III‐Nitrides semiconductor compounds for microwave devices

This paper reports on the LP-MOCVD growth optimisation of GaAlN/GaN heterostructures grown on sapphire and silicon carbide substrates for HEMT applications, and on the device performances obtained with these structures. The devices performances related to the GaAlN/GaN HEMT structures grown on sapphire and silicon carbide have confirmed the high potentiality of GaN and related alloys for high power microwave transistors. Load-Pull measurements performed at 2 GHz on devices related to GaAlN/GaN/Al 2 O 3 HEMT structures, have shown a remarkably high output power density (4.4 W/mm) and absolute power level (3.2 W for 1 mm devices). These power level results for devices on sapphire substrates measured on wafer, are well in agreement with the international state of the art. Devices related to GaAlN/GaN/SiC HEMT structures have been measured at 10 GHz using a load pull system. They exhibited a CW output power in excess of 6.2 W/mm for a gate length of 0.25 μm and an absolute CW power level of 60 W (22 mm development). On the other hand, the GaAlN/InGaN/GaN double heterostructure, in which the channel layer is made of InGaN instead of GaN, is expected to significantly enhance device performance due to a stronger carrier confinement and a higher two-dimensional electron gas (2DEG) density at the interface in comparison with an GaAlN/GaN single heterostructure. Simin et al. have demonstrated GaInN channel devices with RF output powers as high as 4.3 W/mm in CW mode [2]. Recently, HEMT devices based on InAlN/GaN lattice-matched heterostructures exhibiting very promising RF performances have been reported (4.1 W/mm at 2 GHz) [3]. These different heterostructures used for HEMT devices are compared to the conventional GaAlN/GaN heterostructure in term of device results.