Avalanche multiplication in submicron AlxGa1-xAs/GaAs multilayer structures

A systematic study of the role of band edge discontinuities on ionization r ates in periodic AlxGa1-xAs/GaAs structures has been performed by measuring the electron and hole multiplication characteristics in a series of submic ron AlxGa1-xAs/GaAs multilayer p-i-n and n-i-p structures. These structures comprise alternating 500 Angstrom AlxGa1-xAs and GaAs layers in the intrin sic multiplication regions, with a total thickness of up to 0.5 mu m. The r esults show little dependence on initiating carrier type for multiplication region widths above 0.3 mu m, nor on whether they originate in GaAs or Alx Ga1-xAs. Only alloy-like behavior is observed at all values of multiplicati on up to the breakdown voltage in contrast to earlier work on single hetero junction structures where a large difference was seen at low values of mult iplication between carriers starting in GaAs and AlxGa1-xAs. The microscopi c aspects of hot carrier transport in these devices were studied numericall y using a simple Monte Carlo model. Simulations suggest that the energy gai ned from the conduction band edge discontinuity from AlxGa1-xAs to GaAs is offset by the increased energy loss via the higher phonon scattering rate i n the preceding AlxGa1-xAs layer. We conclude that AlxGa1-xAs/GaAs multilay er structures offer no electron ionization enhancement. (C) 2000 American I nstitute of Physics. [S0021-8979(00)03215-1].