Realization of extremely high internal quantum efficiencies from AlGaN/AlN quantum wells
Abstract
AlGaN/AlN quantum wells (QWs) with internal quantum efficiencies (IQEs) as high as 69% emitting at 247 nm at room temperature were realized by metalorganic vapor phase epitaxy. The extremely high IQEs were achieved upon examining the impact of the growth parameters such as source−supply sequence and growth temperature (Tg) on the QW quality. With the same emission wavelength (λ), QWs fabricated by continuous source−supply method have higher IQEs compared to QWs grown by modified migration enhanced epitaxy (MMEE) method due to its higher Tg, thus exhibiting superior crystalline quality with minimal point defects or impurities. Moreover, the alternating source-supply sequence of NH3 source in MMEE promotes Ga evaporation and consequently decreases Ga incorporation, thus obtaining QWs with shorter λ compared to QWs fabricated by the continuous method. Furthermore, regardless of the growth method, λ increases initially with IQE then decreases after reaching a maximum with longer λ. The increase is attributed to enhanced quantum confinement and carrier localization, whereas the decrease is due to lattice relaxation.
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