Absorption Coefficient and Refractive Index of GaN, AIN and AlGaN Alloys
ABSTRACT The design of optoelectronic devices fabricated from III-nitride materials is aided by knowledge of the refractive index and absorption coefficient of these materials. The optical properties of GaN, AIN and A1GaN grown by MOVPE on sapphire substrates were investigated by means of transmittance and reflectance measurements. Thin (less than 0.5 μm) single crystal films were employed to insure that transmission measurements could be obtained well above the optical band gap. The influence of alloy broadening on the absorption edge was investigated by using a series of AlGaN alloy samples with a range of Al compositions. The optical absorption coefficient above the band gap was obtained for AIGaN having up to 38% Al composition. The refractive index below the band gap was determined for the same series of samples. These properties provide information critical to the optimal design of solar blind detectors or other optoelectronic devices.
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ABSTRACT: A high light-extraction efficiency was demonstrated in the flip-chip light-emitting diode (FCLED) with a textured sapphire substrate. The bottom side of a sapphire substrate was patterned using a dry etching process to increase the light-extraction efficiency. Light output power measurements indicated that the scattering of photons emitted in the active layer was considerably enhanced at the textured sapphire substrate resulting in an increase in the probability of escaping from the FCLED. The light-output power of the FCLED was increased by 40.2% for a 0.4-mum deep FCLED with a periodic distance of 13-mum mesh-type texture on the bottom side of the sapphire substrateIEEE Photonics Technology Letters 08/2006; · 2.04 Impact Factor
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ABSTRACT: We propose an artificial material, based on inclusions of low-dimensional quantum structures made of AlN/GaN semiconductor layers, in a similar setting to that of a quantum cascade amplifier. By a proper quantum-dispersion engineering, this metamaterial can be used as a nonmetallic guide of surface plasmon polaritons in the optical regime with the added benefit of amplification and modulation. Advanced dispersion engineering of this quantum system is detailed here and due to the rapid development of the epitaxial growth of such material, we expect that the full set of the required material parameters will be realized in the near future.Journal of Applied Physics 10/2008; · 2.21 Impact Factor
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ABSTRACT: Research into III-Nitride based avalanche photodiodes (APDs) is motivated by the need for high sensitivity ultraviolet (UV) detectors in numerous civilian and military applications. By designing III-Nitride photodetectors that utilize low-noise impact ionization high internal gain can be realized—GaN APDs operating in Geiger mode can achieve gains exceeding 1×10 7 . Thus with careful design, it becomes possible to count photons at the single photon level. In this paper we review the current state of the art in III-Nitride visible-blind APDs and discuss the critical design choices necessary to achieve high performance Geiger mode devices. Other major technical issues associated with the realization of visible-blind Geiger mode APDs are also discussed in detail and future prospects for improving upon the performance of these devices are outlined. The photon detection efficiency, dark count rate, and spectral response of or most recent Geiger-mode GaN APDs on free-standing GaN substrates are studied under low photon fluxes, with single photon detection capabilities being demonstrated. We also present our latest results regarding linear mode gain uniformity: the study of gain uniformity helps reveal the spatial origins of gain so that we can better understand the role of defects.Proc SPIE 08/2010; 1:847-467.