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Phone: þ33 493 954 200, Fax: þ33 493 958 361In this paper, we investigate the reduction of thermal budgets associated with the growth of GaN high electron mobility transistor (HEMT) heterostructures. The reduction of such thermal budgets is desirable for the monolithic integration of GaN-HEMT with CMOS circuits, when the latter are fabricated first. Indeed, due to the elevated temperatures required for the growth of III-nitrides, the characteristics of the integrated CMOS devices may drift during the process. In order to determine in which extend the growth thermal budget could be reduced without penalty on the performances of GaN-HEMTs, different structures were grown by ammonia-molecular beam epitaxy (ammonia-MBE) with standard and reduced growth temperatures. The epitaxial structures were then compared with regards to their structural and electrical properties. The present work sets the limit for a potential trade-off between Si-CMOS and GaN-HEMTs degradation in a CMOS-first monolithic integration scenario.

We characterize a KOH-based ultraviolet (UV) photoassisted wet etching technique using K2S2O8 as the oxidizing agent. The solution provides a well-controlled etch rate and produces smooth high-quality etched surfaces with a minimal degradation in surface roughness as measured by atomic force microscopy. The evolution of the solution pH upon exposure to UV radiation is identified as key to obtaining smooth etched surfaces and a controlled etch rate: Unless steps are taken to maintain the pH above 12.0, the etch rate displays a sharp drop that coincides with a gross roughening of the etched surface. The applicability of the present technique is demonstrated by the fabrication of high-quality mesa-isolated AlGaN/GaN hetrostructure field-effect transistors. In addition, the etch presented here features a high selectivity to C-doped layers which should prove useful in the fabrication of AlGaN/GaN hetrostructure bipolar transistors. The method is well adapted to device processing applications because it does not require connection to the sample to an external electrochemical cell.