QW thickness, $d$. Above a critical thickness, $d_c\simeq6.3$ nm H1 lays above E1 so the band structure becomes inverted. In the case of $d\simeq d_c$ linear dispersion relation, i.e., Dirac cone is observed, thus making HgTe QW with critical thickness a single valley Dirac semimetal [@Buettner2011]. HgTe QWs are usually grown in \[001\] direction with iodine or indium doping, however, there are several works devoted to (013) QWs [@Kvon2008; @Kvon2009]. Due to the difference between HgTe and CdTe lattice constants, HgTe QWs are strained. It was found that in wide (013) HgTe QWs with $d\sim20$ nm [@Kvon2011] this strain leads to overlap between H1 and H2 bands with extrema points at different [**k**]{}, thus constituting a 2D electron-hole system.

The most investigated IV-VI semiconductor QWs are PbTe/PbEuTe heterostructures [@Olver1994; @Chitta2005]. They are usually grown on (111) $\text{BaF}_2$ substrate and Bi is used as an [*n*]{}-type dopant [@Rappl1998; @Springholz2013]. Without intentional doping IV-VI semiconductors are typically [*p*]{}-type due to non-stoichiometry; cation vacancies are a natural source of holes [@Parada1969]. PbTe has been chosen as a QW material since it possesses the highest mobility among lead-tin selenides and tellurides [@Khokhlov2002]. In addition, PbTe has a very large dielectric constant ($\epsilon_{\text{PbTe}}=1300-3000$ at helium 