High Spatial Resolution Energy Dispersive X-ray Spectroscopy and Atom Probe Tomography study of Indium segregation in N-polar InGaN Quantum Wells

N-polar grown III-nitrides are very interesting materials for the fabrication of heterostructures devices such as transistors, photodetectors, solar cells or optoelectronic devices. In GaN/(In,Ga)N/GaN heterostructures with thin (In,Ga)N layers, polarization engineering allows to achieve interband tunneling. Thereby the tunneling probability is proportional to the indium concentration in the InGaN layers. Indium incorporation is higher for N-polar InGaN films than for the typically grown Ga-polar ones. N-polar III nitride films are often grown on misoriented substrates enabling the growth of smooth, high quality layers [1]. The crystal misorientation leads to the formation of surface steps, and misorientation angles of 4°-5° can result in up to 3-4 unit cell high steps. The growth of N-polar InGaN films is further complicated by the necessary reduced growth temperatures and the required absence of hydrogen in the growth ambient. In quantum well structures, however, hydrogen, which acts as surfactant and promotes the growth of smooth layers, can be introduced during GaN barrier growth, allowing the deposition of thick multiple quantum well (MQW) stacks. Ga-polar InGaN films have been extensively studied and are known for their local fluctuations in the indium composition [2]. Not much is known about the uniformity of N-polar InGaN layers.