We report an experimental determination of the internal polarization field in GaInN/GaN quantum wells, due to piezoelectric and spontaneous polarization, utilizing the quantum confined Stark effect, with fields as large as 3.1 MV/cm at 22% In. From its dependence on quantum well composition and strain, we find that the total field in GaInN is a linear combination of polarization charges from GaN and InN. The piezoelectric constants d31 for GaN and InN derived from our data are 1.05±0.05 pm/V and 3.7±0.5 pm/V, in fair agreement with theoretical data.
Using a high-resolution low-temperature spectroscopic scanning near-field optical microscope we observe highly localized high-energy emissions from highly efficient Ga x In 1−x N / GaN quantum wells. These sharp emissions about 300-400 meV above the main quantum well luminescence are characteristic for highefficiency structures and originate from the immediate vicinity of threading dislocations. Thus, areas of increased bandgap surrounding the defects appear to exist only in high-efficiency structures, which act as barriers prohibiting carriers from recombining nonradiatively at the defects.
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