AlN/GaN heterostructures grown by metal organic vapor phase epitaxy with in situ Si3N4 passivation

AlN/GaN heterostructures are very attractive because their theoretical two-dimensional electron gas (2DEG) density may exceed 5×1013/cm2 [1]. However, there are very few reports on AlN/GaN heterostructures grown by MOVPE. In this work, we show that good quality AlN layers can be grown on GaN at a relatively low growth temperature when TMIn is added to the carrier gas flow as a surfactant. Analysis by RBS revealed that at a growth temperature of 900°C or higher no Indium is actually incorporated. Various thicknesses of AlN are grown, from 2 to 8nm. Finally, 2–3nm in situ Si3N4 is deposited in order to protect the AlN surface and thus prevent stress relaxation. AFM revealed that the root-mean-square (RMS) roughness in a 1×1μm2 area is 0.25nm. When the AlN thickness reaches 8nm, the sheet resistance can be as low as 186±3Ω/□. Van der Pauw–Hall measurements show that the electron density is about 2.5×1013/cm2 with electron mobility exceeding 1140cm2/Vs when extra 50nm PECVD SiN is deposited.