No abstract

The achievement of high electrical performance InAlAs/InGaAs high-electron-mobility transistors ͑HEMTs͒ grown by metalorganic chemical vapor deposition, requires the growth of a good quality InGaAs channel/InAlAs spacer interface, in order to ensure good transport properties in the two-dimensional electron gas channel. In this article, the interface quality is evaluated as a function of growth interruption time, using photoreflectance spectroscopy. The experimental and theoretical approach used for this purpose is described. Layers representative of HEMT designs, namely 250 Å InGaAs single quantum wells between InAlAs layers were used for characterization. The interface roughness is estimated from the broadening of the high order quantum confined transitions. The results obtained suggest that the higher the growth interruption time, the smaller the interface roughness. Electrical characterization results indicate good agreement with the trends observed by photoreflectance.

Lattice-matched and strained InxGa1−xAs/In0.52Al0.48As single quantum wells with x=0.53 and x=0.60 have been studied by the optical modulation technique of photoreflectance (PR) at room temperature. The measurements have allowed the observation of interband transitions from the heavy- and light-hole valence subbands to the conduction subbands. The PR data have been adjusted with a least-squares fit to the first-derivative functional form. The energetic positions of the optical transitions deduced from the fit have been compared with theoretical values obtained by an envelope function model calculation including strain effects. The best adjustment allowed the determination of the conduction-band offset parameter Qc which is found equal to 0.71±0.07 for the lattice-matched and strained compositions.

We have performed low temperature photoreflectance spectra on several MBE-InAlAs layers lattice matched to InP. Unusual lineshapes of PR spectra are observed at temperatures below 40K, characterized by a step at the InAlAs band gap energy. This step is shown to be related to a strong modification of the photo luminescence background of the photoreflectance spectra. This modification is attributed to an effect of carrier localization due to clustering effects in the InAlAs layers

No abstract