Physico-Chemical nanomaterials science

Electrical properties of p-CuCoO2/n-Si heterojunction
Koziarskyi D.P., Koziarskyi I.P., Maistruk E.V.
Yuriy Fedkovych Chernivtsi National University, 2 Kotsubynsky st., 58002 Chernivtsi, Ukraine. 
E-mail: d.koziarskyi@chnu.edu.ua

Delafossite (CuCoO2) oxides have been widely testified to be used in the fields of translucent conductive oxides (TCO), solar cell devices, photocatalysis, and other optoelectronic devices as p-type semi-conductive materials [1]. The development of p-type TCO will give us possibilities that cannot be used with n-type materials alone, such as transparent p-n heterojunction, diodes, transistors [2]. 
Thin CuCoO2 films (~ 200 nm thick) were obtained by RF magnetron sputtering on glass substrates and on plane-parallel n-Si plates. A stoichiometric mixture of CuO and CoO2 was used to make the target. Substrate temperature t°S = 380 °С, spraying was carried out in two stages t1 = 15 min, P1 = 180 W, t2 = 15 min, P2 = 200 W (t - spraying time, P - magnetron power). Its resistivity was ρ = 20 Ω∙cm. The optical width of the band gap is Eg = 3.5 eV and absorption of light photons takes place by means of direct optical transitions. 
Studies of I-V–characteristics of anisotype p-CuCoO2/n-Si heterostructures at forward and reverse biases in the temperature range T = 299 – 343 K indicate the rectifying properties of the structures. The rectification ratio at |V| = 0.7 V and T = 294 K was ~ 103. The diode characteristics of the heterostructure are due to the energy barrier qφk ~ 0.5 eV from the n-Si side. At forward biases of 0.05 V < V < 0.4 V in the structure of p-CuCoO2/n-Si the generation-recombination mechanism of current transfer prevails. At V > 0.4 V the tunnel mechanisms of current transfer with participation of surface states prevail. The reverse current at biases – 2 V < V < – 3kT/q V is determined by tunneling processes involving surface states. The p-CuCoO2/n-Si heterostructure is photosensitive at reverse displacement under AM1.5 radiation conditions. 

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