Vertical transport in GaAs/ Ga1−yAlyAs barrier structures containing quantum wells: Current–temperature characteristics

Vertical transport in GaAs/ Ga1−yAlyAs barrier structures was investigated using current–temperature (II–TT) measurements in the dark. The samples studied had 500 Å thick Ga1−yAlyAs (0≤y ≤0.26 ) linearly graded barriers between the n+-GaAs contacts and the Ga0.74Al0.26As central barrier containing NwNw (=0, 4, 7 and 10) n-doped GaAs quantum wells of width 35 Å. The thickness of Ga0.74Al0.26As barrier between the wells was 310, 135 and 77 Å for the samples with Nw=4Nw=4, 7 and 10, respectively. The vertical current was measured as a function of temperature (3.5–295 K) at applied voltages in the range 0.01–0.7 V. The total barrier height (ΔUm) and the space charge density in the sample with Nw=0Nw=0, and the effective barrier height (ΔE) for the samples with Nw=4Nw=4, 7 and 10 were determined by analysing the experimental II–TT characteristics using drift–diffusion theory for thermal current. The variation of ΔUm and ΔE with applied voltage was discussed in connection with various dark current mechanisms in barrier structures, including thermionic emission, Fowler–Nordheim tunnelling and sequential resonant tunnelling.