Epitaxial growth and characterization of aluminum nitride and effects of ion irradiation on aluminum gallium nitride gallium nitride heterostructures

Abstract

Aluminum nitride (AlN), Gallium nitride (GaN) and its ternary alloy Aluminum Gallium Nitride (AlGaN) are the potential materials for ultraviolet emitters and detectors due to their direct wide band gap. The ultraviolet light emission from AlxGa1-xN can be tunable from 360 (GaN) to 200 (AlN) nm by varying the aluminum composition (x) from 0 to 100 %. The lack of native substrates forces the heteroepitaxial growth of AlN, GaN and AlGaN on sapphire (Al2O3) and silicon carbide (SiC) substrates. For cost reasons, c-plane sapphire is often used despite the large lattice mismatch and large difference in thermal expansion. AlN has been used as the buffer layer for AlGaN layer based deep ultraviolet (DUV) light emitting devices to accommodate the mismatches and reduce the dislocation density. AlN possesses excellent UV light transparency and excellent lattice match with high Al content AlGaN layers. In addition, AlN has high thermal conductivity (3.2 W cm-1 K-1) and high breakdown voltage (12 MV cm-1) essential for high-power and high temperature electronic devices. However, growth of AlN has many challenges due to the heteroepitaxy, high sticking coefficient of Aluminum (Al), parasitic reactions between Al and ammonia (NH3), etc. Despite these challenges, growth of AlN epilayers have been studied in detail with the AlN nucleation layers to improve the crystalline quality. On the other part, investigations on the radiation tolerance and defect resistance of AlGaN/GaN heterostructures upon swift heavy irradiation at room and low temperature have been carried out. Iv Growth of high temperature (HT) - AlN layers with nucleation layers have been performed using high temperature hydride vapor phase epitaxy (HT-HVPE) at 1200 and 1400 °C. The influence of growth temperature and HT-treatment on AlN nucleation layer (NL) morphology and thickness have been studied. It has been concluded that the rearrangement of the AlN-NL surface during HT-treatment at 1200 °C.