Preparation of Optoelectronic Devices Based on AlN/AlGaN Superlattices

Abstract

ABSTRACTWe present results on growth and fabrication experiments of AlN/AlGaN superlattices for ultraviolet (UV) optoelectronic devices. Superlattices with extremely short periods have been studied. The AlN “barrier” layers are 0.5 nm thick, and the AlxGa1-xN “wells” are 1.25 nm thick, with x ∼ 0.08. This combination gives an average AlN mole fraction of 0.63 across one full period. The superlattice periods, AlN mole fractions, and energy gaps are determined using TEM, X-ray diffraction, and optical reflectance. They are all consistent with each other. For device fabrication, p-i-n structures are grown doped with Si (n-type) and Mg (p-type). The acceptor activation energy of ∼ 0.2 eV is found. Mesa structures are plasma etched using chlorine chemistry. Etch rates of AlN are ∼ 1/3 those of GaN under identical circumstances. Etch rates of 250 nm/min are used for the device structures. A light emitting diode, with primary emission at 280 nm is reported, and a detector with sensitivity edge at 260 nm are reported.