R. Kudrawiec

Contactless electroreflectance of GaInNAsSb/GaAs single quantum wells with indium content of 8%-32%

Interband transitions in GaInNAsSb∕GaAs single quantum wells (SQWs) with nominally identical nitrogen and antimony concentrations (2.5% N and 7% Sb) and varying indium concentrations (from 8% to 32%) have been investigated by contactless electroreflectance (CER). CER features related to optical transitions between the ground and excited states have been clearly observed. Energies of the QW transitions extracted from CER measurements have been matched with those obtained from theoretical calculations performed within the effective mass approximation for various conduction-band offsets (QC) and various electron effective masses. It has been found that the QC increases from 40% to 80% with the rise of the indium content from 8% to 32% and the electron effective mass is close to 0.09m0. The results show that the band gap discontinuity in GaInNAsSb∕GaAs SQWs can be broadly tuned with a change in the indium concentration.

Contactless electroreflectance approach to study the Fermi level position in GaInNAs/GaAs quantum wells

A fruitful approach to study the Fermi level position in GaInNAs/GaAs quantum wells (QWs) has been proposed in this paper. This approach utilizes contactless electroreflectance (CER) spectroscopy and a very simple design of semiconductor structures. The idea of this design is to insert a GaInNAs quantum well (QW) into a region of undoped GaAs layer grown on n-type GaAs substrate. The possible pinning of the Fermi level in the GaInNAs QW region modifies band bending in this system. In CER spectra both QW transitions and GaAs-related Franz-Keldysh oscillations (FKOs) are clearly observed. The analysis of QW transitions allows one to determine the band gap discontinuity at GaInNAs/GaAs interface whereas the analysis of FKOs allows one to determine the built-in electric field in the GaAs cap layer, and, finally, one is able to find the Fermi level pinning in GaInNAs QW region.

On the Fermi level pinning in as-grown GaInNAs(Sb)/GaAs quantum wells with indium content of 8%–32%

Modified van Hoof structures containing GaInNAs(Sb) quantum wells (QWs) with indium content varying from 8% to 32% have been investigated using contactless electroreflectance (CER) spectroscopy. In CER spectra, both the QW transitions and GaAs-related Franz–Keldysh oscillations (FKOs) have been clearly observed. The band gap discontinuity at the GaInNAs(Sb)/GaAs interface has been determined by analyzing the QW transitions. The built-in electric field in the GaAs cap layer has been extracted from the FKO periodicity. The Fermi level position in the GaInNAs(Sb) QW has been determined through knowledge of the electric field in the GaAs cap layer and band gap discontinuity in the GaInNAs(Sb)/GaAs QW. It has been found that the Fermi level is pinned for all samples at the same energy, ∼4.7u2002eV below the vacuum level. The Fermi level is located very close to the Fermi level stabilization energy, ∼4.9u2002eV below the vacuum level. A high concentration of native point defects in the as-grown material is the reason f...

Fermi level shift in GaInNAsSb∕GaAs quantum wells upon annealing studied by contactless electroreflectance

Contactless electroreflectance (CER) spectroscopy has been applied to study band bending in GaInNAsSb∕GaAs quantum well (QW) structures. It has been observed that CER features significantly changes upon annealing: the period of GaAs-related Franz-Keldysh oscillations increases; intensities of excited QW transitions rose compared to the intensity of the fundamental QW transition. The observed changes in CER spectra have been explained by a shift of the Fermi level in the GaInNAsSb layer: the defect states in as-grown GaInNAsSb tend to pin the Fermi level at an energy characteristic for these defects; annealing removes defects from this material and effectively shifts the Fermi level to the conduction band.

Conduction band offset for Ga0.62In0.38NxAs0.991−xSb0.009∕GaNyAs1−y∕GaAs systems with the ground state transition at 1.5–1.65μm

Conduction band offset for Ga 0.62 In 0.38 N x As 0.991�x Sb 0.009 / GaN y As 1�y / GaAs systems with different N contents x = 2.2% - 3.0% and y = 3.1% - 4.3% of N has been investigated by contactless electroreflectance spectroscopy supported by theoretical calculations performed within the effective mass approximation. It has been found that Ga0.62In0.38NxAs0.991�xSb0.009/ GaNyAs1�y quantum wells QWs are promising for laser applications from the point of view of carrier confinement since the conduction band offset QC for these QWs is between 70% and 75%. In addition, it has been shown that GaNAs/ GaAs interface is type I with QC between 80% and 90%.