Field and temperature-dependent electronic transport parameters of amorphous and polycrystalline GaSe thin films

DC electrical conduction studies on vacuum evaporated thin films of GaSe in both the amorphous and polycrystalline states using the Al-GaSe-Al sandwich structure has been performed. Under low electric field (∼2.2x105 V cm-1) condition, in amorphous films in the temperature range 250-310 K and in polycrystalline films in the temperature range 190-250 K the variable-range hopping conduction of Mott's type is identified. For the same field, the Seto's model of thermionic emission for polycrystalline film (280-370 K) perfectly suits. The amorphous and polycrystalline GaSe thin films have localized states density values of N(EF)=1.686x1017 and 1.257x1015 cm-3 eV-1, respectively. The activation energies are found to be 0.317 and 0.087 eV, respectively for these two forms of material. The analysis of I-V characteristics, based on space charge limited currents measurements, confirms the exponential decrease of density of states from the conduction band edge towards the Fermi level for both the amorphous and polycrystalline films