Research Of The Carrier Transport And Material Growth Of ?-N Photodiode Detectors

The photodetectors based on ?-nitride materials are potentially applied in light communication,smoke alarm,biological and chemical detections.Although significant progress has been achieved in the past few decades,the ?-nitride based photodetectors have also faced with many problems.For example,the AlGaN based ultra-violet photodetectors are still inefficient for commercialization.One of the most important issues is the difficulty to obtain high-quality and high Al content materials,which limits the device performance for further improving.In this thesis,we focus on the methods to improve the performance of ?-nitride based photodetectors: on one hand,from the basic physical process of photo-electric conversion,we have studied the light absorption and carries transport process in the P-i-N quantum well structure under resonant excitation,which gives us a new insight into the quantum well photodiode detectors.On the other hand,to obtain good crystal quanlity,we have proposed a spatial separated source delivery(SSSD)method to achieve the epitaxy of high quanlity and high Al content materials.The main contents of our work are summarized as follows:1)The carriers transport properties of quantum wells in P-N junction.We used quantum wells as the i-layer for a P-i-N structure and N-i-N structure.By comparing with the N-i-N structure,we have studied the carriers transport properties in the quantum wells of P-i-N structure under resonant excitation mode.The results indicate that most of the resonantly excited photo-generated carriers are extracted from the quantum wells rather than relax to ground state for recombination,whether the P-N junction is under short circuit or reverse bias condition.However,applied an external bias to the N-i-N structure,most of the resonantly excited photo-generated carriers relax to ground state for recombination.Thus appling an external bias to N-i-N structure can't implement the same effect of P-N junction.At the same time,the calculated photon absorption is also enhanced.This shows the P-N junction have played a special role in carriers' escaping from the quantum wells,thus the carrier absorption and transportation processes are enhanced.This provides us a new knowledge of the quantum well photodiode detector for a better performance.2)A spatial separated source delivery(SSSD)method has been proposed by a well-designed flow flange and source delivery pipeline.This method can alleviate parasitic reactions between group ? precursors and ammonia(NH3)in gas phase by avoiding the unwanted mix of different groups of sources in gas phase.And it is demonstrated that the reactions are controlled to change from combination reactions in traditional MOCVD system to pyrolysis reactions and surface reactions in the SSSD mothod.The influence of our SSSD method on the epitaxy of AlGaN materials has been investigated systematically.For Ga N,the growth rate has also been promoted and a remarkable reduction of the sources consumption is achieved.During the epitaxy of AlGaN materials,the aluminum composition and crystal quanlity have been greatly enhanced.At last,good-uniformity,high-quality and high Al content materials have been achieved.As a result,the SSSD method provides better AlGaN materials for the improving performance of AlGaN ultra-violet photodetectors.