Carrier concentrations, diffusion coefficients and shapes of the Zn profiles in InP layers were compared for various annealing conditions. The Zn-implanted InP:S (4 x 1018/cm3 of active dopant) bulk samples were investigated by implanting them to a fluence of 1016/cm2 at an energy of 150keV and then coating with a 100nm-thick AlN polycrystalline film using sputter deposition followed by annealing (500 to 900C). After removing the AlN films, the extent of diffusion of the implanted species was characterized by using secondary ion mass spectrometry. The depth profiles of in-diffused Zn strongly indicated that the diffusion coefficient was concentration-dependent. The diffusivity of Zn was found to be largest when the InP was annealed using a P over-pressure combined with an AlN cap. In the case of annealing at 700C, a Zn concentration of 2 x 1019/cm3 was achieved. The diffusion range under a P over-pressure was almost twice that in vacuum (figure 10), and this was interpreted in terms of the generation of additional vacancies in the In sub-lattice. The activation efficiency of Zn atoms could be estimated to be about 30%, without additional heat treatment. A Boltzmann–Matano analysis was used to evaluate the concentration-dependent diffusion coefficient of Zn in InP.

Diffusion and Activation of Zn Implanted into InP:S. R.Jakieła, A.Barcz, E.Wegner, A.Zagojski: Vacuum, 2005, 78[2-4], 417-22

Figure 10

Diffusivity of Zn in InP

(Upper plot: under P over-pressure, D (cm2/s) = 9.2 x 10-2 exp[-1.61(eV)/kT]

Lower plot: under vacuum, D (cm2/s) = 1.0 x 10-3 exp[-1.36(eV)/kT])

Figure 11

Diffusivity of Zn in InGaAs/InP

(Zn = 1 x 1018/cm3)