The present inventors have found that by exposing a gallium arsenide surface to a downwardly moving ammonia plasma, the gallium arsenide surface can be dry passivated without heating or ion bombardment. Specifically, the sample is placed in an evacuated chamber, the chamber is evacuated, an ammonia plasma is generated at a predetermined distance from a close position of the sample, and the plasma product is moved downward to be in contact with the sample , Stabilizing the exposed gallium arsenide surface of the sample. The gas pressure of the plasma is set to 0.5 to 6 .torr, the temperature of the sample is set to be lower than 100C, and the exposure time is preferably 5 minutes or more. The plasma should be generated at a point sufficiently distant from the sample (about 10C or more) such that ion bombardment on the surface of the sample, which may damage the surface of the sample, does not occur, and that the reactive plasma product may be present in its downward movement range (Within about 30 cm) of the sample. It also places the sample outside the influence of the plasma to avoid damage by radiation (UV, visible and X-ray). As a result, rapid and stable surface stabilization at room temperature, which can be used in conjunction with the batch dry process technique used to fabricate integrated circuits, is made possible.
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