Thermal Redistribution of Cr in GaAs Due to Damage, Stress and Concentration Gradients

Abstract

The recent availability of a high sensitivity secondary ion mass spectrometer, the CAMECA IMS-3f, has permitted the direct observation of Cr and its movement in GaAs. The high sensitivity (3×10¹⁵ at-cm⁻³) has fostered a variety of studies into the role and redistribution of Cr added to GaAs to render it semi-insulating. The results of these studies provide an insight into phenomena heretofore not understood.

• 1. Cr has been observed to getter into residual damage left after annealing of Se ion implanted SI GaAs (≥lxl0^l4 Se-cm⁻²) [l].

• 2. The near-surface stress caused by thermal expansion mismatch between the annealing encapsulant and the GaAs can getter Cr to the extent that the Cr level is depleted for significant distances into the bulk substrate [1].

• 3. ASBECK, et al., [2], have quantitatively correlated the depletion of Cr with the de-compensation of residual donors, the resultant electrical profile and the performance of a GaAs FET device [2].

• 4. Pre-growth getterinq of Cr into back-surface damage reduces the Cr out-diffusion into as-grown VPE GaAs layers and results in a higher quality epi-layer and materials performance [3].

• 5. The Cr from the substrate outdiffuses into LPE layers on SI GaAs substrates during only moderate thermal processing (850°C for 30 minutes) and can influence the devices grown on that epi-layer [4].

This presentation will provide an unified overview of these data and more recent results on the role and redistribution of Cr in GaAs.