Semiconductor properties of thin and thick film Ga2O3 ceramic layers

The semiconductor behavior of thin and thick film beta Ga2O3 layers is stud ied by measuring the resistivity as a function of oxygen partial pressure a nd temperature in the range up to 900 degrees C. As for ZnO and SnO2 a rela tively high initial oxygen vacancy defect concentration has to be assumed f or beta Ga2O3. However, the conductivity is by many orders of magnitude low er and the activation energy by about I order of magnitude higher. With inc reasing temperature a change at about 810 +/- 50 degrees C from a lower val ue 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 th e assumption that oxygen cleavage in contact with the atmosphere is achieve d in the upper range. Contrary to the band model which is convincingly foun ded for ZnO and SnO2 in the literature, polaron hopping seems to be the mor e suitable model for analysis of the conductivity data of beta Ga2O3. The l ower value E-A(2) is interpreted as the polaron hopping energy at approxima tely 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 ini tial oxygen vacancy defect concentration. Corresponding to formula I (Ga2-2 xGa2xO3-xV(O)-Ga-III-O-II double over dot ,x) and formula II (Ga2-xGaxI)-Ga -III" O3-xV(O double over dot ,x) two different structures for the oxygen v acancy defects in beta Ga2O3 are discussed. The measurements seem to confir m formula I. However, provided that there is an equilibrium between states corresponding to formula II and I, the assumption of double occupied Ga-I s tares is also consistent with the experimental results. (C) 1998 Elsevier S cience Limited. All rights reserved.