| For high-bit-rate and long-haul fiber optic communications, the avalanchephotodiode (APD) is receiving more and more attention, because its internal gain providesa sensitivity margin. Today,2.5Gbps InP-APDs have been mature for commercial uses,and10Gbps InP-APDs are beginning to occupy the market. However, subject to theunpleasant Gain-Bandwidth-Product (GBP) and noise characteristics of InP material as themultiplication layer, it is difficult to fabricate APDs that can meet the demand s for theapplication of40Gbps and above systems. In this paper, the APD’s GBP and excess noisecharacteristics were studied via circuit model simulation and experimental test respectively,which is inspiring for the design and fabrication of high speed and low noise APDs.Firstly, the APD equivalent circuit model was established. By fitting the experimentdata to get the necessary parameters, and taking the transformation of the carrier rateequations, the APD sub-circuit model for the Cadence PSpice software platform wasderived. This model can be utilized to characterize the DC response, frequency response,and the transient response of the specific InP/InGaAs APD chip. Based on this, the APD’sGBP was simulated, and the influence of the package technique on the GBP wasdiscussed.Then as to study the excess noise characteristic, an improved APD excess noisefactor test system was set up. This new system synchronously measures the gain and noisepower of the APD under test, improving the real-time performance of the measurementand the experimental accuracy. The evident differences on the excess noise factor amongdevices under test were theoretically analyzed, and the effect of non-uniform gain wasexplained. Since the collision ionization is strongly dependent on the temperature, thetemperature dependence of the InP/InGaAs APD device characteristics was investigatedby means of experiment. And finally the temperature dependence of light/dark current,gain, and excess noise factor was interpreted. |
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