Enhancement of the 2DEG density in AlGaAs/InGaAs/GaAs P-HEMTs structures grown by MBE on (311)A and (111)A GaAs substrates

The pseudomorphic high electron mobility transistor (P-HEMT) structure materials Al0.33Ga0.7As/In0.1Ga0.9As/GaAs have been grown by molecular beam epitaxy (MBE) on (311)A and (111)A GaAs substrates. The epitaxy of strain heterostructure on high index GaAs substrate has led to new growth phenomena, material properties and device applications. The photoluminescence (PL) spectra of the structures have been measured at low temperature. The dominant emission in the PL spectra is due to the recombination from the first electron (e1) subband to the first heavy-hole (hh1) subband (E11: e1–hh1). This feature (E11) is a relatively broad peak and has a typical asymmetric line shape. The transformation of the PL spectra in the close vicinity of the Fermi edge (EF) under different excitation densities gives strong evidence for the Fermi Edge Singularity (FES) existence. The density of the quasi-two-dimensional electron gas (2DEG) determined by PL study (nsPL), is in sufficient agreement with the values found from Hall measurements nsHall at 77 K. The results prove an increase of the electron density in sample grown on GaAs (111)A and (311)A rather than in equivalent sample grown on (001) GaAs substrate. This effect is in good agreement with our theoretical prediction, which is based on a self-consistent solution of the coupled Schrödinger and Poisson equations.