High Performance PIN Photodetectors On Ge-on-Insulator Platform

With the development of the information age,we have higher and higher requirements for the security,transmission capacity,computing capacity,and processing speed of information transmission in the traditional integrated circuit industry.However,Moore’s Law,once followed by silicon-based chips,is declining.The development of silicon-based integrated circuits has encountered many bottlenecks.On the other hand,with the emergence and development of quantum information science,semiconductor quantum computing and quantum chips have gradually demonstrated information processing capabilities and computing capabilities that far exceed those of traditional silicon-based chips.As an excellent candidate carrier system for quantum communication and quantum computing,photonic technology has been developing rapidly in recent years.People expect to realize a monolithic optoelectronic integrated circuit(OEIC)with lower cost,higher performance,and higher integration through silicon-based heterogeneous integration technology.As an important element in OEIC,the photodetector can be used as a light receiver to realize the conversion of light to electricity.The converted electrical signal is further processed in the subsequent circuit to realize the reading and transmission of information.Germanium(Ge)photodetector is one of the key components of the optical communication system.High-speed networks are used in cyberspace security systems,and high-speed and high-response detector modules are required as signal communication modules to ensure stable and efficient transmission of information.Germanium has a high absorption coefficient in the near-infrared and short-wave infrared bands.Its process is compatible with mainstream CMOS processes which is cost-effective.Therefore,Ge is considered to be one of the ideal materials for infrared optical inspection.People have invested a lot of energy in the research of ordinary germanium on silicon(Ge-on-Si)photodetectors and have achieved a series of important results.However,there are still some fundamental problems that have not been resolved.At present,there are few researches on short-wave infrared detectors on Ge-on-insulator(GOI)and related imaging research.This technology is still immature,but this new type of substrate solves the fundamental problem of high defect density of Ge on Si.Its potential application scenarios include semiconductor quantum chips,infrared security systems,safe unlocking of mobile phones,night vision cameras,highend surveillance,and safe driving of unmanned vehicles.This thesis has mainly completed the research and development of new type of high-quality GOI substrate,high-quality GOI PIN photodetectors and its system-level imaging chip working in the short-wave infrared band.The content of the thesis covers basic material research,device-level research,and chip-level research,and has completed a very innovative overall systemic research work.The main research contents and results are as follows:1.Research on the new type of high-quality GOI substrate.A new type of highquality GOI substrate was prepared by bonding method,and the material properties of the GOI substrate were characterized by X-ray diffraction,transmission electron microscope,photoluminescence spectroscopy,and secondary ion mass spectrometry.The characterization results show that the GOI substrate is uniformly doped inside,and there is no inter-diffusion phenomenon in each area,and almost no defects are observed under the transmission electron microscope.The internal tensile strain value of the Ge layer of 0.172%is achieved,and the luminescence peak position of the material has a red shift,which proves that the Ge material quality is greatly improved.2.Research and development of the new type of GOI PIN photodetectors.We introduced the processing flow needed in the preparation of photodetectors on the new GOI substrate.The processes involved mainly include:ion implantation,rapid thermal annealing,I-line lithography,inductively coupled plasma etching,and dry degumming,chemical vapor deposition,chemical solution wet cleaning,physical vapor deposition,chemical mechanical polishing,etc.Three types of detectors were prepared,which are ordinary Ge-on-Si detectors,GOI type-1 detectors,and GOI type-2 detectors.The GOI type-2 detector is a cavity enhanced detector compared to the GOI-1 detector.3.Research on the performance test of the new type of GOI photodetectors.Compared with ordinary Ge photodetectors on Si:In terms of dark current,GOI type1 detector show the lowest dark currents of 2.5nA and 3.8nA at-1V and-2V with a 10μm mesa diameter,which are reduced by 60.9%and 75.6%respectively.In terms of responsivity,the responsivity of the GOI type-2 detector reaches 0.5A/W(quantum efficiency 40%)and 0.9A/W(quantum efficiency 85.2%)at 1550nm and 1310nm wavelengths,which are increased by 56.3%and 66.7%respectively.In terms of highpower characteristics,GOI type-2 detectors have achieved a saturated photocurrent of up to～40mA,which is increased by～135%.In terms of spectral response,the detection range of the GOI detector has been extended to 1630nm.This research has achieved the experimental verification of ultra-high performance GOI PIN photodetector.The GOI type-2 detector with enhanced resonant cavity design has achieved the most excellent optical performance,which provides a good foundation for future single-chip optoelectronic integration.4.Research on N-type Ge contact resistivity.On the heavily doped N-type Ge with a doping concentration of 2×1020 cm-3,using Ni as the contact metal,an ohmic contact with an N-type Ge contact resistivity of 1.3×10-5 Ω·cm2 was achieved.5.Research and development of a new type of shortwave infrared GOI photodetector array imaging chip.Based on the high-performance GOI PIN photodetector,a 128*96-pixel image sensor chip was developed and connected with the PCB imaging readout circuit.Under uncooled conditions,the imaging of the letter"H" and the optical response in the short-wave infrared band have been realized,which proves that the GOI photodetector imaging array chip has the possibility of replacing the imaging chips of similar high-cost Ⅲ-Ⅴ materials.It has laid a solid scientific research foundation for the popularization and application of cost-effective short-wave infrared imaging cameras.