Reduction of deep defect concentration in chlorine-doped ZnSe by after-growth thermal treatment

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Abstract
Deep-level transient spectroscopy was applied for investigating the effect of after-growth annealing on the concentration of deep defects in Cl-doped ZnSe epilayers. The samples were grown by molecular beam epitaxy on (100)-GaAs substrates, employing ZnCl2 as the dopant source. The ZnSe:Cl epilayers were annealed in Zn-rich atmosphere at temperatures 400–650 °C for 18–60 h, respectively. As a consequence of the thermal treatment, the total concentration of deep defects in the material was significantly reduced. In particular, annealing almost completely eliminated the dominant defects in the as-grown material (located 0.51 eV below the edge of the conduction band), which strongly supports the identification of the origin of these defects as zinc-vacancy complexes. We also note that the annealing process introduces a small concentration of new defects. The activation energies for electron emission and capture of these traps are 0.24 and 0.17 eV, respectively, indicating that this level lies at 0.07 eV below the conduction band.