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

We demonstrate a new substrate cleaning and buffer growth scheme in beta-Ga2O3 epitaxial thin films using metal-organic vapor phase epitaxy (MOVPE). For the channel structure, a low-temperature (LT, 600 & DEG;C) un-doped Ga2O3 buffer was grown, followed by a transition layer to a high-temperature (HT, 810 & DEG;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 & DEG;C) buffer layers, it is seen that the Fe forward decay tail from the substrate is very sharp, with a decay rate of & SIM;9 nm/dec. X-ray off-axis rocking curve omega-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 cm(2)/V.s in unintentionally doped and Si-doped films in the doping range of 2 x 10(16)-1 x 10(20) 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 cm(2)/V.s was measured for sheet charge density of 9.2 x 10(12) cm(-2). This substrate cleaning, combined with the LT buffer scheme, shows the potential of designing Si-doped beta-Ga2O3 channels with exceptional transport properties for high-performance Ga2O3-based electron devices.

Automated summary

We demonstrate a new substrate cleaning and buffer growth scheme in beta-Ga2O3 epitaxial thin films using MOVPE. By growing a low-temperature un-doped Ga2O3 buffer followed by a transition layer to high-temperature Si-doped Ga2O3 channel layers, continuous growth of the channel structure was achieved. The parasitic Si channel at the epilayer-substrate interface was effectively compensated through solvent cleaning and hydrofluoric acid treatment. This substrate cleaning combined with the LT buffer scheme shows the potential for designing Si-doped beta-Ga2O3 channels with exceptional transport properties.