Avalanche multiplication in submicron AlxGa1−xAs/GaAs multilayer structures

A systematic study of the role of band edge discontinuities on ionization rates in periodic AlxGa1−xAs/GaAs structures has been performed by measuring the electron and hole multiplication characteristics in a series of submicron AlxGa1−xAs/GaAs multilayer p–i–n and n–i–p structures. These structures comprise alternating 500Å AlxGa1−xAs and GaAs layers in the intrinsic multiplication regions, with a total thickness of up to 0.5 μm. The results show little dependence on initiating carrier type for multiplication region widths above 0.3 μm, nor on whether they originate in GaAs or AlxGa1−xAs. Only alloy-like behavior is observed at all values of multiplication up to the breakdown voltage in contrast to earlier work on single heterojunction structures where a large difference was seen at low values of multiplication between carriers starting in GaAs and AlxGa1−xAs. The microscopic aspects of hot carrier transport in these devices were studied numerically using a simple Monte Carlo model. Simulations suggest that the energy gained from the conduction band edge discontinuity from AlxGa1−xAs to GaAs is offset by the increased energy loss via the higher phonon scattering rate in the preceding AlxGa1−xAs layer. We conclude that AlxGa1−xAs/GaAs multilayer structures offer no electron ionization enhancement.