Design And Implementation Of A Single-Chip Semi-Insulating Gaas Four-Quadrant Power Laser Positioning Sensor

Laser spot positioning technologies are widely used in the manufacturing fields such as cutting,carving and drilling.At present,four-quadrant-separated positioning sensors based on the photovoltaic effect principle are not only poor in the consistency of the four separated substrate,but also easy to be damaged since that the junctions are not able to withstand higher-power laser irradiation.Therefore,in this dissertation a single-chip GaAs four-quadrant sensor structure is proposed based on the semi-insulating(SI)characteristics and the ultra-fast photoconduction effect of the unintentionally-doped self-compensation GaAs:EL2 material,which structure is especially suitable for the high-power laser precise positioning.Firstly,a four-quadrant sensor with the novel structure is designed,which substrate is a monolithic GaAs:EL2 crystal with a resistivity of 2×10~8Ω·cm.The Ohm-contact electrode of the device top side is made of transparent Indium tin oxide(ITO)and the ITO film is uniformly devided into four blocks by a 50-μm-width crisscross silt.Combined with the semiconductor physical models on the mobility,the recombination,the impact ionization and the lattice heating,the device is modeled.The photocurrent crosstalk between the adjacent quadrants is simulated,and the results show that the high-resistance slit of SI-GaAs:EL2 is able to effectively restrain the quadrant crosstalk which proves the feasibility of the single-chip GaAs device structure.Furthermore,the main parameters affecting the device performances are analyzed,including the laser power density,the slit width,the bias voltage,the carrier lifetime and so on.Secondly,a single-chip SI-GaAs four-quadrant sensor is fabricated through the processes of slit photolithography,,ITO magnetron sputtering and Au ion sputtering.The device dark leakage current is in the order of sub-microampere and the maximum laser power densitie is 146 W/cm~2tested with a 1064-nm-wavelength 100-ns-pulsewidth laser.Finally,the test circuit system is designed.The experimental results show that,the quadrant average crosstalk rate is 2.34%,the responsivity is 33.95 m A/W(@1064nm),and the response consistency is 91%.It means that the design goals is realized since the power laser positioning sensor is of low dark current,low responsivity(to avoid premature saturation),low crosstalk rate,high consistency and high damage light threshold.In addition,a circuit based on the four-quadrant sum-difference algorithm for the GaAs power-laser spot positionging sensor is designed and implemented.