Buffer-less Gallium Nitride High Electron Mobility Heterostructures on Silicon

Abstract

Thick metamorphic buffers are considered indispensable for III-V semiconductor heteroepitaxy on large lattice and thermal-expansion mismatched silicon substrates. However, III-nitride buffers in conventional GaN-on-Si high electron mobility transistors (HEMT) impose a substantial thermal resistance, deteriorating device efficiency and lifetime by throttling heat extraction. To circumvent this, a systematic methodology for the direct growth of GaN after the AlN nucleation layer on 6-inch silicon substrates is demonstrated using metal-organic vapor phase epitaxy (MOVPE). Crucial growth-stress modulation to prevent epilayer cracking is achieved even without buffers, and threading dislocation densities comparable to those in buffered structures are realised. The buffer-less design yields a GaN-to-substrate thermal resistance of (11±4) m2KGW-1, an order of magnitude reduction over conventional GaN-on-Si and one of the lowest on any non-native substrate. As-grown AlGaN/AlN/GaN heterojunctions on this template show a high-quality 2D electron gas (2DEG) whose room-temperature Halleffect mobility exceeds 2000 cm2/(V·s), rivalling the best-reported values. As further validation, the low-temperature magnetoresistance of this 2DEG shows clear Shubnikov-de-Haas oscillations, a quantum lifetime > 0.180 ps, and tell-tale signatures of spin-splitting. These results could establish a new platform for III-nitrides, potentially enhancing the energy efficiency of power transistors and enabling fundamental investigations into electron dynamics in quasi-2D wide-bandgap systems.