Study On The Performance Of The Photoelectric Devices Based On Nitride Multi-quantum Wells Structure

Based on the materials of Gallium Nitride(Ga N),technology of the light-emitting diodes(LEDs)in blue and green light-emitting wavelength is mature,and the industrial production has already been achieved.In the field of solid lighting,it is very important to realize GaN based white light LED.At present,the technology to realize white light LED is mainly achieved through the method that blue light LED or ultraviolet LED to activate phosphor powder.But the method which needs to add phosphor increases the complexity of the technological process of LED.According to the theoretical analysis of quantum mechanics and semiconductor physics,multiple quantum wells(MQWs)structure as the active layer of the LED can restrain the carriers and improve the illuminous efficiency.In the conventional blue light LED structure,which contains the MQWs structure in PN junction,the photo-excited carriers should be limited in the quantum well under the resonance excitation mode.However,the photo-excited carriers escape from the MQWs,and generate open circuit voltage or short circuit current in the external circuit.Meanwhile,the intensity of photoluminescence under the condition of short circuit has weakened a lot.These phenomena show that the MQWs structure in PN junction has a contradiction with the traditional theoretical analysis about the carrier transport.For the purpose of improving performance of photoelectric devices and aiming at those problems mentioned above,two points have been payed intention in our work.First,a structure of hybrid MQWs LED has been designed,then grown by metal organic chemical vapor deposition(MOCVD)method,and has realized single chip white light LED.Second,systematic measurement and analysis are carried out for the abnormal carrier transport in the MQWs structure with PN junction,and corresponding physical mechanism and carrier transport model are proposed.The main contents are listed as follows:(1)We design a structure of hybrid MQWs LED,and successfully obtain single chip white light LED.With the injection current of 20 mA,the emitting light of the structure shows white color,which means that white light LED without utilizing phosphor has been achieved.Photoluminescence(PL)of resonance excitation mode at different temperature has been conducted on the structure.The results show that the density of localized states are higher,which will help to get better material quality of yellow light well layer and improve the emitting efficiency in range of long wavelength.(2)we systematically measure and analysis the abnormal carrier transport in the MQWs structure with PN junction,and propose corresponding physical mechanism and carrier transport model.In the systematical experiment of the MQWs with PN junction,open-circuit voltage or short-circuit current can be measured under the resonance excitation mode of 405 nm.By comparing the photoluminescence spectra of these two external circuits condition,it is been observed that the intensity of PL in short circuit has reduced significantly.Therefore,the photo-excited carriers are not been confined in the well,but escape from the quantum well.But,the phenomenon that photo-excited carriers escaping from the quantum well is not found in quantum well structure with NN junction,thus the effect of thermal excitation or tunneling that cause the carrier to escaping the quantum well can be excluded.Then,the physical mechanism and carrier transport model are proposed,and it is believed that the photo-excited carriers can directly escape from the quantum well under the effect of the electric field of the PN junction,and radiative recombination occurs after the process of photo-excited carriers escaping.