In this paper, we present the fabrication and Direct Current/high voltage characterizations of AlN-based thin and thick channel AlGaN/GaN heterostructures that are regrown by molecular beam epitaxy on AlN/sapphire. A very high lateral breakdown voltage above 10 kV was observed on the thin channel structure for large contact distances. Also, the buffer assessment revealed a remarkable breakdown field of 5 MV/cm for short contact distances, which is far beyond the theoretical limit of the GaN-based material system. The potential interest of the thin channel configuration in AlN-based high electron mobility transistors is confirmed by the much lower breakdown field that is obtained on the thick channel structure. Furthermore, fabricated transistors are fully functional on both structures with low leakage current, low on-resistance, and reduced temperature dependence as measured up to 300 °C. This is attributed to the ultra-wide bandgap AlN buffer, which is extremely promising for high power, high temperature future applications.

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.

AlN nucleation layers are the basement of GaN-on-Si structures grown for light-emitting diodes, high frequency telecommunication and power switching systems. In this context, our work aims to understand the origin of propagation losses in GaN-on-Si High Electron Mobility Transistors at microwaves frequencies, which are critical for efficient devices and circuits. AlN/Si structures are grown by Metalorganic Vapor Phase Epitaxy. Acceptor dopant in-diffusion (Al and Ga) into the Si substrate is studied by Secondary Ion Mass Spectroscopy and is mainly located in the first 200 nm beneath the interface. In this region, an acceptor concentration of a few 10 18 cm -3 is estimated from Capacitance–Voltage (C–V) measurements while the volume hole concentration of several 10 17 cm -3 is deduced from sheet resistance. Furthermore, the combination of scanning capacitance microscopy and scanning spreading resistance microscopy enables the 2D profiling of both the p -type conductive channel and the space charge region beneath the AlN/Si interface. We demonstrate that samples grown at lower temperature exhibit a p -doped conductive channel over a shallower depth which explains lower propagation losses in comparison with those synthesized at higher temperature. Our work highlights that this p -type channel can increase the propagation losses in the high-frequency devices but also that a memory effect associated with the previous sample growths with GaN can noticeably affect the physical properties in absence of proper reactor preparation. Hence, monitoring the acceptor dopant in-diffusion beneath the AlN/Si interface is crucial for achieving efficient GaN-on-Si microwave power devices.

Despite the fact that a lower growth temperature is generally considered as a drawback for achieving high crystal quality, the necessity to reduce the nucleation temperature of AlN on Silicon has permitted Molecular Beam Epitaxy (MBE) to demonstrate high performance for GaN transistors operating at high frequency. Compared to Metal‐Organic Vapor Phase Epitaxy (MOVPE), the control of the interface between the AlN nucleation layer and the substrate is easier and the reduced growth temperature allows to obtain a more electrically resistive interface while keeping good crystal quality. Moreover, it is shown that further reducing the growth temperature within the nucleation and stress mitigating layers has a noticeable impact on the lateral and vertical buffer leakage currents. At the same time the buffer of MBE grown HEMT structures exhibits low RF propagation losses (below 0.5 dB mm−1 up to 70 GHz). Also, results obtained with structures regrown by MOVPE on MBE AlN‐on‐Si templates confirm that the thermal budget is critical for the resistivity of AlN/Si. On the other hand, the insertion of a 1.5 μm thick Al0.05Ga0.95N layer within a 2 μm HEMT structure significantly improves the vertical breakdown voltage up to 740 V permitting to compare favorably with MOVPE epilayers with similar total thickness.