The invention is a defect detecting method for a large-size GaAs monocrystalline structure, comprising: grinding and polishing, i.e. mechanically or chemically polishing, where the formula of the adopted polishing solution is that the ratio of sulphuric acid to oxydol to water is 3 : 1 : 1; dislocation corroding, i.e. placing potassium hydroxide in a silver pot and heating to melt potassium hydroxide into a clear state and immediately placing the clear-state potassium hydroxide in a wafer sample for corroding, then taking out the sample and cooling, and then washing with water and blow-dry; selecting measuring direction, measuring point position and number of measuring points, observing visual field area, where the first measuring point is D/10mm apart from the wafer edge and the others are selected at 10 mm intervals, each of which is a measuring visual field; calculating for the selected measuring points. The invention enlarges the range of dislocation density detection, convenient and simple to operate and saving time. |