Study On The Photo-generated Carrier Transport Properties In Multiple Quantum Wells Structures

According to the traditional classical theory,there is a strong quantum confinement effect in semiconductor multi-quantum wells(MQWs)structure,which can effectively capture and confine the carriers.Therefore,MQWs structure is widely used in the preparation of electro-optical converters,such as light-emitting diodes,lasers,etc.However,MQWs structure has a strong confinement on the photo-generated carriers generated by direct transition under light excitation.The application of MQWs structure in the field of photo-electric conversion is limited due to its strong quantum confinement effect.However,recent experimental studies have found that there is a strong escape phenomenon of photo-generated carriers in PIN structure(MQWs structure is placed in PN junction,hereinafter referred to as PIN structure).In the case of resonant excitation or non-resonant excitation,there are open circuit voltage and short circuit current.The photoluminescence(PL)peak in the case of short circuit has more than 80% attenuation,which indicates that photo-generated carriers can effectively escape from the MQWs structure.As a contrast,no obvious decrease of PL peak is found in the case of short circuit in NIN structure(MQWs structure is placed in two N region,hereinafter referred to as NIN structure),even in the case of applied electric field.In order to further research the transport and transfer of photo-generated carriers in PIN structure,ultrafast time-resolved spectroscopy based on pump-probe technique is used to directly observe the carrier escape phenomenon.By comparing the dynamic behavior of photo-generated carriers in PIN structure and NIN structure under open circuit and short circuit,it is concluded that the photogenerated carriers in PIN structure escape into the external circuit preferentially rather than recombination.However,the dynamic behavior of photo-generated carriers in NIN structure is basically the same under open circuit and short circuit conditions.Next,by changing the thickness of the ? region(MQWs region)in the PIN structure,the escape distance(or time)of the photogenerated carriers is different.It is found that the larger the thickness of the ? region is,the longer the lifetime of the photogenerated carriers is,but it is less than that of the photo-generated carriers in the NIN structure,indicating that the photo-generated carriers in PIN structure are preferentially escaping rather than recombination.In order to deeply understand the differences between PIN structure and NIN structure,as well as the differences in the transport of photo-generated carriers,this paper analyzes the energy band structure,internal electric field intensity distribution and distribution of photogenerated carriers of PIN structure and NIN structure,and obtains the following conclusions: the energy band in PIN structure is inclined in a single direction,and the built-in field is uniformly distributed,and the energy band in NIN structure is inclined in double directions even after the applied electric field.The energy band diagram and built-in field of NIN structure are very different from that of PIN structure,and there is a large potential barrier for the hole in the NIN structure,so that the hole can not escape from the NIN structure,so the photoluminescence peak will not decay obviously.Aiming at this phenomenon,we continue to simulate PIP type MQW structure(MQW structure is placed in two P regions,hereinafter referred to as PIP structure).It is found that there is a large potential barrier relative to the electron in PIP structure,so that the electron can not escape from PIP structure,so the PL peak will not have obvious attenuation phenomenon.The related PL testing experiments also confirms this conclusion.In the process of simulation analysis,it is found that although there are essential differences between the NIN structure and the PIN structure,there is a high similarity between some regions of the NIN structure and the PIN structure after the external electric field is applied,which indicates that the carriers in some regions of the NIN structure may escape after the external electric field is applied.To explore it,we continue to study the case of two types of quantum wells in NIN structure.The experimental results show that the PL peaks of the NIN structure would transfer to the other from one when the external electric field is applied in different directions,which indicates that the photo-generated carriers in the NIN structure transfer in the ? region.The research work in this paper is helpful to better understand the transport behavior of photo-generated carriers in MQWs structures,and to design new photoelectric converters.