| With the fixed broadband entering the era of gigabit optical network and officially incorporated into the outline of the national 14th Five-Year Plan,the vigorous development of emerging applications puts forward higher requirements for the existing communication technology.As the backbone of the global telecommunication network,the optical communication system needs to further carry the exponential growth of data traffic.Photodiode is the core device of the receiving end of optical communication system.The upgrading of high-speed optical communication system is inseparable from the development of high-speed and high saturation output photodiode.Compared with other photodiodes used in optical communication systems,the Uni-traveling Carriers photodiode(UTC-PD)eliminates the impact of low-speed holes on bandwidth and saturation current,and has better high-speed and high saturation performance.In addition to its outstanding performance in high-speed optical communication system,UTC-PD also has great application prospects in wireless communication,spectroscopy and imaging,and has become the research hotspot of highspeed and high saturation output photodiodes.This dissertation focuses on the high-speed and high saturation photodiode in optical communication system,focusing on the high-speed performance and saturated output performance of UTC-PD.The main research contents and innovations of this thesis are as follows:1.The light intensity regulation of UTC-PD bandwidth is studied and a reasonable explanation is given.It is found that for the classic UTC-PD with uniform and highly doped absorption layer,the 3dB bandwidth first increases and then decreases with the increase of incident light power,and there is a 3dB bandwidth peak point;In the process of increasing the incident light intensity,the self induced field formed by the hole drift current in the absorption layer gradually increases,the electron transport speed in the absorption layer gradually increases,and the 3dB bandwidth of UTC-PD increases until the space charge effect reduces the 3dB bandwidth of the device;Increasing the bias voltage can effectively alleviate the space charge and further improve the 3dB bandwidth peak.For the classic UTC-PD with an absorption layer thickness of 220nm and.an active region diameter of 7μm,when the reverse bias is 6V,the 3dB bandwidth of UTC-PD increases from 62.5 GHz@10W/cm~2 increases to 90.1GHz@3.4 × 10~5W/cm~2,the 3dB bandwidth of the device is increased by 44.1%.2.The frequency dependent saturated output characteristics and harmonic distortion of UTC-PD are studied respectively.For the saturated output characteristics of UTC-PD,it is found that the RF output power peak of UTC-PD decreases with the increase of incident signal frequency,and there is a linear relationship between them.For the harmonic distortion of UTC-PD,it is found that when the incident light intensity is large,the larger the signal frequency is,the more serious the output waveform distortion of the device is.In the corresponding spectrum,the signal distortion is represented by the generation of double frequency,triple frequency and higher double frequency components.The effect of increasing the frequency of the incident signal is that the fundamental frequency component decreases and the double and triple frequency components increase.3.A new structure of UTC-PD with high speed and high saturation output is proposed.By introducing radial Gaussian doping into the absorption layer of UTC-PD,Gaussian doping generates a self built electric field in the absorption layer of the device and increases the electron transport speed;At the same time,Gaussian doping introduces a depletion layer into the absorption layer to reduce the device capacitance.Under the combined action of the two,the high-speed characteristics and high saturation output characteristics can be improved.Compared with the classical UTC-PD with the same absorption layer thickness and active region diameter:when the incident light intensity is 2 × 104W/cm~2 and the reverse bias of the device is 2 V,the 3dB bandwidth of the classical UTC-PD is 80.9GHz,and the 3dB bandwidth of the radial Gaussian doped UTC-PD is 118.9GHz,which increases the bandwidth by 46.9%.When the reverse bias voltage is 2V,the RF output power peak of the classic UTCPD is 11.2dBm@50GHz,the peak RF output power of radial Gaussian doped UTC-PD is 13.6dBm@50GHz.The high-speed characteristics and saturated output characteristics of radial Gaussian doped UTC-PD are better than those of classical UTC-PD.4.The influence of the uniformity of radial Gaussian doping in UTCPD absorption layer on the 3dB bandwidth of the device is studied.For Gaussian doped UTC-PD,the uniformity of absorption layer doping is controlled by the characteristic length.It is found that when the characteristic length of Gaussian doping is too large,the doping concentration gradient in the absorption layer is small,which has no obvious effect on the improvement of 3dB bandwidth of the device.When the characteristic length of Gaussian doping is too small,the doping concentration gradient in the absorption layer is large,and the spatial charge effect of the device under high light intensity incidence is stronger,which makes the 3dB bandwidth of the device drop rapidly.Through simulation,it is found that for UTC-PD with diameter of 7μm,when the characteristic length of radial Gaussian doping is between(?)μm～2(?)μm,it can better improve the 3dB bandwidth of UTC-PD.5.The UTC-PD was prepared by post process,and the responsiveness and 3dB bandwidth of the prepared UTC-PD were tested.For the table type UTC-PD with a diameter of 28 μm,the tested response is 0.21A/W;The 3dB bandwidth under 2V,3V and 5V reverse bias is 18.2GHz,20.1 GHz and 21.5GHz respectively,which has good high-speed performance.6、A simulation file generation tool and automatic data processing tool based on Java programming language are realized.The tool can automatically write simulation files and automatically process the simulation output data.It has good stability,ease of use and expansibility. |
PDF Full Text Request