【International Papers】Enhancing the electron mobility in Si-doped (010)β-Ga₂O₃ films with low-temperature buffer layers

      Recently, the University of California, Santa Barbara, and the University of Utah published an article in the scientific journal APL Materials titled Enhancing the Electron Mobility in Si dropped (010) β- Paper article on Ga₂O₃ films with low performance buffer layers.

      We demonstrate a new substrate cleaning and buffer growth scheme in β-Ga₂O₃ epitaxial thin films using metal–organic vapor phase epitaxy (MOVPE). For the channel structure, a low-temperature (LT, 600 °C) un-doped Ga₂O₃ buffer was grown, followed by a transition layer to a high-temperature (HT, 810 °C) Si-doped Ga₂O₃ channel layers without growth interruption. The (010) Ga₂O₃ Fe-doped substrate cleaning uses solvent cleaning, followed by additional hydrofluoric acid (49% in water) treatment for 30 min before the epilayer growth. This step is shown to compensate the parasitic Si channel at the epilayer–substrate interface that originates from the substrate polishing process or contamination from the ambient. From secondary ion mass spectroscopy (SIMS) analysis, the Si peak atomic density at the substrate interface is found to be several times lower than the Fe atomic density in the substrate—indicating full compensation. The elimination of the parasitic electron channel at the epi–substrate interface was also verified by electrical (capacitance–voltage profiling) measurements. In the LT-grown (600 °C) buffer layers, it is seen that the Fe forward decay tail from the substrate is very sharp, with a decay rate of ∼9 nm/dec. X-ray off-axis rocking curve ω-scans show very narrow full width at half maximum (FWHM) values, similar to the as-received substrates. These channels show record high electron mobility in the range of 196–85 cm²/V⋅s in unintentionally doped and Si-doped films in the doping range of 2 × 10¹⁶–1 × 10²⁰ cm⁻³. Si delta-doped channels were also grown utilizing this substrate cleaning and the hybrid LT buffers. Record high electron Hall mobility of 110 cm²/V⋅s was measured for sheet charge density of 9.2 × 10¹² cm⁻². This substrate cleaning, combined with the LT buffer scheme, shows the potential of designing Si-doped β-Ga₂O₃ channels with exceptional transport properties for high-performance Ga₂O₃-based electron devices.

Fig. Atomic force microscopy scans (1 × 1 μm²) for the (010) Fe-doped Ga₂O₃ substrate before and after the substrate cleaning process. (a) As-received substrate (b) after 30 min of HF (49%) treatment and an in situ O₂ annealing for 10 min at 600 °C.

Fig. 2D cross-sectional schematic of the channel structure used for the uniformly and intentionally Si-doped films for doping range of 10¹⁷–10²⁰ cm⁻³. It shows the substrate preparation, LT buffer, and the HT Si-doped channel stack used. (GR = growth rate, HT = high-temperature, LT = low-temperature).