Ionized beam doping in molecular-beam epitaxy of GaAs and AlxGa1−xAs

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Abstract
Molecular‐beam epitaxy (MBE) with ion beams as dopants is proposed, and experiments with Zn ions in GaAs and AlxGa1−xAs are reported. In conventional MBE, impurities with low sticking coefficients have not been used because doping into MBE layers involves simultaneous evaporation. In this paper, a method of ionizing the dopant molecular beam and increasing its effective sticking coefficient is proposed. By means of ionization, an effective sticking coefficient of ∼0.03 for Zn ions in GaAs and AlxGa1−xAs is obtained as compared with a value of ∼10−7 for neutral Zn. This value does not vary even with the mole fraction of AlAs in the system AlxGa1−xAs. A strong ion acceleration is not essential for increasing the sticking coefficient, and ionized dopants arriving at the substrate even without enough kinetic energy for penetration beneath the surface react and bond with the surface atoms sufficiently to prevent reevaporation. Crystallographic characteristics of ion‐doped GaAs and AlxGa1−xAs films are as good as for undoped MBE layers and the Hall mobilities are comparable to those of LPE and VPE p‐type layers. Other electrical and optical characteristics are reported here, and the results show that this modification of MBE can be applied to many other dopants and is a useful method to fabricate various electron devices, especially with complicated structures.