Guoying Yan

Large lateral photovoltaic effect in a-Si:H/c-Si p–i–n structure with the aid of bias voltage

In this paper, for the first time, we report a significant enhancement of the lateral photovoltaic effect (LPE) in a hydrogenated amorphous silicon/monocrystalline Si (a-Si:H/c-Si) p–i–n structure via the application of a transverse bias voltage. The position sensitivity of this a-Si:H/c-Si p–i–n structure increased linearly with both laser power and wavelength, and the position sensitivity reached a minimum of 809 mV/mm for a 980 nm laser, which was approximately 43 times larger than that without the bias voltage. Moreover, this structure exhibited good linearity with nonlinearity of no more than 3%. We attribute this greatly improved LPE to the enhanced Schottky-barrier-dependent transmitted possibility of photo-generated holes.

Magnetic field-modulated photo-thermo-electric effect in Fe/GaAs film

Ferromagnet/semiconductor heterostructure, such as Fe/GaAs, is always one of the key issues in spintronics due to its prerequisite for the realization of spin sensitive devices. In this letter, a lateral photoelectric effect (LPE) was observed in Fe/GaAs. Our results show that the sensitivity was not related to laser wavelength, but only proportional to laser power, suggesting that the lateral photovoltage was induced by photo-thermo-electric effect. Moreover, we also observe that the voltage signal increases with the increase in applied field due to decreasing scattering probability for spin-polarized electrons. Our finding of LPE adds another functionality to the Fe/GaAs system and will be useful in development of spin-polarized voltage devices.

The enhancement of photo-thermo-electric conversion in tilted Bi 2 Sr 2 Co 2 Oy thin films through coating a layer of single-wall carbon nanotubes light absorber

Light-induced transverse thermoelectric effect has been investigated in c-axis tilted Bi(2)Sr(2)Co(2)O(y) thin films coated with a single-wall carbon nanotubes light absorption layer. Open-circuit voltage signals were detected when the sample surface was irradiated by different lasers with wavelengths ranging from ultraviolet to near-infrared and the voltage sensitivity was enhanced as a result of the increased light absorption at the carbon nanotubes layer. Moreover, the enhancement degree was found to be dependent on the laser wavelength as well as the absorption coating size. This work opens up new strategy toward the practical applications of layered cobaltites in photo-thermo-electric conversion devices.

Dependence of oxygen content on transverse thermoelectric effect in tilted Bi 2 Sr 2 Co 2 O y thin films

The transverse thermoelectric (TE) effect has been investigated in c axis tilted Bi2Sr2Co2Oy thin films with different oxygen content. The film samples were fabricated by a chemical solution deposition method annealed under different atmospheres of O2, air, and N2, respectively. Open-circuit transverse voltage signals were observed when the surface of the films was heated by a pulsed laser as well as a continuous thermal source. With the increase of oxygen content in the films, the amplitude of the observed voltage signals increased while the response time decreased. The experimental results can be explained by a mechanism involving the transverse TE effect as well as the transport theory of TE materials.

Enhanced light-induced transverse thermoelectric effect in c-axis inclined BiCuSeO thin films via Pb doping

The great enhancement of light-induced transverse thermoelectric effect in c-axis inclined BiCuSeO thin films has been achieved by Pb doping. Large open-circuit thermoelectric voltage signals are all observed in the inclined Bi1-xPbxCuSeO (x = 0, 0.04, 0.08) films when the film surface is irradiated by a 308nm pulsed laser. As the Pb doping content increases, the magnitude Vp of the induced voltage signal increases greatly while the response time τ decrease obviously. A large figure of merit Vp/τ of about 236.7 mV/ns is obtained in the 8% Pb-doped film sample under the 308 nm pulsed irradiation with energy density of 0.5mJ/mm2, which is about 25 times larger than that in the undoped film. Possible mechanism is proposed to explain the experiment results. This work might pave the way for the practical application of BiCuSeO-based thin films for high sensitive and fast response ultraviolet pulsed photodectors.

Light-induced transverse voltage effect in c-axis inclined BiCuSeO single crystalline thin films

Light-induced transverse voltage effects in c-axis inclined BiCuSeO thin films have been investigated by using different lasers with the wavelength ranging from ultraviolet (UV) to near infrared (NIR). Open-circuit voltage signals are all clearly observed when the film surface is irradiated by these lasers. Especially, a very large voltage signal with a magnitude exceeding several volts is obtained under the irradiation of the UV pulsed laser, and the voltage polarity of this signal is reversed when the sample is irradiated from the substrate side. A possible mechanism based on the transverse thermoelectric effect is proposed to explain the above experiment results. This work demonstrates the potential application of BiCuSeO for broad-band photodetectors, especially for UV pulsed light detection.

Enhanced transparent conducting performance of c-axis oriented Ca3Co4O9 thin films

p-type transparent conductive Ca3Co4O9 thin films were grown on LaAlO3 substrates using a pulsed laser deposition technique. The films showed perfect c-axis orientation with a resistivity of about 7.3 mΩ cm at room temperature and optical transmittance of about 50% in the visible range. A high figure of merit of about 988 MΩ−1 was achieved in these c-axis oriented Ca3Co4O9 films, which is comparable to those reported for the state-of-the-art p-type transparent conducting oxides. This work demonstrated the potential applications of c-axis oriented Ca3Co4O9 films in optoelectronic devices as a new class of transparent conducting oxide coatings.

Large Near-Infrared Lateral Photovoltaic Effect of ITO/Si Structure Observed at Low Temperature

In this paper, the power- and wavelength-dependent lateral photovoltaic effect (LPE) in an indium tin oxide/Si structure is first studied at different temperatures ranging from 292 to 80 K. It was found that the position sensitivity increased gradually until it became saturated with increasing laser power at a constant temperature, and the saturated position sensitivity increased nearly linearly from 2.47 to 3.91 mV/mm with increasing wavelength from 405 to 980 nm at 292 K. More importantly, the position sensitivity also increased considerably with decreasing temperature from 292 to 80 K, and the position sensitivity of 7.47 mV/mm at 80 K is about 1.91 times as large as that of 292 K under illumination of 70 mW for 980-nm laser. Based on the temperature-dependent Schottky barrier height, these results can be well explained. The significant observation of the improved LPE in infrared region makes this structure great potential in infrared position sensitive detectors, especially at low temperature.

Light-induced transverse thermoelectric effect in miscut GaAs single crystals by far-infrared laser illumination

Light-induced transverse voltage (LITV) effect was investigated in miscut GaAs (0?0?1) single crystals by a 10.6??m continuous wave CO2 laser with low power density. Open-circuit voltage signals were observed when the sample surface was illuminated by the 10.6??m radiation and the magnitude of the voltage increased linearly with the miscut angle as well as the laser power on the samples. The voltage sensitivity can be improved after coating a layer of graphite light absorber on the surface of the sample. Moreover, open-circuit voltage signals were also detected when the surface of the samples was heated by a thermal heater. The results suggest that the LITV in miscut GaAs single crystals mainly originates from the transverse thermoelectric effect. This work demonstrates that the miscut GaAs single crystals have potential applications for detecting optical and thermal radiations.

Photoresponse in tilted Bi2Sr2Co2Oy thin films with nano-structured silver layer as the light absorber

Layered cobalt oxide thin films with tilted structures exhibit large light-induced transverse voltage signals due to the transverse thermoelectric effect and have great potential applications in uncooled broad-band light detectors. In this paper, we investigated the photoresponse in c-axis tilted Bi2Sr2Co2Oy thin films coated with a layer of nano-structured silver light absorber by using a 532 nm continuous wave laser as the incident light. The incidence direction of the laser beam was directly perpendicular to the sample surface. The laser spot was located at the centre position between the two electrodes and its diameter was about 2 mm. The induced lateral voltage signals were recorded using a 2400 Keithley source meter. Open-circuit voltage signals were observed when the sample surface was illuminated by the 532 nmradiation. Appropriate lateral size and thickness of the nano-structured silver layer can increase the photo-thermal-electric conversion efficiency in this photoresponse process due to the effective absorption of the light at the absorption layer, leading to the improvement in voltage sensitivity. The result offers important guidance of designing the light absorption layer for high performance broad-band light detectors based on the light-induced transverse voltage effect.