Photoluminescence study of ZnO∕Mg0.1Zn0.9O quantum wells with graded well width (Lw) was carried out at 4.2K. The emission evolution from quantum confinement regime to quantum-confined Stark regime was observed clearly. For large Lw, the emission splits into two peaks which are attributed to the emissions of ZnO band edge and separately localized carriers, respectively. The internal electric field in the well layer was estimated to be ∼0.3MV∕cm, being similar to previous reports. The results are useful in designing ZnO QW based optoelectronic devices.
In diffusion to blue light-emitting diode (LED) wafers is performed by the inductive coupled plasma (ICP) treatment of a covering layer of indium tin oxide (ITO) on the wafer surface. The electrical property of the ptype contact is improved and the redshift of photoluminescence (PL) from the InGaN quantum well of the wafer is found. Measurements by x-ray photoelectron spectroscopy (XPS) demonstrate that In atoms have diffused into p-GaN. Reflectance spectra of the sample surface reveal the variation caused by the ICP treatment. A model of compensation of the in-plane strain of the InGaN layer is used to explain the redshift of the PL data. Finally, LEDs are fabricated by using as-grown and ICP-treated wafers and their properties are compared. Under an injection current of 20 mA, LEDs with ICP-induced In doping show a decrease of 0.3 V in the forward voltage and an increase of 23% in the light output, respectively.
We demonstrated vertical-structured InGaN/GaN multiple-quantum-well (MQW) solar cells with enhanced performances at a wavelength of 510 nm. The enhancement was achieved by using a ptype ohmic mirror with a combined indium-tin-oxide film and an aluminum (Al) reflector inserted beneath the MQW absorption region. In addition, both good ohmic contact and high reflection were observed. The vertical-structured MQW solar cell with an Al reflector exhibited significant improvements in device performances as compared to that without the Al reflector, including a 49% increase in the short-circuit current density and a 56% increase in the power conversion efficiency.
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