Thermally stimulated current (TSC) spectroscopy and temperature–dependent dark current (DC) measurements have been applied to study traps and photoinduced persistent surface conduction in two hydrothermally grown bulk ZnO samples, as-grown, and annealed at 600 °C in N2 ambient for 30 min, respectively. The as-grown sample had a room-temperature (RT) resistivity of 1.6×103 Ω cm, mobility of 2.1×102 cm2/V s, and carrier concentration of 1.8×1013 cm−3, while the annealed sample was highly resistive, with RT resistivity of 3.6×106 Ω cm, mobility of 4.4 cm2/V s, and carrier concentration of 3.9×1011 cm−3. The as-grown sample showed strong conduction at low temperatures, which has been shown to be due to near-surface carriers in other studies. The annealed sample did not demonstrate this phenomenon. The dominant trap in the as-grown sample had an activation energy of 0.16 eV, was strongest near the surface, and is possibly related to VZn. In the annealed sample, however, the dominant trap had an activation energy of 0.22 eV, was of bulk nature, and is tentatively assigned to LiZn. After several routine TSC measurements, the DC for the as-grown sample increased by more than one order of magnitude at low temperatures (T<180 >K), while for the annealed sample, the DC increased by a factor of 2 at high temperatures (T>200 K). These effects are generated by the TSC trap-filling illumination and can persist for many days under vacuum. At RT, the DC in the annealed sample returns to its equilibrium state if the sample is vented to air.
& Look, D. C.
(2008). Effects of Annealing in N(2) Ambient on Traps and Persistent Conduction in Hydrothermally Grown ZnO. Journal of Applied Physics, 103 (7), 73714.