Analysis of AlGaAs/GaAs superlattices by means of sputter‐assisted AES, SEM and TEM

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Abstract
This paper reports the developments of evaluation methods on epitaxially grown superlattices by means of sputterassisted Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). AlGaAs/GaAs semiconductor superlattics were grown epitaxially by metal–organic chemical vapour deposition (MOCVD). The layer thickness of the superlattices ranged from a few to ten nanometers.Firstly, developments of Auger depth profiling were tried by using: (1) a differential pumping‐type ion gun instead of a static pressure type to reduce the oxygen adsorbates on the AlGaAs layer; (2) low‐energy Auger signals instead of high‐energy ones to shorten the escape depth; and (3) the lowest ion etching energy of 0.2 keV instead of 1 keV to reduce the surface roughening effects. It is shown that the depth resolution of sputter‐assisted AES is attainable to 1.5 nm.Secondly, high‐resolution SEM can be used as an easy evaluation method by observing the cleaved surface of superlattices, since the layers can be distinguished by signal contrast. Also, TEM can be used as an evaluation method by observing the (110) cross‐section thinned sample. The dark field image has a high contrast between AlGaAs and GaAs using the (002) diffraction.It is confirmed from these AES, SEM and TEM evaluations that the hetero‐interface abruptness of AlGaAs/GaAs superlattices grown by MOCVD is of the order of one monoatomic layer.