Me. Daniels et al., HOT-ELECTRON TRANSPORT ACROSS A WIDE ALGAAS BARRIER CONTAINING QUANTUM-WELLS, Semiconductor science and technology, 9(5), 1994, pp. 595-598
An experimental and theoretical study has been made of electron transp
ort over a series of wide AlxGa1-xAs barriers with graded interfaces,
containing GaAs quantum wells in the central Al0.25Ga0.75As region. Ex
tensive measurements of both the voltage and temperature dependence of
the current were made, as well as measurements of magnetoresistance.
In these structures tunnelling is expected to be negligible and hence
drift-diffusion thermionic emission theory was used to interpret the d
ata. Good agreement between theory and experiment was obtained using a
low-field model for electric fields up to 10 kV cm-1. At applied elec
tric fields greater than 10 kV cm- 1 agreement between theory and expe
riment was obtained to within an order of magnitude when the model was
modified to include a saturated drift velocity plus the effect of inj
ected space charge. At high electric fields periodic negative differen
tial resistance (NDR) oscillations were observed. The model usually gi
ven to explain these oscillations involves tunnelling and is, therefor
e, not obviously applicable to these structures. An alternative descri
ption of their origin is discussed, based upon the NDR associated with
intervalley transfer.