EPITAXIAL METAL(NIAL) SEMICONDUCTOR(III-V) HETEROSTRUCTURES BY MBE

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, En, 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 ΔEn 2. For a nominal well thickness of 3-3.5 nm, ΔEn 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. © 1990.