Epitaxial metal(NiAl)-semiconductor(III–V) heterostructures by MBE

Abstract

We describe the molecular beam epitaxial growth of NiAl metallic quantum wells as thin as 1 nm buried in III–V semiconductor heterostructures with emphasis on the growth conditions that yield monocrystalline NiAl films with atomically abrupt interfaces. Cross-sectional transmission electron microscope images show that the AlAs/NiAl interfaces contain {100} terraces with ledges of height equal to the NiAl{100} lattice spacing, d, of ∼ 0.29 nm. On the basis of this observation it is argued that the local thickness of an ALAs-clad NiAl quantum well is quantized in units of d. Furthermore, since the de Broglie wavelength of an electron 1–2 eV above the Fermi level in NiAl is nearly commensurate with the lattice at λ = 4d 3 , the calculated subband energy minima, E n, are evenly interleaved such that a composite energy level diagram for a range of well thicknesses displays characteristic energy gaps (for a given in-plane component of the crystal momentum) of ΔE n 2 . For a nominal well thickness of 3–3.5 nm, ΔE n 2 is ∼ consistent with our room-temperature observations of negative-differential-resistance regions in the current-voltage characteristics of AlAs-clad NiAl quantum wells with nominal thicknesses in this range. The large intersubband separation ( ∼ 1 eV) and large electron confinement energies (> 1 eV) of metallic quantum wells offer the possibility of quantum-effect electronic and photonic devices that operate at temperatures and wavelengths that are inaccessible to semiconductor quantum well devices.