Absorption coefficient and refractive index of GaN, AIN and AlGaN alloys

MRS Online Proceeding Library 12/1997; 537. DOI: 10.1557/PROC-537-G5.2

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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Available from: John Muth, May 07, 2015
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    • "Using transfer-matrix-approach (TMA) simulation [15], the center reflectivity of the Rb was calculated to be 87.1% at 330 nm with a stop bandwidth of 16.8 nm, and the center reflectivity of the Rf was 39.3%, both of which are basically in accordance with the test results of reflectance spectrum for 20-pair and 3-pair DBR samples. According to the relation of reflectivity and the thickness of absorption layer [1]), the total thickness of the GaN absorption layer must be set to 33.2 nm to get the maximum of QE, where is the thickness of the absorption layers and cm is the absorption coefficient of GaN at 330 nm [16]. However, for exact etching to the p-GaN layer, the absorption layer should be thicker, so here we designed it to be 80 nm (20 nm i-GaN and 60 nm p-GaN). "
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    ABSTRACT: AlGaN-based resonant-cavity-enhanced (RCE) p-i-n photodetectors (PDs) for operating at the wavelength of 330 nm were designed and fabricated. A 20.5-pair AlN/Al<sub>0.3</sub>Ga<sub>0.7</sub>N distributed Bragg reflector (DBR) was used as the back mirror and a 3-pair AlN/Al<sub>0.3</sub>Ga<sub>0.7</sub>N DBR as the front one. In the cavity is a p-GaN/i-GaN/n-Al<sub>0.3</sub>Ga<sub>0.7</sub>N structure. The optical absorption of the RCE PD structure is at most 59.8% deduced from reflectance measurement. Selectively enhanced by the cavity effect, a response peak of 0.128 A/W at 330 nm with a half-peak breadth of 5.5 nm was obtained under zero bias. The peak wavelength shifted 15 nm with the incident angle of light increasing from 0deg to 60deg.
    IEEE Journal of Quantum Electronics 07/2009; 45(6-45):575 - 578. DOI:10.1109/JQE.2009.2013146 · 1.89 Impact Factor
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    • ". Measured quantum efficiency of GaN samples Fig. 4. Calculated 1/e attenuation depth for GaN on sapphire substrates, opaque mode, showing the [Muth et al 7 1999] and relative (1/e) -1 as a function of evolution of sample processing techniques on the QE. wavelength, showing the behavior at the band gap. "
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    ABSTRACT: The nitride-III semiconductors, in particular GaN (band gap energy 3.5 eV), AlN (band gap 6.2 eV) and their alloys AlxGa1-xN are attractive as UV photo-convertors with applications as photocathodes for position sensitive detector systems. These can "fill the gap" in the 150-400nm wavelength regime between alkali halide photocathodes (4000Å, mutlialkali & GaAs). Currently CsTe photocathodes have fairly low efficiency (Fig. 1) in the 100nm to 300nm regime are sensitive to contamination and have no tolerance to gas exposure. We have prepared and measured a number of GaN photocathodes in opaque and semitransparent modes, achieving >50% quantum efficiency in opaque mode and ~35% in semitransparent mode (Fig. 2). The GaN photocathodes are stable over periods of >1 year and are robust enough to be re-activated many times. The cutoff wavelength is sharp, with a rapid decline in quantum efficiency at ~380-400nm. Application of GaN photocathodes in imaging devices should be feasible in the near future. Further performance improvements are also expected as GaN fabrication and processing techniques are refined.
    Proceedings of SPIE - The International Society for Optical Engineering 01/2003; DOI:10.1117/12.510429 · 0.20 Impact Factor
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    ABSTRACT: Ce mémoire est consacré à l'étude du couplage lumière-matière dans des structures à base de GaN (semiconducteur à bande interdite directe). L'objectif de ce travail est la mise en évidence expérimentale du couplage fort exciton-photon dans des microcavités à base de GaN. Des difficultés liées à l'élaboration des nitrures nous ont contraint à effectuer deux études préliminaires : tout d'abord, la détermination des indices de réfraction d'AlN, GaN et AlGaN par ellipsométrie spectroscopique et par réflectivité, puis la caractérisation de miroirs de Bragg AlN/GaN et AlN/AlGaN. A partir des résultats obtenus, nous avons imaginé puis effectué le design de plusieurs structures de microcavités pour lesquelles le couplage fort lumière-matière était atteint théoriquement. Les microcavités ont ensuite été élaborées par épitaxie sous jets moléculaires sur substrat de silicium et nous les avons caractérisées par spectroscopie optique : réflectivité et photoluminescence à basse température, en fonction de l'angle d'incidence et de la position. Les expériences de réflectivité résolues en angle nous ont permis de mettre en évidence pour la première fois le régime de couplage fort dans une microcavité à base de GaN. La structure étudiée est une microcavité massive à base de GaN encastrée entre 4 alternances de couches diélectriques SiO2/Si3N4 formant le miroir haut et le substrat de silicium jouant le rôle du miroir bas. Le régime de couplage fort atteint dans cette structure est caractérisé par un dédoublement de Rabi de 31 meV persistant à une température de 77K, mais ne subsistant pas à température ambiante, à cause des élargissements induits par l'augmentation de la température. Finalement, nous avons proposé des microcavités massives ou à puits quantiques permettant théoriquement l'observation du régime de couplage fort à température ambiante. Ainsi, des dispositifs tels que le laser à polaritons, laser à très faible seuil, pourrait être envisagé.
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