The electrical properties of 60 keV zinc ions implanted into semi-insulating gallium arsenide

Abstract

The electrical properties of chromium-doped semi-insulating gallium arsenide implanted with 60 keV zinc ions have been studied. Hall effect measurements show that the implanted layer is p-type, even in unannealed layers implanted at room temperature. Here the measured Hall mobilities are less than 1 cm²/volt sec. Upon annealing to temperatures as high as 400°C there is a dramatic increase in both the sheet resistivity and Hall mobility for ion doses between 10¹² −3 × 10¹⁴ cm⁻². At higher annealing temperatures up to 800°C the Hall mobility saturates at values near 100 cm²/volt sec for doses in the above range. At the same time the sheet resistivity decreases drastically yielding effective surface concentrations near the total dose. For a dose of 1 × 10¹⁵ cm⁻² the Hall mobility as a function of annealing temperature behaves essentially the same as for the lower doses. However; the sheet resistivity behaves quite differently. Instead of the initial annealing stage, the sheet resistivity monotonically decreases with annealing temperature, and at 800 °C yields effective surface concentrations of less than 10 per cent of the total dose. The differences observed in the annealing of sheet resistivity between the doses of 3 × 10¹⁴ cm⁻² and 1 × 10¹⁵ cm⁻² is taken as evidence that the amorphous threshold lies between these values. Finally, some measurements of sheet resistivity and mobility as a function of measurement temperature suggests that deep-lying defect centers probably dominate the electrical properties of the zinc implanted layers at all annealing temperatures up to 800°C.