COMPOSITION ANALYSIS OF THIN ALXGA1-XAS LAYERS WITH TEM AND SIMS

In this paper two methods for measuring aluminum compositions in very thin (1.5-15 nm), individual ALxGa1-xAs layers are investigated. The transmission electron microscopy (TEM) thickness-fringe method uses the bright-field extinction fringes from a small, cleaved 90° wedge imaged in a [100] orientation. By comparing calculated and experimental extinction fringes, compositions are determined with a sensitivity in x of 0.03, in layers with a thickness of 3.5 nm. With secondary ion mass spectrometry (SIMS), compositions in AhxGa1-xAs layers with a thickness of 15 nm are measured with an accuracy in x between 0.02 and 0.05. Thicker layers (1 μm) with a composition known from x-ray diffraction measurements are used as a reference for both methods. Subsequently, TEM results are compared with SIMS and the reference measurements. The overall agreement is good, but for 0.25 x 0.65, the values of x found by TEM are systematically 0.05 too low. Using the SIMS and reference measurements as a calibration, compositions can be determined by TEM with an accuracy between 0.03 (low x) and 0.05 (high x) in layers as thin as 1.5 nm. © 1990, Materials Research Society. All rights reserved.