Polarization of III-nitride blue and ultraviolet light-emitting diodes

Abstract

Polarization-resolved electroluminescence studies of III-nitride blue and ultraviolet (UV) light-emitting diodes (LEDs) were performed. The LEDs were fabricated on nitride materials grown by metalorganic chemical vapor deposition on sapphire substrates (0001). Transverse electric (TE) polarization dominates in the InGaN∕GaN quantum-well (QW) blue LEDs (λ′=458nm), whereas transverse magnetic (TM) polarization is dominant in the AlInGaN QW UV LEDs (λ=333nm). For the case of edge emission in blue LEDs, a ratio (r=I⊥∕I‖) of about 1.8:1 was observed between the EL intensities with polarization E⊥c (TE mode) and E‖c (TM mode), which corresponds to a degree of polarization ∼0.29. The UV LEDs exhibit a ratio r of about 1:2.3, corresponding to a degree of polarization ∼0.4. This is due to the fact that the degree of polarization of the bandedge emission of the AlxInyGa1−x−yN active layer changes with Al concentration. The low emission efficiency of nitride UV LEDs is partly related to this polarization property. Possible consequences and ways to enhance UV emitter performances related to this unique polarization property are discussed.

Extremely weak surface emission from (0001) c-plane AlGaN multiple quantum well structure in deep-ultraviolet spectral region

“…8 Experimental anisotropic optical polarization for the luminescence of the m-and c-plane InGaN, GaN, AlGaN, and AlN have been reported. [9][10][11][12][13][14][15][16][17][18] Recently, anisotropic optical polarization has also been discovered in the c-plane AlGaN multiple quantum well ͑MQW͒ laser. 19 In this letter, we report extremely weak surface emission and anisotropic emission from a ͑0001͒ c-plane Al x Ga 1−x N ͑x = 0.66-0.76͒ MQW in the spectral region from 228 to 240 nm under optical pumping, although a definite intensity of edge emission was still observed from the ͑1-100͒ cleaved m-plane facet.…”

Light-polarization characteristics of electroluminescence from InGaN∕GaN light-emitting diodes prepared on (112¯2)-plane GaN

“…3 The polarized EL from InGaN / GaN quantum-well ͑QW͒ LEDs fabricated on a nonpolar plane has been explained by the same origin. 12 On contrary, there are reports that no peak shift has been observed between two polarizations on GaN / AlGaN QW, 13 InGaN / GaN QW, 14 and AlInGaN QW. 14 Emission was assigned to transition from conduction band ͑C͒ to the topmost valence subband.…”

Anisotropy of Light Extraction Emission with High Polarization Ratio from GaN-based Photonic Crystal Light-Emitting Diodes

“…The observed polarization ratio has been reported to be as high as 7:1 for GaN/InGaN QWs [18]. For common GaN LED structures grown along the c axis, access to this polarized light can only be gained by measurements taken from the edge of the sample [19][20]. Several authors have reported polarized light emission for LED structures grown on nonpolar or semipolar GaN substrates [21][22].…”