| Popis: |
This chapter examines some important properties of single and double barrier tunnelling heterostructures. Particular emphasis is placed on the use of magnetic fields in studying not only the tunnelling process itself, but also the way in which electrons relax their energy and momentum. Four topics are examined in detail. First, LO phonon-related oscillations under reverse bias in the I(V) and C(V) curves of single barrier n +GaAs/(A1Ga)As/n −GaAs/n +GaAs and n +(InGa)As/Inp/n −(InGa)As/n +(Inga)As heterostructures are explained by the variation of the impedance of the undepleted section of the n − layers. For the GaAs/(A1Ga)As/GaAs structure, a magneto-impurity resonance at 5 T is observed in the oscillation amplitude, indicating that the impedance variation is due principally to impact ionisation of donors, rather than to LO phonon ionisation. The apparently anomalous behaviour of the magnetocapacitance in these devices in reverse bias is also accounted for. In the reverse-biased (InGa)As/InP/(InGa)As structures, the oscillations in I(V) have period ΔV = 33 meV, indicating that the electron energy relaxation occurs almost exclusively via Ga — As mode LO phonons of the n −(InGa)As layer. |
