Investigation of implanted gallium depth distributions in ZnS_xSe_-x by EPMA

Abstract

In the present work EPMA combined with Monte Carlo simulation was applied to investigate implanted gallium depth distributions in ZnS_xSe_1−x layers. The layers of about 1 to 4 μm thickness were grown by MOVPE on (100)-GaAs substrate. The overlap of the Ga and zinc L X-ray spectra and the low gallium net count rates were overcome by stripping the spectra of non implanted layers and by applying appropriate beam currents and counting times. Capabilities and limitations of the EPMA technique as applied to depth profile analysis are demonstrated.

Despite the mentioned L interference, the detectability limit of EPMA for 340 keV Ga in ZnS_xSe_1−x is as low as 10¹⁴ cm⁻². The measured Ga Lα intensity versus beam energy curves reveal variations of the Ga depth profiles during annealing. Evaluation of the intensity curves by means of Monte Carlo simulations yields the implanted dose densities and the first two moments of the depth distributions, i.e. the projected range and its standard deviation. The nonannealed profiles agree well with expectations, but after thermal annealing the profiles were significantly shifted towards the surface. Comparison of EPMA and SIMS results with the example of a non annealed profile in ZnSe has shown good agreement.