High sensitivity of photoluminescence‐ excitation spectroscopy for probing effects of plasma‐induced surface damages on carrier transport in AlxGa1–xN/GaN heterostructures

We demonstrate that photoluminescence-excitation (PLE) spectroscopy is applicable to probe effects of the surface damages on the carrier transport in AlxGa1–xN/GaN heterostructures by systematically characterizing as-grown and plasma-exposed samples. The characterization of the surface morphology with atomic force microscopy clarifies that the plasma exposure modifies the atomic steps and pits on the AlxGa1–xN surface. The PLE spectrum of the as-grown sample measured at the energy of the photoluminescence from the GaN layer shows a step rising from the AlxGa1–xN fundamental transition energy, which reflects the photogenerated-carrier injection from the AlxGa1–xN layer to the GaN layer, while the rising step disappears in the plasma-exposed sample. In contrast, the reflectance spectra are the same in the two samples; namely, the excitonic transition is hardly changed. Thus, it is concluded that PLE spectroscopy is highly sensitive to probe the carrier-transport characteristics in the AlxGa1–xN/GaN heterostructure. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)