Scanning Probing of the Tribovoltaic Effect at the Sliding Interface of Two Semiconductors

Abstract

can be generated by the contact or sliding of a P-type semiconductor against an N-type semiconductor [7][8][9] (or semiconductor against metal [10][11][12] ), and a novel electric generator was proposed. [7] This new type of electric generator is gaining attention for that a direct current can be generated without a rectifier module. [8][9][10][11] However, the mechanism of the current generation in the CE involving semiconductors is still under debate.For the contact between a P-type semiconductor and an N-type semiconductor, the PN junction will be formed at the interface. [13,14] It is highly suspected that the built-in electric field in the PN junction makes the CE between the semiconductors different from that between conventional materials. Considering that, Wang et al. pointed out that the generation of the continuous direct current induced by the sliding of P-type semiconductor against N-type semiconductor is similar to the photovoltaic effect, and can be referred to as the "tribovoltaic effect." [15] The only difference is that the electron-hole pairs in tribovoltaic effect are excited during friction, in which the energy is released due to either the transition of electrons from the surface states of one side to that of another side in the contact or sliding, [16][17][18][19][20][21] or the energy released while forming a new bond at the interface, [22] just as it occurs in the CE between two conventional materials. [23][24][25][26] Then, the electron-hole pairs are separated by the built-in electric field and the external current flowing from the P-side to the N-side will be induced, as it occurs in the photovoltaic effect. [27][28][29] According to the tribovoltaic effect, the excitation efficiency of electron-hole pairs highly depends on the density of surface states of the semiconductors and the bonding interactions. Hence, the tribovoltaic current may be related to the density of surface states of the semiconductors and the sliding load, which can significantly affect the bonding interactions at the sliding interface. [22] In this work, the direct current is generated by sliding an N-type semiconductor tip over a Si sample surface using conductive atomic force microscopy (CAFM). [30,31] Both P-type and N-type Si samples with various doping concentrations are used in the experiments. Further, the Si samples are treated by inductively coupled plasma reactive ion etching (ICP-RIE), which can significantly increase the density of surface states of the semiconductors by doping or introducing defects on the surface. [32,33] It is revealed that the current density in the sliding experiments increases with increasing of the density of surface Contact electrification (CE or triboelectrification) is a common phenomenon, which can occur for almost all types of materials. In previous studies, the CE between insulators and metals has been widely discussed, while CE involving semiconductors is only recently. Here, a tribo-current is generated by sliding an N-type diamond coated tip on a P-type or N-type Si wafer...

Direct Current Triboelectric Nanogenerators

“…Zheng et al demonstrated a DC output based on tribovoltaic effect by using a diamond (n-type) coated AFM tip to rub on the Si wafers (Figure 7d). [113] The current will flow the p-type sample to the n-type tip through external circuit, which is consistent with the proposed tribovoltaic effect. The current mapping for p-type and n-type Si wafers with different doping concentrations and corresponding cross-sectional line analysis are shown in Figure 7e.…”

“…Obviously, the tribo-tunneling output signal polarity is determined by the surface potential difference between frictional materials. Moreover, the tribovoltaic effect in nanoscale range (Figure 7g) and the influence of the surface characteristics of the semiconductors is further studied by Zheng et al [113] A higher surface states density of the semiconductor materials can be obtained via the inductively coupled plasma reactive ion etching (ICP-RIE) treatment. Figure 8g,h compares the volt-ampere characteristic of the p-n junction before and after treatment.…”

“…Reproduced with permission. [113] Copyright 2020, Wiley-VCH. stronger release of energy for producing the electron-hole pairs, and improving the current output.…”

“…stronger release of energy for producing the electron-hole pairs, and improving the current output. [113]…”

“…The energy for exciting electron–hole pairs comes from two aspects; one is the energy released by the transfer of electrons from the higher energy surface states of the diamond tip to the lower energy surface states of the silicon after contact; and the other is energy released due to the formation of bonds on the p–n junction during sliding (Figure 8j,k). [ 113 ] Under the action of interfacial electric field, the excited electron–hole pairs are separated to generate DC output, as shown in Figure 8l. It can be found that the higher the density of surface states, the more electrons transfer between the surface states, resulting in stronger release of energy for producing the electron–hole pairs, and improving the current output.…”