InP/Si Heterostructure for High-Current Hybrid Triboelectric/Photovoltaic Generation

Harvesting hybrid mechanical and solar ambient energy with one small device remains a challenge. Here, we report on producing electric current using a Schottky type metal-oxide-semiconductor structure formed by an n-InP layer covered with native oxide and an atomic force microscope (AFM) probe with a conductive coating. The tip’s sliding reciprocating motion during AFM scanning in contact mode produces a direct current signal in the probe-sample circuit. Two electric power generation mechanisms exist. A strong current was detected under sample illumination because of a photovoltaic effect with efficiency of 7% at the Si/InP heterojunction. Having the sample set in complete darkness, we observed current pulses of the opposite polarity, which suggests the existence of another mechanism not connected to photogeneration. This dark current originates from the tunneling of triboelectrically induced charge redistribution on the metal/oxide interface. The current polarity corresponds to electronic quantum mechanical tunneling through the oxide layer from the metal tip into InP. The current density exceeded 15 kA/m2. This is 2 and more than 4 orders greater than that in silicon- and polymer-based triboelectric nanogenerators, respectively. The open-circuit voltage value was 15 mV, and output electric power reached 110 W/m2. Understanding of triboelectric phenomena in photovoltaic semiconductor materials will allow creation of a new type of high-current hybrid energy devices that combine triboelectric nanogenerators and solar cells.