Effects Of Substrate Material Of NDLECSI GaAs On The Performance Of MESFET Devices

GaAs crystal is a kind of III - V compound semiconductor material with excellent electrical performance. GaAs semiconductor devices and integrated circuit are widely used because of their high speed of information processing, super-high frequency, low consumed power, low noise. Metal-semiconductor field effect transistors(MESFETs) with the substrate of nonintentionally doped(ND) semi-insulating (SI) GaAs have been widely used in very large scale integration (VLSI) and monolithic microwave integrated circuit (MMIC). Hence, the study of mechanism for NDLECSI GaAs substrate material to affect the performance of MESFET is very necessary to the design of integrated circuit and fabrication of the devices.. In this thesis, the effects of NDLECSI GaAs substrate material on the performance of MESFET devices have been studied systematically.The deep donor defect EL2 is the dominant donor defect in NDLECSI GaAs, it plays a crucial role in giving rise to the SI property of such materials. In this thesis, a systematical measurement has been made for the distributions of the resistivity, mobility, main deep donor EL2 concentration, shallow acceptor carbon concentration and dislocation density in undoped semi-insulating LEG GaAs crystal by using the methods of Hal! effect, infrared absorption and preferential etching with melt KOH MESFETs were fabricated on the NDLECSI GaAs substrates. The relationship between the substrate parameters and the performance of MESFETs has been investigated, and the correlation between the activation ratio of implanted silicon and the substrate parameters has been also invesitaged.The experimental results are as follows, the distributions for the resistivity, the hall mobility, the EL2 concentration and the dislocation density are inhomogeneous. The distribution of the resitiviry is related to that of EL2 and the distribution of EL2 concentration has a parallel corresponding relationship with that of dislocation density. The distributions of the performance parameters for the MESFETs are also closely related to that of EL2 concentration, the saturated drain current IDSS is larger and the threshold voltage V,,, is more negative for the MESFETs located at the position with high EL2 concentration. EL2 concentration is an important factor affecting the activation ratio of implanted silicon, the activation ratio increases with the increase in EL2 concentration. On the basis of the experimental results, the mechanism for EL2 to affect the Vth of the MESFET is analyzed. It is presented that the effects of EL2 on the activation of the implanted silicon and the Vth of the MESFET originate from theinteraction between EL2 and Si^Si on As site) acceptor, this interation can transforms Si^ acceptor into Si^Si on Ga site) donor.In this paper, the backgating effects of MESFETs on the NDLECSI GaAs substrates provided by different tenders were studied. A backgating threshold voltage|VBST| was found, before the threshold, the drain current IDSS of MESFET was not affected by the |Fgs|, after the |VBS| exceeds the threshold, IDSS would decreasedabruptly with the increase of the |VBS|. The \VBST| of MESFETs on the differentNDLECSI GaAs substrates were different. It is demonstated that the backgating effect are closely related to the electrical properties of NDLECSI GaAs substrate material.