteville, AR, 72701 2 Department of Electrical Engineering and Physics Department, Virginia Commonwealth University, Richmond, VA, 23284 3 Institute of Physics, University of Neuchatel, A.-L Breguet, Neuchatel, 2000, Switzerland
ABSTRACT Intersubband transitions in the spectral range of 1.37-2.90 µm are observed in molecular beam epitaxy grown Si-doped GaN/AlN multiple quantum wells using a Fourier-transform spectroscopy technique. A blue shift in the peak position of the intersubband transition is observed as the well width is decreased. A sample with a well width in the order of 2.4 nm exhibited the presence of three bound states in the GaN well. The bound state energy levels are calculated using a transfer matrix method. An electrochemical capacitance voltage technique is used to obtain the three dimensional carrier concentrations in these samples which further enable the calculation of the Fermi energy level position. Devices fabricated from these GaN/AlN quantum wells are found to operate in the photovoltaic mode. INTRODUCTION In recent years, progress in III-nitride epitaxial growth extends the applications of this class of materials from the ultraviolet range into the near infrared spectral region of 1.3–1.5 µm [1-5]. The ability to engineer quantum well structures consisting of Al1-xGaxN and GaN over a wide spectral range is made possible by the considerable conduction band offset between the two binaries AlN and GaN (~1.70 eV). In theory, the magnitude of this band offset enables the tuning of intersubband transition wavelengths from 0.70 µm and longer. However, in the past, dislocation densities [6,7] inherited from largely mismatched substrates and doping control in III-nitride materials [8] has hindered the production of high quality materials and slowed the improvement of device performance. However, intense research in understanding growth kinetics of nitride materials has enabled steady progress in the growth and fabrication of detectors based on the intersubband transitions in GaN/AlN-based systems [1-3, 7-10]. In this study, a variety of buffer layer schemes using both AlN and GaN is employed in the growth of the several GaN/AlN superlattice samples in which the intersubband transition wavelengths approach 1.30µm. Devices are fabricated from an GaN/AlN structure and measured at either 15K or 300K. Good agreement is obtained between calculated energy levels and experimental absorption measurements. In addition, three-dimensional carrier concentrations collected by an electrochemical capacitance-voltage (ECV) technique are obtained, which also enable the calculation of the Fermi energy level position.
EXPERIMENTS Short period Si-doped GaN/AlN superlattices are grown on c-plane sapphire substrates us
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