Semiconductor properties of thin and thick film Ga2O3 ceramic layers

Abstract The semiconductor behavior of thin and thick film β Ga 2 O 3 layers is studied by measuring the resistivity as a function of oxygen partial pressure and temperature in the range up to 900°C. As for ZnO and SnO 2 a relatively high initial oxygen vacancy defect concentration has to be assumed for β Ga 2 O 3 . However, the conductivity is by many orders of magnitude lower and the activation energy by about 1 order of magnitude higher. With increasing temperature a change at about 810±50°C from a lower value of the activation energy E A (2)=1·6 ± 0·1 eV to a higher one E A (1)=2·4 ± 0·1 eV is observed at thin film ceramic layers thus leading to the assumption that oxygen cleavage in contact with the atmosphere is achieved in the upper range. Contrary to the band model which is convincingly founded for ZnO and SnO 2 in the literature, polaron hopping seems to be the more suitable model for analysis of the conductivity data of β Ga 2 O 3 . The lower value E A (2) is interpreted as the polaron hopping energy at approximately constant charge carrier concentration. On the other hand, in the high temperature range above T ch the charge carrier density is varying. However, at the applied measuring conditions, this variation remains below the initial oxygen vacancy defect concentration. Corresponding to formula I Ga III 2-2x Ga II 2x ′ O 3-x V { O ,x} and formula II Ga III 2-x Ga I x ″ O 3-x V { O ,x} two different structures for the oxygen vacancy defects in β Ga 2 O 3 are discussed. The measurements seem to confirm formula I. However, provided that there is an equilibrium between states corresponding to formula II and I, the assumption of double occupied Ga I states is also consistent with the experimental results.