12.4 GaN-Based Polarizing LEDs
281
Fig. 12.20 Diffraction of the photon crystal to the wave vector [45]
further separates due to the larger tension stress with the increase of the wavelength
in the InGaN. Then, the probability of CB-|X> recombination was enhanced due to
further reduction of CB-|Z> transition matrix. The theory was confirmed by Brinkley
in 2011 [42]. They produced Blue LEDs on m-plane GaN, and the higher polarization
ratio was obtained with the increase of In composition.
The m-plane GaN-based LEDs are of the higher polarization ratio. This is one of
the very promising methods. Unfortunately, it is difficult to grow the high-qualify
material. It is not suitable for commercialize on a large scale. At first, m-GaN
substrates are costly. The photonic crystal with the size of 100 nm is a challenge.
Therefore, the process can’t be realized at present. Secondly, the quality of the material should be improved at the wavelength in green band. Unfortunately, it is very
difficult due to high dislocation density. Of course, A-plane GaN and semi-polar
GaN show the similar properties as discussed above.
12.4.4 The Edge-Emitting Polarized LEDs
The edge-emitting polarization was found by J. Shakya in blue and ultraviolet LEDs
in 2002 [48]. The polarization ratio was up to 1.8–2.3, which is related with the
light confinement of the multiple quantum wells because the polarization light with
low-order mode was more easily escaped from the sides. Chuanyu Jia in Peking
University found that the polarization ratio decreases from 3.2 to 1.9 due to the
competition between the quantum dot and the quantum well with rich-In zone when
the wavelength of InGaN-based LEDs changed from 395 to 455 nm [49]. A 460 nm
wavelength of LED was prepared by Schubert In 2007, and the polarization ratio
was up to 7 as shown in Fig. 12.21. The side-emitting polarization LEDs was manufactured using conventional process with simple and low-cost advantages. However,
the light extraction efficiency is low because only side-emitting light is polarized.
This is a small portion of total light.
281
Fig. 12.20 Diffraction of the photon crystal to the wave vector [45]
further separates due to the larger tension stress with the increase of the wavelength
in the InGaN. Then, the probability of CB-|X> recombination was enhanced due to
further reduction of CB-|Z> transition matrix. The theory was confirmed by Brinkley
in 2011 [42]. They produced Blue LEDs on m-plane GaN, and the higher polarization
ratio was obtained with the increase of In composition.
The m-plane GaN-based LEDs are of the higher polarization ratio. This is one of
the very promising methods. Unfortunately, it is difficult to grow the high-qualify
material. It is not suitable for commercialize on a large scale. At first, m-GaN
substrates are costly. The photonic crystal with the size of 100 nm is a challenge.
Therefore, the process can’t be realized at present. Secondly, the quality of the material should be improved at the wavelength in green band. Unfortunately, it is very
difficult due to high dislocation density. Of course, A-plane GaN and semi-polar
GaN show the similar properties as discussed above.
12.4.4 The Edge-Emitting Polarized LEDs
The edge-emitting polarization was found by J. Shakya in blue and ultraviolet LEDs
in 2002 [48]. The polarization ratio was up to 1.8–2.3, which is related with the
light confinement of the multiple quantum wells because the polarization light with
low-order mode was more easily escaped from the sides. Chuanyu Jia in Peking
University found that the polarization ratio decreases from 3.2 to 1.9 due to the
competition between the quantum dot and the quantum well with rich-In zone when
the wavelength of InGaN-based LEDs changed from 395 to 455 nm [49]. A 460 nm
wavelength of LED was prepared by Schubert In 2007, and the polarization ratio
was up to 7 as shown in Fig. 12.21. The side-emitting polarization LEDs was manufactured using conventional process with simple and low-cost advantages. However,
the light extraction efficiency is low because only side-emitting light is polarized.
This is a small portion of total light.