Temperature‐dependent electrical characterization of exfoliated β‐Ga2O3 micro flakes

Among the transparent semiconducting oxides β‐Ga2O3 is of high interest because of its wide‐band gap of 4.8 eV and the corresponding transparency from deep ultraviolet to near infrared spectra. Here, we report on the preparation, structural and temperature‐dependent electrical characterization of thin β‐Ga2O3 micro flakes. β‐Ga2O3 single crystals are grown using Czochralski technique. Micro flakes are prepared via exfoliation technique in the thickness range from 2.4 to 300 nm. The samples are characterized using confocal microscopy, atomic force microscopy, scanning electron microscopy and transmission electron microscopy. Transport investigations of β‐Ga2O3 micro flakes are performed in the temperature range from 30 to 300 K. The electrical parameters of flakes with thicknesses larger than 100 nm correspond to those of the source bulk single crystals of highest purity and mobility. The electrical resistivity at room temperature amounts to ρ(293 K) = (1.5 ± 0.5) Ω cm. The temperature‐dependent resistivity has a minimum at T = 130 K of about ρ(130 K) ∼ 1 Ω cm. This finds an explanation in the maximum of the bulk mobility. From the increase of ρ(T) between 130 and 300 K we determine an activation energy of Ea = (−10.5 ± 0.4) meV. For temperatures below 50 K ρ(T) increases indicating a freeze‐out of charge carriers. The non‐alloyed Ti/β‐Ga2O3 metal‐semiconductor contact resistance grows inverse with temperature as expected for thermionic emission. At room temperature the Ti/β‐Ga2O3 contact resistance is comparable to the resistance of the flake for low current densities of j < 100 A cm−2. However, at high current densities j > 100 A cm−2 this contact resistance is negligible.