Research Of The High-speed And Wide Spectral Range Photodetector And The GaAs-based Long Wavelength Laser In Optical Fiber Communications

With the rapid development of mobile Internet and big data,the global data business is growing explosively,so is the demand for the network bandwidth.In order to meet such demand,the optical fiber communication system has been pursuing high speed,high capacity and long distance.In the optical fiber communication system,there are two core devices—one is the photodetector,serving as the receiving end of the system;the other is the laser,serving as the transmitting end.It is imperative for the optical fiber communication system to optimize the performance of these two devices.As it is known,there are three kinds of low-loss "window"—the wave bands at 850nm,1310nm and 1550nm.This thesis proposes and then optimizes a novel photodetector with high speed and wide spectral range,which is able to provide high bandwidth and responsivity in the 850 to 1550nm spectral range.Most of the 1550nm lasers used in the optical fiber communication are InP-based InGaAsP lasers.However,the InP-based material is often of high cost,and its Integrated Circuit(IC)technology is not yet well developed.On the contrary,the GaAs material is relatively cheaper and has good electrical properties as well as a more developed IC technology.The development of the optoelectronic integrated circuit(OEIC)can be greatly promoted by adopting the InP/GaAs metamorphic growth pattern which combines good optical properties of InP devices as well as good electrical properties of GaAs metarials.Thus the thesis takes the InP/GaAs integration as the starting point,and then investigates the epitaxial structure and the fabrication and quality test of 1550nm InP laser on GaAs substrates.The main research contents and achievements are listed as follow:1.In this thesis,the basic principles and the performance parameters of the PIN-PD are studied theoretically;the 2D simulation model of the photodetector is built;the relations between the performance of the PIN-PD and the thickness and doping density of each layer are studied in-depth.2.We propose and then optimize a novel photodetector with high speed and wide spectral range in this thesis.An In0.52Al0.48As layer with a wide bandgap is adopted to minimize the surface recombination,since InP-based PDs usually exhibit significant bandwidth and responsivity degradation due to serious surface recombination in the topmost epi-layer.Theoretical and simulation studies indicate that the 3-dB bandwidth of the 20?m~2 active area device is up to 62.5GHz,61.7GHz,and 60.3GHz respectively at 850nm,1310nm,and 1550nm wavelength excitations at 3V reverse bias,and the responsivity is 0.459A/W,0.517A/W and 0.41A/W accordingly.The device is able to provide high bandwidth and responsivity in the 850 to 1550 nm spectral range.3.The thesis investigates the InP/GaAs metamorphic growth.A high quality InP epitaxial layer on GaAs substrates is realized by employing a thin low-temperature(LT)InP buffer layer,thermal cyclic annealing(TCA)and strained-layer superlattice(SLS).The test results show that the dislocation density in this case can be as low as about 1.4×107 cm-2.4.We successfully fabricate the InGaAsP laser on GaAs substrates by working together.We successful fabricate the broad area emitter laser with 50?m P-electrode width and 500?m cavity length.At the room temperature and quasi-continuous wave(QCW)condition,the threshold current is 476mA,and the single slope efficiency is 0.15mW/mA.The output peak wavelength of light is 1549.5nm when the injection current is 700mA.Under the auto-current-control(ACC)mode,the device has been operating for more than 2000 hours at 600mA and room temperature.We successful fabricate the ridge waveguide laser with 30?m stripe width and 500?m cavity length.At the room temperature and QCW condition,the threshold current is 326mA,and the threshold current density is 2.07kA/cm~2.Result of acceleration aging tests shows the device could operate more than 1400 hours.