Symmetry of the conduction-band minimum in AlP-GaP quantum wells

Xt–Xlvalley crossover and deformation potential in AlP/GaP quantum wells

“…The conductivity minimum at = 1 appears to result from the lifting of the X t valley degeneracy in high magnetic fields, perhaps due to the exchange interaction; this effect has been reported for Si inversion layers, 13 AlAs/GaAs, 14 Si/ Si 1−x Ge x , 15 and wide AlP-GaP wells. 2 Thus, the single X l valley is lower in energy for AlP QWs with thicknesses of 4 nm and smaller, and the twofold degenerate X t valleys are lower in energy for AlP QWs with thicknesses of 5 nm and greater. Between 4 and 5 nm, the difference in quantum confinement energy between the two types of X valleys must then be equal to the difference in strain energy.…”

“…2,11 The heavy lines in Figs. 2͑b͒ and 3͑b͒ depict the position of the Fermi level as a function of the magnetic field, with a constant electron concentration of n 2d given in Table I.…”

“…Recently, we have established that bulk AlP X valleys are located exactly at the edge of the Brillouin zone, and, in many respects, the valley symmetry in AlP quantum wells ͑QWs͒ with GaP barriers is similar to that in AlAs quantum wells with GaAs barriers. 2 Although AlP and GaP are approximately lattice matched to each other and AlP can be grown pseudomorphically on GaP, a lattice mismatch of about 0.3% causes a biaxial compression in the AlP layers, which lifts the degeneracy at the X conduction band minima by increasing the energy of the longitudinal valleys X l relative to the transverse valleys X t . On the other hand, because the transverse effective mass is smaller than the longitudinal effective mass, m t Ͻ m l , the quantum confinement effect is greater in the X t valleys.…”

“…3 The combined X-valley cyclotron mass in AlP was previously found to be ͱ m t m l = ͑0.52Ϯ 0.01͒m 0 by cyclotron resonance. 2 Further, m l was estimated to have the value m l Ϸ 1.1m 0 based on intersubband absorption in doped multiple quantum wells. 4 To our knowledge, no value for the deformation potential ⌶ u of AlP has been reported.…”

Transport properties of the two-dimensional electron gas in AlP quantum wells at finite temperature including magnetic field and exchange–correlation effects

“…GaP/AlP/GaP quantum well (QW) structures, where the electron gas is located in the AlP, have been studied recently at low temperatures via cyclotron resonance, quantum Hall effect, Shubnikov de Haas oscillations [1] and intersubband spectroscopy [2]. In this structure, due to biaxial strain in the AlP and confinement effects in the quantum well of width L, the electron gas has valley degeneracy g v ¼1 for well width LoL c ¼45 Å, and valley degeneracy g v ¼2 for well width L4L c [3].…”