Birefringence induced by the electro-optic effect is demonstrated in vertical-cavity surface-emitting lasers (VCSEL). This is done by comparing two types of optically pumped VCSELs: VCSELs with standard pin-doping and VCSELs with symmetrical pip-doping. The observed birefringence in these VCSELs differs by an order of magnitude, a difference that we ascribe to the presence and absence, respectively, of electro-optic birefringence.

We present the results of optical studies on the energy spectrum of a two-dimensional hole gas (2DHG) in a GaAs/AlxGa1−xAs structure. The photoluminescence (PL) line shape in the 2DHG is investigated as a function of temperature by heating the holes by a current flow through the 2D hole channel. The line shape of the PL from the 2DHG as a function of temperature is calculated by taking into account the real band structure and the hole–hole final-state interaction. By comparing experiment and theory, it is found that the special features of the band structure predicted theoretically explain the experimental data.

No abstract

In situ reflection spectroscopy is demonstrated to be a useful technique for monitoring the damage to the surface of GaAs substrates induced by ions from an electron cyclotron plasma. Distinct differences in the reflectance spectra of GaAs substrates are observed between etching by argon ions and chemical cleaning by hydrogen ions. For argon it is found that the damage layer thickness increases linearly with the argon ion energy. Hydrogen ions induce a damage layer of 3.1 nm and arsenic atoms are preferentially removed from the surface as the ion energy increased.

The composition changes during GaAs oxide removal and the subsequent cleaning with a hydrogen electron cyclotron resonance plasma have been investigated with real-time optical reflection spectroscopy. It is found that the oxide is not completely removed at low temperatures, resulting in a thick damaged surface region. At moderate temperatures (300–500 °C) the plasma exposure is characterized by a two-step process: a removal of the native oxide in a few seconds followed by a gentle etch of the GaAs. In the latter step the plasma exposure leads to a surface region with little damage to the crystal.