Influence of doping level and surface states in tunneling spectroscopy of an In0.53Ga0.47As quantum well grown on p-type doped InP(001)

A steplike density of states is the hallmark of a two-dimensional electron gas. Here, scanning tunneling spectroscopy is used to investigate this property in the differential conductance of an $\mathrm{I}{\mathrm{n}}_{0.53}\mathrm{G}{\mathrm{a}}_{0.47}\mathrm{As}$ quantum well grown on $p$-type doped InP(001). We show that the appearance of a steplike function in the conduction band strongly depends on both the hole concentration in the quantum well and the current injected into the quantized states. Based on four-point probe transport measurements and tunneling-induced light-emission spectroscopy, we discuss the physical mechanisms at the origin of the current and unveil the significant contribution of midgap surface states in the relaxation of the tunneling electrons. These surface states, via pinning of the Fermi level, also affect the potential landscape across the quantum well, as demonstrated by tight-binding calculations of the quantum well electronic structure.