Photoluminescence Investigations of AlGaN on GaN Epitaxial Films

Investigations on alloy potential fluctuations in AlxGa1−xN epilayers using optical characterizations

“…Accordingly, no phase separation is predicted in Al x Ga 1Ϫx N alloys. 10 However, in practice, the Al x Ga 1Ϫx N alloys with high Al contents also show the S-shaped PL shift as observed in In x Ga 1Ϫx N alloys or InGaN/GaN MQWs, and the S-shape behavior and Stokes shift have been explained in terms of the effects of localized states induced by alloy potential fluctuations in Al x Ga 1Ϫx N. [11][12][13][14][15][16] The amplitude of the potential fluctuation at the band edges caused by the alloy fluctuation is strongly correlated to the energy gap difference between the two semiconductors, 17 e.g., between GaN and AlN for Al x Ga 1Ϫx N (⌬E g ϭ2.8 eV). It is well known that the potential fluctuation plays an important role in determining the optical properties of alloy semiconductors including ZnS x Se 1Ϫx (xϽ0.18), 18 GaAs 1Ϫx P x , 19 CdS x Se 1Ϫx , 20,21 and Zn 1Ϫx Cd x Te.…”

“…Similar behavior has been reported previously for the temperature-dependent PL emission energy shift in In x Ga 1Ϫx N, InGaN/GaN MQWs, 8,9 Al x Ga 1Ϫx N, and pseudomorphic AlGaN/GaN heterostructures. [11][12][13][14][15][16][23][24][25][26][27] According to Lin et al, 29 the recombination of electron-hole ͑e-h͒ pair is considered to occur around the localized states. The e-h recombination pair increases with Al content in the Al x Ga 1Ϫx N epilayers due to strong alloy potential fluctuations.…”

“…Similar behavior has been reported previously for the In x Ga 1Ϫx N 29 and Al x Ga 1Ϫx N epilayers. 11,13,24,25 In the In x Ga 1Ϫx N-based light-emitting device structures, In alloy inhomogeneity, and/or quantum-dot-like In phase separation have been proposed as the origin of localized states, and temperature-induced blueshift attributed to band-tail states in the density of states has been observed. The theoretical calculation also predicts a high tendency of phase separation in the In-Ga-N alloy system, but not in Al x Ga 1Ϫx N epilayers.…”

“…However, Cho et al 23 showed that the Stokes shift between the PL emission peak energy and PLE absorption edge monotonically increases with varying Al contents. Comparing our results with previously reported one, [11][12][13][14][15][16][23][24][25][26][27] the large Stokes shift between PL emission and OA or PC strongly implies that the potential fluctuation does exist in Al x Ga 1Ϫx N epilayers. These results can be understood in terms of increase in the depth of localized states from the band edge of Al x Ga 1Ϫx N epilayers with large Al contents.…”

LP MOVPE growth and characterization of high Al content AlxGa1−xN epilayers

“…For these samples, an intense luminescence was observed in the UV region. The photoluminescence spectra are dominated by the donor bound exciton transition I 2 , which has been observed in the previous works [22][23][24][25]. The spectral position vary from 3.92 eV (x ¼ 0:25) to 4.78 (x ¼ 0:65).…”