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Using simple graphene transfer and the laser lift-off process for a non-centrosymmetric GaN layer on a flexible polydimethylsiloxane (PDMS) substrate, the piezotronic effect by strain-induced current-voltage measurements at the two end points is studied. By inducing compressive strain on the flexible graphene/GaN/PDMS sensor, the Schottky barrier between the graphene and GaN/PDMS heterojunction can be electro-mechanically modulated by the piezotronic effect. It is observed that the flexible graphene/GaN/PDMS sensor is sensitive to various applied compressive and tensile strains in the positive/negative bias scans. The sensor is extremely sensitive to a compressive strain of -0.1% with a gauge factor of 13.48, which is 3.7 times higher than that of a standard metal strain gauge. Furthermore, the sharp response of the flexible graphene/GaN/PDMS sensor under the -0.1% compressive strain is also investigated. The results of this study herald the development of commercially viable large-scale flexible/wearable strain sensors based on the strain-controlled piezotronic effect in future investigations.

Temperature-based organic–inorganic photodiodes have recently become attractive applications in branches of science and technology with eco-friendly and hybrid concepts. Here, we describe the use of salmon DNA (SDNA) biomolecules as temperature and light sensors. We demonstrate the temperature- and light-sensitive mechanism of polarity switching in metal/organic/n-GaN bio-hybrid photodiodes based on salmon DNA-cetyltrimethylammonium chloride (SDNA-surfactant). The SDNA-surfactant/n-GaN bio-hybrid temperature photodiode (Bio-HTPD) shows negative bias shift of current (I)–voltage (V) plots by 0.70 and 0.42 V compared to zero-bias at temperatures of 275 and 300 K, respectively, under light illumination. However, the I–V plots of the Bio-HTPD moved towards positive bias by 0.08 V compared to zero-bias at 325 K under light irradiation. This phenomenon resulted in electrically negative photocurrents up to room temperature, which remarkably switched to positive photocurrents at above room temperature. The temperature variations are closely associated with charge activation and unidirectional transport in the SDNA-surfactant biomolecule. Moreover, the change from negative to positive photocurrent could be related to high electron–hole pair generation at higher transition temperature. The formation of an energy band model with thermal hopping is proposed, which explains the reasonable charge transport mechanism.

Flexible devices have attracted considerable attention because of their very productive applications in the diverse areas such as healthcare, artificial intelligence, and robotics. Accordingly, in this study, we fabricated a flexible nano-sized GaN thin-film device via a double-transfer method using a laser lift-off process from sapphire with thermal tape and then with carbon tape onto a polycarbonate substrate. With the application of compressive/tensile strains, the flexible nano-sized GaN thin-film device can be mechanically controlled by the piezotronic effect. The device has excellent electromechanical performance with a gauge factor of 2206 at a compressive strain of 0.32%, which is nearly 11.11 times greater than that of a conventional strain-gauge value. Furthermore, the device shows an effective ON condition in the compressive direction and OFF condition in the tensile direction at an applied bias voltage of 0.5 V. The fabricated device has potential for innovative and advanced applications such as human–machine interfaces, biomedical diagnoses, prostheses, intelligently controlled rooms, and active flexible electronics.

Recently, considerable interest have occurred in the development of an organic-inorganic-based bio-hybrid photodiodes (Bio-HPDs) with metal-free, eco-friendly, and cost-competitive features for light-sensitive devices. This paper reports a bio-inspired optical absorber material for the fabrication of Bio-HPDs using n-type hydrogenated amorphous silicon (a-Si:H) and a natural deoxyribonucleic acid (DNA)-cetyltrimethylammonium chloride (CTMA) biomaterial. a-Si:H is inexpensive and abundant, and DNA-CTMA is metal-free and eco-friendly. A DNA-CTMA coating on n-type a-Si:H leads to a chemically stable material with increased absorption and effective ties of dangling bonds and interface state density. Analysis results showed that the rectification ratio (RR) of the Bio-HPD is found to be 4 times higher than reference PD. This indicates that the effective RR is improved by the DNA-CTMA layer since it creates molecular charge interactions between DNA-CTMA layer and a-Si:H substrate. Moreover, Bio-HPD shows a light photosensitivity (Iphoto/Idark) of 474 with more reliable and has longer life time. In addition, the formation and feasible charge transport mechanisms are discussed. This biomaterial can be used for the development of commercially viable and environmentally safe large-scale Bio-HPDs applications.

A deoxyribonucleic acid-cetyltrimethylammonium chloride (DNA-CTMA) biopolymer-based inorganic p-type GaN bio-hybrid Schottky photodiode was fabricated and its electrical characteristics were studied. The Al/Cr/DNA-CTMA/p-GaN bio-hybrid photodiode parameters were investigated using current-voltage (I-V), capacitance-voltage-frequency (C-V-f) and conductance-voltage-frequency (G/ω-V-f) measurements. The calculated ideality factor and barrier height of the diode were found to be 1.8 and 0.82 eV, respectively. The electrical and photo-conduction properties of the diode were examined using dark I-V and steady-state photoconductivity techniques. The C-V-f and G/ω-V-f measurements showed that the capacitance and conductance of the diode depends on the bias voltage and frequency, respectively. On the other hand, a decrease in capacitance and increase in conductance with increasing frequency at room temperature were demonstrated based on the interface state density. In addition, the interface state density decreased exponentially with increasing frequency. It is also noted that series resistance decreased with increasing frequency. The results showed that the biopolymer-based Al/Cr/DNA-CTMA/p-GaN bio-hybrid photodiode can be used as a photosensor in optical applications and the development of high-performance organic-inorganic-based p-Schottky diodes that are environmentally safe.

We used simple graphene transfer and microwave synthesis to deposite wurtzite-structured CdS nanospheres with gold nanoparticles (AuNPs) on a flexible polyethylene terephthalate (PET) substrate. The temperature dependence of the piezotronic effect of the CdS nanospheres was studied in the temperature range 240–320 K under tensile strains of 0.00–0.40%, the effect was found to significantly depend on the device temperature. Moreover, the piezotronic effect was enhanced by over 590% at a strain of 0.40% by cooling temperature owing to the improved efficiency of piezoelectric potential charges. This is a result of the decreased screening effect by reduced carrier generation in the CdS. In addition, the consistent charge transfer mechanism in the investigated piezotronic device is explained by the possible energy band diagrams. The results of this analysis provide a comprehensive understanding of the piezotronic effect and provide a direction for future device applications in fields such as health monitoring, human-machine communication, surgical robotics, and artificial intelligence.

In this work, a deoxyribonucleic acid-cetyltrimethylammonium chloride (DNA-CTMA) biomaterial based p-type hydrogenated amorphous silicon (a-Si:H) photodiode (PD) is fabricated and its electrical characteristics are investigated. The Al/DNA-CTMA/p-type a-Si:H PD parameters are studied using current-voltage (I-V), capacitancevoltage-frequency (C-V-f) and conductance-voltage-frequency (G/ω-V-f) measurements. The barrier height and the ideality factor of the diode are found to be 0.78 eV and 1.9, respectively. The electrical and photoconductivity properties of the diode are analyzed by using dark I-V and transient photocurrent techniques. The C-V-f and G/ω-V-f measurements indicate that the capacitance and conductance of the diode depend on the voltage and frequency, respectively. The experimental results reveal that the decreases in capacitance and the increases in conductance with an increase in frequency can be explained on the basis of interface states (NSS). Series resistance (RS) measurements are performed on the diode and discussed here. The obtained electrical parameters confirm that the Al/DNA-CTMA/p-type a-Si:H PD can be used as an optical sensor for the development of commercial applications that are environmentally benign.

The temperature-dependent electrical properties and carrier transport mechanisms of tetramethylammonium hydroxide (TMAH)-treated Ni/Au/Al2O3/GaN metal–insulator–semiconductor (MIS) diodes have been investigated by current–voltage (I–V) and capacitance–voltage (C–V) measurements. The experimental results reveal that the barrier height (I–V) increases whereas the ideality factor decreases with increasing temperature. The TMAH-treated Ni/Au/Al2O3/GaN MIS diode showed nonideal behaviors which indicate the presence of a nonuniform distribution of interface states (N SS) and effect of series resistance (R S). The obtained R S and N SS were found to decrease with increasing temperature. Furthermore, it was found that different transport mechanisms dominated in the TMAH-treated Ni/Au/Al2O3/GaN MIS diode. At 150 K to 250 K, Poole–Frenkel emission (PFE) was found to be responsible for the reverse leakage, while Schottky emission (SE) was the dominant mechanism at high electric fields in the temperature range from 300 K to 400 K. Feasible energy band diagrams and possible carrier transport mechanisms for the TMAH-treated Ni/Au/Al2O3/GaN MIS diode are discussed based on PFE and SE.