Electrical characteristics of palladium Schottky contacts to hydrogen peroxide treated hydrothermally grown ZnO

Abstract

The formation of Schottky barrier contacts to hydrogen peroxide treated ZnO has been investigated. Low resistivity hydrothermally grown single crystal ZnO wafers of n-type were used. Pd contacts deposited on organic solvent cleaned O face (0001¯) showed Ohmic behavior, while on the H2O2 treated O face up to nine orders of magnitude in rectification of the current was obtained for biases of −2 and +2V. Concurrently, the surface roughness increases from 1.0±0.5 up to 2.0±0.5nm due to the H2O2 treatment. A majority of the contacs deposited were stable or improved their performance by annealing in air at 200°C for 30min. However, the contacts both before and after the annealing exhibited ideality factors of at least ∼1.8 at +0.5V suggesting that the current transport cannot be described as purely thermionic. Finally, results of capacitance versus voltage and capacitance versus temperature measurements are discussed and show a dominant electron state at ∼0.32eV below the conduction band edge.

Influence of annealing atmosphere on formation of electrically-active defects in rutile TiO2

“…This treatment is commonly used for the preparation of Schottky diodes on ZnO and has proven to lead to highly rectifying diodes. 49 Between 10 and 15 Pd contacts with a thickness in the range of $150-200 nm were deposited onto the samples via electron beam evaporation, using a Si shadow mask with pad areas of 0.7 Â 10 À3 to 4.2 Â 10 À3 cm 2 . Eutectic InGa was used as Ohmic back contact.…”

Origin of conductive surface layer in annealed ZnO

“…For example, surface conductivity may affect the properties of gas sensors, 4 and also devices that incorporate Schottky barriers. 5 Recently, we have shown that nearly all commercially available ZnO wafers ͑that we have examined͒ have a conductive surface layer ͑CSL͒ that totally dominates the sample conductance at low temperatures and sometimes strongly influences the conductance even at room temperature. 6 Thus, to accurately characterize the total electrical properties of a wafer, it is necessary to separate the bulk and surface contributions.…”

Zn- and O-face polarity effects at ZnO surfaces and metal interfaces

“…1 Metal/ZnO interfaces are essential to all ZnO electronic device applications, yet fabricating high quality and thermally stable rectifying and Ohmic ZnO contacts remains a challenge and their electronic properties have only recently been explored in detail. [2][3][4][5][6][7] Metals on semiconductors seldom obey the Schottky-Mott theory, i.e., their Schottky barrier heights are not proportional to their work functions. 8 Previous ZnO surface studies revealed the importance of surface adsorbates, near-interface native defects, and thermally induced interface chemical interactions at metal/ZnO contacts.…”