Interface roughness and period variations in MQW structures determined by X-ray diffraction

Abstract

A method for estimating the interface widths in multiple quantum well (MQW) structures is described. Generally it has been assumed that the average interface shapes on each side of a quantum well are the same, yet there is no reason to assume that this is correct. The method presented here can predict the interface profile on both sides of a quantum well and therefore detect the presence of any asymmetry. The results are compared with the more familiar predictive Fourier transform approach and qualitative agreement is observed, although the latter cannot predict any asymmetry. Deducing the interface width from the predictive Fourier transform method can be difficult because of series termination effects and could possibly be misleading if insufficient satellites are measured. The limitations are essentially by-passed with the described approach. A simple method for deriving period variations is also given and in the example presented this amounts to about two monolayers. The interface widths in this example are 6.5 and 5.4 monolayers and these best-fit values give an R-factor just above that which could be expected from the data. Also the fit for two similarly graded interfaces results in a significant worsening in the agreement.