Study Of GaAs Threshold Voltage Uniformity And Measurement System

GaAs devices and circuits have many distinct advantages over those of silicon such as high speed, low power dissipation, low noise, wide operation temperature and high radiation hardness. They have been widely used in optical-fiber communication, satellite communication, super high speed computer, high speed measurement instrument, mobile communication, etc. Since GaAs is compound semiconductor, it is difficult to achieve high quality GaAs crystal. The material quality far lags behind the demands of circuits, and restrains the development of GaAs circuits. With the development of integrate circuits and increasing of the integration, the research of the threshold voltage uniformity is becoming more and more important.The GaAs devices , circuits and their development history have been introduced briefly. The models of GaAs MESFET device have been discussed. The drain current-voltage relations have been derived from two region model. The physics model successfully explains its operation principle. But the calculation is complex . Approximations have been made when doing analysis. The influence of process has not been included. These make the model unsuitable for circuit simulation. So many quasi- empirical models such as Curtice model and Statz model are introduced in circuit simulation program such as SPICE.Layout for measuring the uniformity of threshold voltage has been designed, including structures for measuring many material and process parameters. This Layout is adaptable to many process. In order to study the influence of different process on the threshold voltage uniformity, GaAs MESFETs are fabricated both in recessed-gate process and planar selectively implanted process. Results show that threshold voltage uniformity of MESFET fabricated in planar selectively implanted process is better than that of in recessed-gate process.The influence of different process on GaAs MESFET sidegating effect has been studied . These process include Recessed-gate process, planar selectively implanted process and planar boron implanted process. Results show that the sidegating threshold voltage is higher when adjacent devices are isolated by boron implanted, which means that boron implantation significantly improves the electronical isolation between devices and reduces the sidegating effect. We also studied some characteristics of sidagating effect using MESFET fabricated in planar boron implanted process including photosensitive, hysteresis, influence of sidegating effect on MESFET threshold voltage, influence of drain-source voltage on sidegating threshold voltage, influence of exchanging drain and source electrode on sidegating threshold voltage, relation between sidegating threshold voltage and the distance between side-gate and MESFET, relation between sidegating effect and floating gate, and so on. Sidegating effect of different materials is also investigated. Results show that Sidegating effect of VGF growth material is smaller than thatof LEC growth material.A GaAs threshold voltage automatic measurement system is designed. The sample may be 2", 3" wafer. It can save the data, statistic average value and standard deviation of threshold voltage ,map the GaAs threshold voltage. It can also measure the resistivity, backgate effect and so on. This system is the first GaAs threshold voltage auto-measurement system'.of the nation. It will promote the research of the relation between threshold voltage uniformity and GaAs materials. It has great meaning for the improvement of the GaAs material quality of our country.The optical effect on the uniformity of MESFET threshold voltage is studied. Results show that optical radiation enhances the drain-source current of the GaAs MESFET, and makes the threshold voltage to move toward negative direction. Optical radiation enhances the uniformity of MESFET threshold voltage. Deep level defects is one of factors responses for the distribution of MESFET threshold voltage. Optical radiation eliminates the effect of deep level defects on MESFET threshold voltage u...