High-Quality Ge-Doped (010) $\beta$-Ga${}_2$O${}_3$ Homoepitaxial Films Grown by Low-pressure CVD: Structural, Electrical, and Schottky Diode Characteristics

Abstract

In this work, Ge-doped $\beta$-Ga${}_2$O${}_3$ homoepitaxial films were grown on native (010) $\beta$-Ga${}_2$O${}_3$ substrates using low-pressure chemical vapor deposition (LPCVD). Controlled $n$-type doping was achieved with room-temperature carrier concentrations ranging from $7.4\times 10^{17}$ to $2.57\times 10^{18}{\mathrm{cm}}^{-3}$ and corresponding electron mobilities of 105-62 cm${}^2$/V$\cdot$s. The films exhibited smooth surface morphology with RMS roughness values of 2.94-3.97 nm, while X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy confirmed phase-pure $\beta$-Ga${}_2$O${}_3$ with excellent crystalline quality and near-stoichiometric composition. Temperature-dependent Hall measurements on the film with a room-temperature carrier concentration of $7.4\times 10^{17}{\mathrm{cm}}^{-3}$ and mobility of 105 cm${}^2$/V$\cdot$s yielded a peak electron mobility of 234 cm${}^2$/V$\cdot$s at 116 K, while charge-neutrality and transport modeling revealed a dominant shallow donor level with an activation energy of 14 meV, confirming efficient electrical activation of Ge donors. Vertical Ni/$\beta$-Ga${}_2$O${}_3$ Schottky barrier diodes fabricated using the Ge-doped drift layer exhibited good rectifying behavior with a turn-on voltage of 0.74 V, an ideality factor of 1.32, a Schottky barrier height of 1.02 eV, and a specific on-resistance of 2.49 m$\Omega \cdot$cm${}^2$. Capacitance-voltage measurements yielded a net donor concentration of $7.7\times 10^{17}{\mathrm{cm}}^{-3}$ and a Schottky barrier height of 1.13 eV, in good agreement with Hall and current-voltage measurements. These results demonstrate that LPCVD enables controllable Ge doping while maintaining high structural and electronic quality, establishing LPCVD-grown Ge-doped $\beta$-Ga${}_2$O${}_3$ as a promising platform for future high-voltage power electronic devices.