Study On The Impurity And Microdefects In Semi-Insulating Gallium Arsenide Crystals

GaAs crystal is a kind of III-V group compound semiconductors with good electrical performance. The devices and integrated circuit (IC) fabricated on GaAs substrates have such advantages of hign-speed information processing that they have drawn the researcher's attention. Especially, MESFET devices fabricated on LEC SI-GaAs substrate have been adopted into very large-scale integrated Circuits (VLSI) and monolithic microwave integrated circuits (MMIC) extensively. However, the dislocations, impurities and micro-defects in substrates influence the non-uniformity distribution of electrical and optical characteristic of GaAs material, and the quality and life deeply. Therefore, it is necessary to study the influence of dislocations, impurities and micro-defects in substrates on performance of devices. It is importance to meet the need of design and fabrication of GaAs IC.The dislocations, impurities and micro-defects in LEC SI-GaAs wafers were investigated by means of chemical etching, molten KOH etching, X-ray abnormal transmission, TEM, SEM and Eelectron Probe X-ray Micro-analyzer (EPMA) in this paper. And the influence of these factors on parameters of MESFET was studied.It was found that netlike cell structures or linear structures exist in every SI-GaAs single crystal with high density of dislocation. The nature and formation mechanism of these structures were analyzed for the first time. It is assumed that the cell structures are the clusters of small angle grain boundary caused by the movement and interaction of high density of dislocation, and the cell wall is the typical small angle grain boundary. The phase difference among the small angle grain boundaries increases with the density of dislocation.It was found that the micro-defects in SI-GaAs are the result of agglomeration of point defects. These defects exist as micro-precipitates, small dislocation loops or the complex of impurity and as-grown point defects. The size of micro-defects is in micron rank. The distribution of micro-defects in Φ2" and Φ3" wafers is different. Most of them decorate on...