Determination of surface electric potential by photoreflectance spectroscopy of HEMT heterostructures Article uri icon

abstract

  • We studied a set of AlGaAs/GaAs heterostructures with high-mobility two-dimensional electron gas by room temperature photoreflectance spectroscopy. Electron mobility from 8.8 to 9.6×104cm/Vs was found by Hall effect measurements at 77 K. We carried out PR measurements with two lasers as modulation source: 543 and 325 nm. The spectra showed Franz-Keldysh oscillations (FKO) in two regions: short period FKO from 1.42 to 1.44 eV and broad oscillations in the range from 1.42 to 1.75 eV. The first oscillations are associated to the internal electric field in 2DEG region; the lowest calculated strength corresponded to the sample with the maxima electron mobility. The broad oscillations are unaffected modulation wavelength, which is indicative that they are originated in the surface cap layer. The magnitude of the surface electric field (465-503 kV/cm) from this region was used to calculate the potential profile of the edge of the conduction band by nextnano software. We found a surface electric potential around 0.7 eV, which affects the band structure until to a depth of about 50 nm. On the other side, when the surface is passivated by (NH4)2Sx treatment the broad FKO disappear of PR spectra. © 2013 Elsevier B.V. All rights reserved.

publication date

  • 2013-01-01