Analysis And Preparation Of Mushroom-mesa Photodetectors

Since its birth,optical fiber communication has become the main transmission mode of various communication networks due to its unparalleled advantages,such as extra-large communication capacity and extra-long transmission distance.At present,the advancement of the Broadband Chinese strategy;the arrival of the 5 G era;the construction of Fiber To The X;and the development of applications such as the Internet,big data,and cloud computing provide an unprecedented opportunity for optical fiber communication.Photodetectors,one of the key components of optical communication systems,are responsible for converting optical signals into electrical signals.Photodetector performance is a key factor in measuring the efficiency of an entire system.PIN photodetector,which is the most widely used photodetector in optical communication systems,has a simple structure and achieves excellent performance.However,the tradeoff between efficiency and response speed limits the improvement of the PIN photodetector's performance.To overcome this problem,we proposed a reflection-enhanced high-speed photodetector that integrates a mushroom-mesa p-i-n structure on a two-dimensional(2D)nonperiodic focusing grating.Mushroom-mesa structures have been theoretically proven capable of improving photodetector performance.The key process of preparing the mushroom-mesa structure was carried out in the experiments.Mushroom-mesa photodetectors with a 3 dB bandwidth of 24.1 GHz were fabricated.The research results and innovations of this study are as follows.1.We proposed a reflection-enhanced high-speed photodetector that integrates a mushroom-mesa p-i-n structure on a 2D nonperiodic focusing grating.This structure not only eases the bandwidth efficiency limitation of conventional p-i-n photodetectors but also obtains a high frequency response and responsivity.2.We designed and optimized the structure of mushroom-mesa photodetectors.The diameter of the absorption layer(d)is the most critical factor of high-speed performance and quantum efficiency.We studied the effect of the ratio of the absorption layer diameter(d)to the device diameter(D)on device performance.We designed a mushroom-mesa photodetector with a device diameter of 30 ?m and an absorption layer thickness of 0.5?m.When the ratio of the diameter of the absorption layer(d)to the diameter of the p-InP or n-InP layer(D)is approximately 0.5,the 3 dB bandwidth of the designed mushroom-mesa photodetector is 38.5 GHz.The external quantum efficiencies are 33.4%and 24.9%with and without grating,respectively.3.The mushroom-mesa structure was prepared using wet etching.The undercut etching rate is approximately 0.3 ?m/min.4.Mushroom-mesa photodetectors were fabricated.The measurement results show that the 3 dB bandwidth is 24.1 GHz,which was obtained on a device with a 30 ?m diameter at a wavelength of 1.55 ?m.This value is 39.3%greater than that of a p-i-n photodetector of the same size.Moreover,the responsivity of our device is 0.303 A/W.