Effects of a cap layer on built-in electric fields of AlxGa1-xN/GaN heterostructures non-destructively probed by Franz-Keldysh oscillationsH. Takeuchi, Y. Yamamoto, Y. Kamo, T. Oku and M. NakayamaEur. Phys. J. B, 52 3 (2006) 311-314DOI: https://doi.org/10.1140/epjb/e2006-00302-y