Photoluminescence linearly polarized

LINEARLY POLARIZED PHOTOLUMINESCENCE FROM GaN QUANTUM DOTS EMBEDDED IN AIN MATRIX... 

We report on polarization sensitive microphotoluminescence studies of wurtzite type GaN/AlN quantum dots grown on (0001) sapphire substrates by molecular beam epitaxy. Typical linearly polarization degree of photoluminescence is about 0.06. Photoluminescence intensity of some particular samples decreases over time under continuous-wave excitation on a timescale of minutes. Emission of such samples is linearly polarized with polarization degree of about 0.15. Possible reasons of the observed behavior are discussed. 

The PL spectra of the sample 417 at orthogonal directions of polarization are shown on Fig. 2. It is seen, that its photoluminescence is linearly polarized with the polarization degree P = 0.15, which was defined as... 

Linearly polarized photoluminescence from GaN quantum dots embedded in AIN matrix. 

The in-plane polarization anisotropy can be enhanced by anisotropic strain. This can be achieved by choosing a nonpolar orientation with an appropriate substrate. In the extreme case of M-plane GaN on liAl02, the degree of linear polarization can be increased to its maximum value of one for all three transitions between the three uppermost valence bands (VBs) and the conduction band (CB), corresponding to complete linear polarization for all three transitions. This optical anisotropy can be observed in transmission (absorption) and reflection, as well as photoluminescence (PL) and photoreflectance (PR) spectroscopy. It can therefore be used for polarization filtering, polarization-sensitive photodetectors (PSPDs), and polarized light emitters. For anisotropically strained C-plane GaN films on (1120) sapphire, the in-plane polarization properties have been previously reported in Refs. 1-3. 

Fig. 7.9 Left) Linearly polarized absorption and photoluminescence spectra (excitation wavelength 370 nm) of an OLED containing a 73 nm thick F(MB)10F(EH)2 film, with an inset showing the electron diffraction pattern. (Right) Device structure and polarized EL spectra of an OLED containing a 35 nm thick F(MB)10F(EH)2 film (From Culligan et al. [41])...

Potyrailo and Leach (2006) used the same approach. They evaluated the response of the luminescence from CdSe nanoparticles incorporated into a polymer film to the exposure of polar and nonpolar vapors. It was found that different size nanocrystals provided individual photoluminescence response patterns when the sensor film was exposed to methanol and toluene. Ma et al. (2009) have shown that under optimal conditions the PL intensity of CdTe QDs incorporated in poly(dimethyldiallylammonium chloride) decreased linearly with the increase of formaldehyde concentration in the range 5-500 ppb. The detection limit for formaldehyde was 1 ppb. Other examples of QD-based gas sensors are presented in Table 5.1. 

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