Spontaneous polarization effects in GaN/AlxGa1-xN quantum wells

We observe in GaN/AlxGa1-xN quantum wells with varying aluminum concentrati on strong electric fields whose amplitudes are significantly larger than th ose observed before in comparable structures fabricated at higher growth te mperatures. We show that the measured fields are clearly stronger than what is expected based on piezoelectric effects alone, which constitutes a dire ct experimental proof of the existence of important spontaneous polarizatio n effects in the GaN/AlxGa1-xN heterostructure system.