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In this work, two series of AlGaN/GaN/AlN high electron mobility transistor (HEMT) heterostructures have been grown by molecular beam epitaxy on AlN bulk substrates. The effects of reduction in the GaN channel thickness as well as the AlGaN barrier thickness and composition on structural and electrical properties of the heterostructures have been studied. The material analysis involved high-resolution x-ray diffraction, atomic force microscopy, and cross-sectional transmission electron microscopy. In a first series of HEMT structures grown with an aluminum content of 30% in the AlGaN barrier, the channel downscaling results in a reduction in the GaN strain relaxation rate but at the expense of degradation in the mean crystal quality and in the electron mobility with a noticeable increase in the sheet resistance. An opposite trend is noticed for the three-terminal breakdown voltage of transistors, so that a trade-off is obtained for a 50 nm width GaN channel HEMT, which exhibits a sheet resistance of 1700 Ω/sq. with transistors demonstrating three-terminal breakdown voltage up to 1400 V for 40 μm gate to drain spacing with static on resistance Ron = 32 mΩ cm2. On the other hand, a second series of HEMT structures with high aluminum content AlGaN barriers and sub-10 nm GaN channels have been grown perfectly strained with high sheet carrier densities allowing to preserve sheet resistances in the range of 880–1050 Ω/sq. [ABSTRACT FROM AUTHOR]

In this work, the physical and the electrical properties of vertical GaN Schottky diodes were investigated. Cathodo-luminescence (CL), micro-Raman spectroscopy, SIMS, and current-voltage (I-V) measurements were performed to better understand the effects of physical parameters, for example structural defects and doping level inhomogeneity, on the diode electrical performances. Evidence of dislocations in the diode epilayer was spotted thanks to the CL measurements. Then, using 2D mappings of the E 2 h and A1 (LO) Raman modes, dislocations and other peculiar structural defects were observed. The I-V measurements of the diodes revealed a significant increase in the leakage current with applied reverse bias up to 200 V. The combination of physical and electrical characterization methods indicated that the electrical leakage in the reverse biased diodes seems more correlated with short range non-uniformities of the effective doping than with strain fluctuation induced by dislocations. [ABSTRACT FROM AUTHOR]

This paper reports comprehensive characterization of vertical GaN-on-GaN Schottky barrier diodes (SBDs) fabricated on free-standing GaN substrates. The GaN active layer properties are evaluated by atomic force microscopy (AFM), secondary-ion mass spectrometry (SIMS), micro-Raman spectroscopy, cathodoluminescence (CL), and deep-level transient Fourier spectroscopy (DLTFS). The GaN SBDs exhibit near-unity ideality factor (n = 1.1), promising Schottky barrier height (SBH) of Φ B = 0.82 eV, low turn-on voltage ∼0.56 V, leakage current density of J R < 5.5 × 10−6 Acm−2 at −100 V, breakdown voltage V BR < −200 V, and less interface state density (N SS < 5 × 1012 eV−1 cm−2) at the Ni/GaN Schottky contact. The forward and reverse current transport mechanisms of the SBD are identified by fitting analysis of measured J-V. Weak temperature dependence of Φ B and n is detected from I–V-T measurements. Similar traps at E C - 0.18 eV and E C - 0.56 are identified in the various SBDs from DLTFS, signifying that these traps are omnipresent defects in the epilayer. • Comprehensive characterizations are carried out for vertical GaN-on-GaN Schottky barrier diodes (SBDs). • Typical electrical characteristics of quasi-ideal vertical GaN-on-GaN SBDs are reported. • Various current transport mechanisms involved during forward and reverse characteristics of the SBD are identified. • The GaN active layer properties are evaluated by AFM, SIMS, micro-Raman spectroscopy, cathodoluminescence (CL). • Furthermore, traps in the GaN diodes are detected by deep level transient Fourier spectroscopy (DLTFS). [ABSTRACT FROM AUTHOR]