M. Kemerink et al., EFFECT OF STRAIN ON A 2ND-ORDER VAN-HOVE SINGULARITY IN ALXGA1-XAS INYGA1-YAS QUANTUM-WELLS/, Physical review. B, Condensed matter, 54(15), 1996, pp. 10644-10651
We have performed low-temperature photoluminescence and photoluminesce
nce excitation (PLE) measurements on highly degenerate p-type GaAs and
InyGa1-yAs quantum wells. In the PLE spectrum of the GaAs well, evide
nce of a second-order van Hove singularity in the joint density of sta
tes of the ground-state light-hole and electron bands is found. This s
ingularity results from the equality of ground-state light-hole and el
ectron effective masses near the Gamma point, being a much more restri
ctive demand than the usual condition for a van Hove singularity, whic
h requires only the equality of first derivatives of the subband dispe
rsions. The second-order van Hove singularity gives rise to a power-la
w divergence at the singular point, whereas the corresponding usual va
n Hove singularity results in a steplike discontinuity in the joint de
nsity of states. The observed singularity could be described extremely
well by a simple analytical model. The increased energy gap between l
ight- and heavy-hole ground states in the compressively strained InyGa
1-yAs well enhances the valence-band parabolicity, resulting in the di
sappearance of the van Hove singularity. Furthermore, it is shown that
the anisotropic character of the heavy-hole ground state in GaAs is s
trongly suppressed in the InyGa1-yAs system. All experiments are in go
od agreement with our numerical modeling, based on an exact solution o
f the 4 x 4 Luttinger Hamiltonian.