Luminescence Properties of GaN/In x Ga 1−x N/In y Ga 1−y N Double Graded Structures (Zigzag Quantum Wells)

We have designed graded InGaN quantum well (QW) structures with the In composition increasing then decreasing in a zigzag pattern. Through polarization doping, this naturally creates a p–n junction. Separate structures are designed by varying the maximum In composition but maintaining a constant QW thickness. This is both in order to test the limits of the molecular beam epitaxy growth control in terms of the deposition source ramping rates and to determine the limits of the maximum In composition within a narrow QW. The composition, x, of InxGa1−xN is varied for all structures starting from a minimum of xmin = ∼ 3%, and increasing to different maximum compositions, xmax, then finally decreasing back to ∼ 3%. The samples are characterized for their structural and luminescent properties. The results of the photoluminescence studies on samples with xmax ranging up to 35% demonstrate broadband emission covering wavelengths between 380 nm and 700 nm. Additionally, although the general emission of structures with increasing xmax shifts to lower energy, the observed luminescence is comprised of several individual peaks which are currently being investigated as to their particular origin.