Friction-Dominated Carrier Excitation and Transport Mechanism for GaN-Based Direct-Current Triboelectric Nanogenerators

Abstract

The semiconductor triboelectric nanogenerator (TENG) based on the tribovoltaic effect has the characteristics of direct current and high current density, but the energy transfer and conversion mechanism is not completely clear. Here, a series of gallium nitride (GaN)-based semiconductor direct-current TENGs (SDC-TENGs) are investigated for clarifying the carrier excitation and transport mechanism. During the friction process, the external output current always flows from GaN to silicon or aluminum, regardless of the direction of the built-in electric field, because of the semiconductor types. These results reveal that the carrier transport direction is dominated by the interfacial electric field formed by triboelectrification, which is also verified under different bias voltages. Moreover, the characteristics dependent on the frictional force have been systematically investigated under different normal forces and frictional modes. The open-circuit voltage and short-circuit current of SDC-TENG are both increased with a larger frictional force, which shows that the more severe friction results in both a larger interface electric field and more excited carriers. The maximum voltage can reach 25 V for lighting up a series of LEDs, which is enhanced by four times compared to the cutting-edge reported SDC-TENGs. This work has clarified the friction-dominated carrier excitation and transport mechanism for the tribovoltaic effect, which demonstrates the great potential of semiconductor materials for frictional energy recovery and utilization.

Direct-Current Triboelectric Nanogenerators Based on Semiconductor Structure

“…The authors explained that tribovoltaic effect is not dominated by the built-in electric field formed by the p–n junction but the interface electric field formed by the continuous friction dominates, because the direction of the internal junction current is always from Bi 2 Te 3 to GaN and the tribovoltage is equal to the applied bias voltage (when I sc = 0) regardless of the semiconductor type. Similarly, Chen et al verified the carrier excitation and transport mechanism of a designed GaN–Si heterojunction for a GaN-based DC TENG (Figure i). To prove the point that the carrier transport direction is dominated by the interfacial electric field formed by triboelectrification they applied different bias voltages on n + GaN–Si (0 V, 2 V, −4 V, and −8 V) and pGaN–Si (0 V, 1 V, −1 V, and −2 V).…”

“…(j) Open circuit voltage and (k) short-circuit current of nGaN–Si and pGaN–Si DC TENG. Reproduced with permission from ref . Copyright 2022 American Chemical Society.…”

“…(b) Magnified image from red dotted box of panel a. Data from refs − , , − , , , , , , , , , , and .…”

“…Nevertheless, friction materials treated by these methods tended to be less stable. In recent years, researchers found that semiconductors can also produce charge transfer by rubbing against another material and could generate direct current (DC) with high density, which gives them an advantage over conventional TENGs. − Therefore, the triboelectrification phenomenon between semiconductors has been given more and more attention. − It is noteworthy that the third-generation semiconductor materials (for instance, gallium nitride (GaN)) have the characteristics of large bandgap width, high breakdown field strength, and high electron saturation speed, which can achieve excellent output performance for nearly two years as a new friction materials. − …”

Coexistence of Contact Electrification and Dynamic p–n Junction Modulation Effects in Triboelectrification

“…It is well known that at least one insulator is needed as the triboelectric material to make a TENG; otherwise, there would be no induction charges across the insulating layer. Other types of materials have also been explored for the fabrication of TENGs, including traditional semiconductors, organic semiconductors, piezoelectric materials, 2D materials, and so forth. , Dynamic contact between a metal and a semiconductor and that between two semiconductors also demonstrated electrical outputs with energy conversion capability, which have been attributed to the modulation of the Schottky barrier or p–n junction. ,− …”