Editors' Choice Communication—A (001) β-Ga₂O₃MOSFET with +2.9 V Threshold Voltage and HfO₂Gate Dielectric

Abstract

An MOS transistor fabricated on (001) β-Ga 2 O 3 exfoliated from a commercial (−201) β-Ga 2 O 3 substrate is reported. A maximum drain current of 11.1 mA/mm was measured, and a non-destructive breakdown was reached around 80 V in the off state. Threshold voltage of +2.9 V was extracted at 0.1 V drain bias, and peak transconductance of 0.18 mS/mm was measured at V DS = 1 V, corresponding to a field effect mobility of 0.17 cm 2 /Vs. Hall effect and electron spin resonance data suggested that electron conductivity was due primarily to O vacancy donors (V O + ) with an estimated density of 2. The single-crystal monoclinic (β) phase of Ga 2 O 3 is an advantageous material for high-power, high-temperature electronic device applications due to its high energy gap (4.8-4.9 eV) and high breakdown field (8 MV/cm), yielding a nearly ten-fold higher Baliga figure of merit than that of 4H-SiC (BFOM Ga 2 O 3 = 3444, BFOM 4H-SiC = 300).1 Commercially available β-Ga 2 O 3 substrates enable the epitaxial growth of low defect density epitaxial β-Ga 2 O 3 by a number of methods, including chemical vapor deposition, hydride vapor phase epitaxy (HVPE), and molecular beam epitaxy (MBE), among others.2-6 Schottky barrier diodes (SBDs) based on Ga 2 O 3 have exhibited very low turn on voltage and reverse leakage current, suggesting that unintentionally doped Ga 2 O 3 has extremely low generation/recombination rates and thus a high photoconductive gain.7 Advances in doping control have enabled exceptional early reports of metal-and metal-insulatorgated field effect transistors (MOSFETs). Wong et al. demonstrated a field-plated β-Ga 2 O 3 MOSFET with a breakdown voltage of over 750 V using a Si-implanted channel.8 Most recently, Green and coworkers have reported a Ga 2 O 3 MOSFET with a Sn-doped channel and a 0.6 μm gate-drain spacing to operate at 200 V drain bias, experimentally demonstrating gate-drain fields in excess of 3 MV/cm. 9This excellent progress has positioned Ga 2 O 3 as a viable candidate for next generation material for power applications. However, no demonstration of normally-off operation, a key requirement for fail-safe operation of power switches, has been achieved or proposed to-date.From a practical perspective, development of Ga 2 O 3 transistors has been limited by the availability of device-quality epitaxial films. For this reason, early reports have exploited the relatively large a-plane lattice constant of β-Ga 2 O 3 (1.2 nm) in order to mechanically exfoliate thin films from the (001) plane of a substrate using the scotch tape method to fabricate back-gated devices. 10,11 We employed a similar method to transfer a thin (∼300 nm) Ga 2 O 3 flake onto a SiO 2 /Si substrate, 12 and performed a standard top-side insulated-gate process to fabricate a three-terminal device. We also utilized a high-k HfO 2 gate dielectric process, as only SiO 2 and Al 2 O 3 have been reported to-date. 13,14Experimental A thin sliver of Ga 2 O 3 was cleaved along the (001) face of an on-axis (−201), non-intentionally n-type doped (∼3 ×...

Towards High‐Mobility Heteroepitaxial β‐Ga2O3 on Sapphire − Dependence on The Substrate Off‐Axis Angle

“…The conduction mechanism is dominated by donor band conduction at low temperatures resulting in weak increase in carrier concentration. Optical phonon scattering at high temperatures and ionized impurity scattering at low temperatures also limit the electron mobility in these thin films . The thin films with the higher carrier concentrations exhibited a similar trend for the temperature dependence of the carrier, mobility and resistivity.…”

High-Performance Depletion/Enhancement-ode $\beta$ -Ga2O3 on Insulator (GOOI) Field-Effect Transistors With Record Drain Currents of 600/450 mA/mm

“…3(a) presents the I D -V DS output characteristics of an E-mode GOOI FET with L G = 1.3 μm and channel thickness of 79 nm. A record high I DMAX = 450 mA/mm is obtained, which is more than one order of magnitude higher than any other E-mode MOSFETs [14], [15]. Similar to D-mode device, the R on , R SH and R C of E-mode device are extracted to be 20 ·mm, 14.1 k / , and 0.95 ·mm, respectively.…”

Ultrawide‐Bandgap Semiconductors: Research Opportunities and Challenges

“…Measured electron mobilities are in the 100-200 cm 2 V −1 s −1 range at room temperature, up to about 500 cm 2 V −1 s −1 in the 100-200 K range for low-doped bulk material, [158,159] and up to even 5000 cm 2 V −1 s −1 at 80 K in high-quality HVPE-grown epitaxial layers. [160] As illustrated in Figure 8, mobility in Ga 2 O 3 appears to be limited by optical phonon scattering at high temperature and ionized impurity scattering at low temperature.…”