Electrical properties of β-Ga2O3 single crystals grown by the Czochralski method

Abstract

Electrical properties of nominally undoped β-Ga₂O₃ crystals grown by the Czochralski method from an iridium crucible under a carbon dioxide containing atmosphere were studied by temperature dependent conductivity and Hall effect measurements as well as deep level transient spectroscopy. All crystals were n-type with net donor concentrations between 6 × 10¹⁶ and 8 × 10¹⁷cm⁻³. The Hall mobility of electrons was on average 130 cm²/Vs at room temperature and attained a maximum of 500 cm²/Vs at 100 K. The donor ionization energy was dependent on the donor concentration. Extrapolation of this dependence to zero concentration yielded a value of about 36 meV for isolated donors agreeing well with the ionization energy derived from effective-mass theory. Three deep electron traps were found at 0.55, 0.74, and 1.04 eV below the conduction bandedge. The trap at E_C – 0.74 eV was detected in all samples with concentrations of 2 – 4 × 10¹⁶cm⁻³. This concentration is comparable to that of compensating acceptors we have to take into account for an explanation of the temperature dependent electron density. Therefore, under the assumption that the electron trap at E_C – 0.74 eV possesses acceptor character, this trap could be the dominating compensating acceptor in our crystals. Besides, a value of Φ_B = (1.1 ± 0.1) V was determined for the Schottky barrier height of Ni on the (100) surface of n-type β-Ga₂O₃.