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In this paper, we report on the fabrication of a normally-off Al(Ga)N/GaN high electron mobility transistor with selective area sublimation under vacuum of the p type doped GaN cap layer. This soft method makes it possible to avoid damages otherwise induced by post processing with reactive ion etching techniques. The GaN evaporation selectivity is demonstrated on AlN as well as on AlGaN barrier layers. Furthermore, by properly choosing the AlGaN barrier thickness and composition it is possible to co-integrate a normally-off with a normally-on device on the same substrate. Finally, a local area regrowth of AlGaN can complement this process to increase the maximum drain current in the transistors. [ABSTRACT FROM AUTHOR]

We report on the influence of a capping layer on the photoluminescence properties of self-assembled GaN quantum dots grown on an Al0.5Ga0.5N template. Self-assembled GaN quantum dots show a large quantum confined Stark shift and long carrier recombination time due to strong built-in spontaneous and piezoelectric polarization fields. Nevertheless, owing to strong carrier localization and suppressed nonradiative processes, these quantum dots have a high-quantum efficiency even at room temperature. Here, we show that the capping thickness has an important role on the optical properties of the GaN quantum dots. The radiative and nonradiative recombination processes of quantum dots are strongly affected by adjusting the capping thickness, and the GaN quantum dots with 12 monolayers-thick Al0.5Ga0.5N capping layer show a remarkably high internal quantum efficiency of more than 80% at room temperature. We also studied photoluminescence quenching and enhancement for surface (uncapped) quantum dots caused by photoadsorption and photodesorption of oxygen. [ABSTRACT FROM AUTHOR]