Optical and Electrical Characterization of Pseudomorphic AlGaAs/InGaAs/GaAs Modulation-Doped Structures Processed by Rapid Thermal Annealing

摘要

AlGaAs/InGaAs/GaAs pseudomorphic high-electron mobility transistors (HEMT's) have demonstrated excellent low-noise, high-frequency performance. The advantages of this material system over the lattice matched AlGaAs/GaAs system include larger two-dimensional electron gas (2-DEG) concentrations as a consequence of the lower band gap of InGaAs, and superior transport properties. Good device performance requires epitaxial layers to possess high crystalline quality and abrupt interfaces. To prevent the formation of misfit dislocations in the strained InGaAs channel, it is necessary to keep its thickness below the pseudomorphic limit. We describe molecular-beam epitaxial growth conditions to obtain high-quality pseudomorphic AlGaAs/InGaAs/GaAs modulation-doped structures. We discuss the effects of rapid thermal annealing on the electrical properties of these structures. A mobility increase is typically obtained after short-time heat treatments. We also report the first study of the effects of thermal processing on the optical properties of modulation-doped structures. Both the linewidth and the energy of the photoluminescence transition due to channel electrons and photoexcited holes are influenced by the changing free-carrier concentration in the channel. Our results also suggest that there is negligible layer mixing in these structures after annealing. Reprints. (AW)