Optoelectronic Characteristics Of GaN Based Light-emitting Diodes(LEDs) And The Negative Capacitance In DSCs

With the development of the theory and technology of semiconductor device,the optoelectronic devices based on the semiconductor material and P-N junction have been more widely used.Among them the two most typical devices are light-emitting diodes(LEDs)and solar cells.Although these two types devices have now been widely used,many physical problems about them are still unknown,which greatly restricts the development of the physical basis for the semiconductor device.In these questions,the typical experimental phenomena are the ‘efficiency droop' in GaN-LEDs and the negative capacitance in both devices,and so on.Here we mainly studies the above abnormal phenomena.The main work of this paper can be summarized as follows:1.Using various characterization methods of electrical properties,we accurately measured electrical properties of GaN-based multi-quantum-wells light emitting diodes(MQWs-LEDs)with five different well thicknesses,and analyzed and compared the electrical parameters measured by each method in detail.Using self-build AC-IV method the junction characteristics were obtained.After comparing the influence of the well thickness on electrical parameters,their detailed relationship on the well thickness was obtained.Negative capacitance in MQWs-LEDs was observed and it can be explained qualitatively with a strong recombination model.2.Combining output power of MQWs-LED with ABC model,we calculated the internal quantum efficiency,carrier concentration as well as various recombination coefficients.In addition,in A,B,C,which one has the most contribution to ‘efficiency droop' was deduced.3.After analyzing the spectral properties of MQWs-LEDs,we believed that the “blue-shift” phenomenon mainly results from Moss-Burstein effect.4.In solar cells the similar negative capacitance phenomenon of LEDs had been confirmed experimentally.Here,we accurately deduced and calculated various electrical parameters in dye-sensitized solar cells(DSCs)with a similar transport property model in LEDs.Results display that the radiative recombination will result in negative capacitance(NC).Then we proposed an equivalent circuit to explain the negative terminal capacitance in DSCs with the help of the recombination capacitance.In summary,the research results of MQWs-LEDs can not only confirm the defectiveness of Shockley's theory about the diffusion capacitance,but also contribute to optimize LEDs' performance.The deduced results of transport property in DSCs will provide a theory guidance to optimize DSCs' construction and to research the internal transport mechanism.