Recently, to sandwich InAs QDs with GaAs1-xSbx layers have attracted enormous attention. It is expected to achieve a transition from type-I to type-II band alignment at ~ x=12%. The type-II InAs/GaAs1-xSbx QDs are predicted to be one of the optimizing active region materials for achieving high efficient intermediate-band solar cells.
We first investigate PL properties of InAs/GaAs1-xSbx QD structures of different Sb compositions (x=0, 0.15, and 0.25) in the GaAs1-xSbx capping layer. By capping the InAs QDs with GaAs0.85Sb0.15 and GaAs0.75Sb0.25 layer, we are able to gain type II QDs. These type II QDs exhibit a clear multi-peaks characteristic under increasing laser excitation intensity, which stems from different carriers recombination routes due to the combination of InAs QDs with GaAs1-xSbx capping layer. Time-resolved PL measurements further confirm our assignment for the mnulti-peaks in the PL spectra. We then study carrier coupling inside vertically aligned InAs/GaAs and InAs/GaAs1-xSbx QD pairs. The features of InAs/GaAs1-xSbx QD pairs are very different from the traditional InAs/GaAs QD-pairs. Again, clear multi-peaks characteristic are observed under stronng laser excitation intensity, which stems from different carriers recombination routes from the top InAs/GaAs1-xSbx QDs.
Our investigations indicate that the optical behavior and carrier dynamics in type-II InAs/GaAs1-xSbx QDs and QD-pairs are much more complicated than the InAs/GaAs QDs counterparts. This study provide useful information for understanding the band structure and carrier dynamics of the InAs/GaAs1-xSbx QDs for high efficiency solar cell applications.
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 Bi<sub>2</sub>Sr<sub>2</sub>Co<sub>2</sub>O<sub>y</sub> 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.
this paper, we have prepared c-axis inclined Na<sub>x</sub>CoO<sub>2</sub> thin films on 10° and 20° tilted c-Al<sub>2</sub>O<sub>3</sub> substrates and studied its light-induced thermoelectric voltage effect by using an ultraviolet pulsed laser as light source. A giant open-circuit voltage signal with the peak voltage V<sub>p</sub> of tens of voltage was observed when the film surface was illuminated by the 308 nm pulsed radiation, and the V<sub>p</sub> increased linearly with the inclination angle as well as the laser energy on the film. In addition, we found that Ag doping in Na<sub>x</sub>CoO<sub>2</sub> films can improve the sensitivity of the thermoelectric voltage signal. The results demonstrate that c-axis inclined Na<sub>x</sub>CoO<sub>2</sub> thin film has a great potential application in the detection of weak ultraviolet pulsed radiation.