Mid-infrared intersubband absorption in GaN/AlGaN superlattices on Si(111) templates

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Effect of doping on the mid-infrared intersubband absorption in GaN/AlGaN superlattices grown on Si(111) templates

International audienceWe report on the effect of Si doping on the mid-infrared intersubband absorption in GaN/AlGaN superlattices. For increasing doping levels, interband luminescence displays a blueshift and a broadening of the band edge caused by the screening of the internal electric field and band-filling effects. The intersubband absorption energy is mainly governed by many-body effects like exchange interaction and depolarization shift, which increase the e(1)-e(2) subband separation. The ISB blueshift induced by many-body effects can be more than 50% of the e(1)-e(2) transition energy

Terahertz intersubband absorption in GaN/AlGaN step quantum wells

International audienceWe demonstrate terahertz intersubband absorptions at frequencies of 2.1 THz (lambda approximate to 143 mu m) and 4.2 THz (lambda approximate to 70 mu m) in nitride-based semiconductor quantum wells. The structures consist of a 3 nm thick GaN well, an Al(0.05)Ga(0.95)N step barrier, and a 3 nm thick Al(0.1)Ga(0.9)N barrier. The absorption is detected at 4.7 K. The structure design has been optimized to approach a flat-band potential in the wells to allow for an intersubband absorption in the terahertz frequency range and to maximize the optical dipole moments. (C) 2010 American Institute of Physics. [doi:10.1063/1.3515423

Interband and intersubband optical characterization of semipolar (112¯2)-oriented GaN/AlN multiple-quantum-well structures

International audienceWe report on semipolar GaN/AlN multiple-quantum-well structures grown on m-plane sapphire by plasma-assisted molecular-beam epitaxy. Optical investigation confirms a significant reduction in the quantum-confined Stark effect, in agreement with theoretical calculations, which predict an internal electric field between 0.6 and −0.55 MV/cm in the quantum wells, depending on the strain state. With respect to polar materials, the reduction in the internal electric field results in a substantial redshift of the intersubband energy

Growth of intersubband GaN/AlGaN heterostructures

GaN/AlN multiple quantum wells (MQWs), designed for intersubband (ISB) absorption in the telecommunication range, are grown by molecular beam epitaxy. We demonstrate that the use of both AlN template and optimized growth temperature allows to reach ISB transition energy in the telecom range, i.e. above 0.8 eV (lambda = 1.55 mu m). Absorption spectra exhibit narrow linewidth (< 50 meV) with a relative energy broadening of 8%. An electro-optical modulator based on electron tunnelling in coupled QWs is then fabricated. A modulation bandwidth of 2 GHz at -3 dB cut off frequency is achieved for 15x15 mu m(2) mesas. We show that the modulation rate is limited by the device geometry rather than by the material quality, which makes this technology a good candidate for THz regime

Polar and Semipolar III-Nitrides for long wavelength intersubband devices

International audienceExtending the intersubband transitions in III-nitride nanostructures from near-infrared to longer wavelengths might have significant consequences for critical applications like imaging, remote sensing and mine detection. In this work, we analyze the potential of polar and semipolar AlGaN/GaN technologies for this relevant spectral range