Schottky barrier height of Ni to β -(Al x Ga 1−x ) ₂ O ₃ with different compositions grown by plasma-assisted molecular beam epitaxy

Coherent β -(Al x Ga 1−x ) 2 O 3 films ( x = 0, 0.038, 0.084, 0.164) were grown successfully on a Sn-doped β -Ga 2 O 3 (010) substrate using plasma-assisted molecular beam epitaxy. Atom probe tomography, transmission electron microscopy, and high resolution x-ray diffraction were used to verify the alloy composition and high quality of the films. Schottky diodes were then fabricated using Ni as the Schottky metal. Capacitance–voltage measurements revealed a very low (<7 × 10 15 cm −3 ) free charge density in the nominally undoped films. The barrier height and ideality factor were estimated by current–voltage ( I–V ) measurements performed at temperatures varying from 300 K to 500 K on the Schottky diodes. These measurements revealed that the apparent Schottky barrier height could have similar values for different compositions of β -(Al x Ga 1−x ) 2 O 3 . We believe this is attributed to the lateral fluctuation in the alloy’s composition. This results in a lateral variation in the barrier height. Therefore, the average Schottky barrier height extracted from I–V measurements could be similar for β -(Al x Ga 1−x ) 2 O 3 films with different compositions.