Photovoltaic properties and barrier heights of single-crystal and polycrystalline Cu2O–Cu contacts

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Abstract
The spectral distribution of the photovoltaic response of polycrystalline and single‐crystal Cu2O–Cu contacts was measured at room temperature using a chopped light technique. The single‐crystal contacts were formed by reducing the (111) surface of single‐crystal Cu2O to copper using atomic hydrogen at room temperature. Prior to the reduction, a departure from stoichiometry was induced in the single crystals by treatment at 750 or 960°C in a known and controllable partial pressure of oxygen. The polycrystalline contacts were prepared from polycrystallinecopper plate partially oxidized to Cu2O at 1000°C. The photoresponse measurements indicate that the dominant photovoltaic mechanisms in Cu2O–Cu contacts are hole photoemission from Cu into Cu2O when hv < Eg and electron injection from Cu2O into Cu when hv > Eg . Barrier heights determined from the threshold of the hole photoemission process measured 0.75±0.06 eV for the single‐crystal contacts and 0.75±0.02 eV for the polycrystalline contacts. It is shown that the observed variation in the barrier height of the single‐crystal contacts may be due to barrier lowering by the Schottky effect.

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