Search

Fabrication of low-RF loss GaN-on-Si high electron mobility transistor stacks is critical to enable competitive front-end-modules for 5G and 6G applications. The main contribution to RF losses is the interface between the III-N layer and the HR Si wafer, more specifically the AlN/Si interface. At this interface, a parasitic surface conduction layer exists in Si, which decreases the substrate effective resistivity sensed by overlying circuitry below the nominal Si resistivity. However, a clear understanding of this interface with control of the parasitic channel is lacking. In this Letter, a detailed physical and electrical description of metalorganic chemical vapor deposition-grown AlN/Si structures is presented. The presence of a SiCxNy interfacial layer is revealed, and its importance for RF losses is shown. Through C–V and I–V characterization, an increase in the C concentration of this interfacial layer is linked to the formation of negative charge at the AlN/Si interface, which counteracts the positive charge present in the 0-predose limit. The variation of the TMAl predose is shown to allow precise tuning of the C composition and, consequently, the resulting interface charge. Notably, a linear relationship between the predose and the net interface charge is observed and confirmed by the fabrication of an AlN/Si sample with close to zero net charge. In addition, a higher Dit (∼ 2 × 10 12 c m − 2 ) for such compensated samples is observed and can contribute to low-RF loss. An exceptionally high effective resistivity of above 8 kΩ cm is achieved, corresponding to an RF loss below 0.3 dB/mm at 10 GHz. [ABSTRACT FROM AUTHOR]

We report a comprehensive analysis of the leakage current mechanism in ion implantation isolation (I/I/I) regions of GaN high electron mobility transistors. We applied a three-step high-energy low-dose N I/I/I to AlGaN/AlN/GaN heterostructures. High-quality isolation is achieved with isolation sheet resistances Rsh in the range of 1013–1015 Ω/sq. The analysis of isolated heterostructures with varied AlGaN or AlN thicknesses indicates common electron leakage paths at the surface of GaN. The electrostatics of the leakage path is determined by an interplay between the high densities of defects created by I/I/I, the net sheet polarization charges between III-nitrides, and the AlGaN surface states. We find that the activation energy of Rsh positively correlates with the energy level of the leakage path. The energy band diagram of the isolation region is constructed by correlating the activation energies of Rsh with the heteerostructure electrostatics. Moreover, our study makes a novel method to estimate the net active defect density caused by I/I/I: net active defect densities of ∼2 × 1019 and ∼2 × 1018 cm−3 are extracted in the GaN and AlGaN layers, respectively. [ABSTRACT FROM AUTHOR]

Boltzmann relations are widely used in semiconductor physics to express the charge-carrier densities as a function of the Fermi level and temperature. However, these simple exponential relations only apply to sharp band edges of the conduction and valence bands. In this article, we present a generalization of the Boltzmann relations accounting for exponential band tails. To this end, the required Fermi–Dirac integral is first recast as a Gauss hypergeometric function followed by a suitable transformation of that special function and a zeroth-order series expansion using the hypergeometric series. This results in simple relations for the electron and hole densities that each involve two exponentials. One exponential depends on the temperature and the other one on the band-tail parameter. The proposed relations tend to the Boltzmann relations if the band-tail parameters tend to zero. This work is timely for the modeling of semiconductor devices at cryogenic temperatures for large-scale quantum computing. [ABSTRACT FROM AUTHOR]

High-temperature processing steps are frequently used in manufacture of AlGaN/(AlN/)GaN high electron mobility transistors (HEMTs). The thermal budgets drive Al diffusion into the GaN channel, increase alloy disorder scattering (ADS) of the two-dimensional-electron-gas (2DEG), and degrade the 2DEG mobility. By correlating the ADS to device thermal budget, we propose an analytical model to calculate the ADS limited mobility as a function of Al diffusion lengths (LD,Al) in AlGaN/(AlN/)GaN HEMTs. The simulation indicates that the ADS is a significant mobility degradation mechanism whose scattering rate increases with the 2DEG density and the LD,Al. The findings explain the generally observed trends in the literature that the 2DEG mobility and sheet resistances of GaN heterostructures degrade with increased thermal budgets, especially after >900 °C processing. [ABSTRACT FROM AUTHOR]